FAQ

Microcontroller power source considerations for Arduino

November 17, 2020 By Scott Thornton 1 Comment

Powering an Arduino has a little magic to it. It wasn’t obvious to me when I first started working with them, but Arduinos have on-board regulation. Taking advantage of this allows for longer power supply wiring runs by using a higher voltage power supply than the nominal 5V or 3.3V needed by the microcontroller (MCU) for logic levels. Some Arduinos accept 6Vdc to 16 Vdc of input voltage, which is well above the maximum rating of the MCU, but the Arduino board regulates the supply voltage accurately as well as additional power for Arduino peripherals. I’ve seen veteran engineers baffled as to the reasoning behind powering a 3.3V Arduino with a 9Vdc power supply until it’s been explained to them.

Microcontroller power requirements

Selecting an appropriate power source for microcontroller-based designs is often overlooked. While concentrated effort and forethought may be in the details of the design itself, many performance and reliability problems can be traced back to the selection and connectivity of the power source. The Arduino family of development boards provides solutions for these problems, but it’s easy to get it wrong without a good understanding of what options are available when you’re designing it. It’s not as simple as saying that a 5V Arduino uses a 5Vdc power supply and a 3.3V Arduino uses a 3.3 Vdc power supply.

Arduino power requirements

Many Arduinos use the ATmega328P microcontroller. Microchip’s ATmega328 has a wide range of acceptable Vcc voltages. (Vcc is the regulated DC supply voltage needed to operate an IC and is often referred to as a supply voltage for ICs.) Most commonly, Arduinos are designed to work at either a 3.3 V level logic for low power consumption or 5 V logic to be compatible with legacy TTL logic devices. The examples provided below refer to 3.3 Vdc devices where the power source considerations are more critical. However, the same principles apply to 5 Vdc devices.

Figure 1: Arduino board specifications. (Source: www.arduino.cc)

Example: Arduino Pro Mini

First, let’s assume a circuit design that uses something like the Arduino Pro Mini. The maximum current draw of the Arduino is 200mA. It’s unlikely that the Arduino itself will draw 200mA, but let’s assume that between the Arduino and the other devices connected to it, they draw a total of 200mA. The ATmega328p datasheet shows that the minimum voltage of a logic high at a pin is 90% of Vcc. Thus, if Vcc is 3.3 Vdc, the minimum voltage at a pin that will be considered a logic high is 0.9 * 3.3 Vdc = 2.97 Vdc. Any value seen at a digital pin below 2.97 V is in an indeterminate range and will cause unpredictable results from the Arduino.

There is always some distance between a power source and an Arduino. The greater the distance, the greater the voltage loss across the power supply’s wiring. But how much is lost? Since 26 AWG is a common choice for low power circuit wiring and it’s on the smaller end of the range of wire gauges, there is less copper. Less copper means lower cost. Stranded 26 AWG is a good choice due to the flexibility of routing the wires. The 26 AWG is large enough such that it’s rated for carrying as much a 2.2Amps for chassis wiring, which is more than ten times the 200mA current draw we’ve specified for the Arduino’s maximum current draw for our design. A 3.3 Vdc power supply and 26 AWG seem like a great choice, but let’s take a closer look.

Power source line loss

Quality 26 AWG wire has a resistance of 40.81 ohms per 1000 feet or 40.81 milliohms per foot. With 200mA flowing through the power source’s wires, we’ll have a voltage drop per wire run as investigated below. Keep in mind that we need to run the wire from the power source to the Arduino and then back again the to the negative side of the power source. We can see that at ten feet, we’ve lost 5 percent of our 3.3 Vdc source. At 20 feet, we’ve lost almost 10 percent. This action reduces the voltage applied to the Arduino to just 4.5V; the low limit of our guaranteed maximum digital logic high voltage.

Table 1: Line Loss. Distance indicates the physical distance between the board and its power supply. (Source: Author)

Twenty feet seems like a reasonable distance for most applications. However, we’ve only considered the resistance of the wire itself to this point.

Contact resistance

Contact resistance is often not considered or even understood. The resistance of the 26 AWG wire is 40.81 ohms per 1000 foot based on the cross-section diameter of the wire. However, every point in the wiring where we’ve placed a connection in the wiring, we have created a point where the cross section of the current path decreases, and therefore have a higher resistance point.

Mating a circular connector will only make the pin contact the barrel at a tangential point. Blade connectors produce the same reduced area across the surface. Even a screw terminal can’t match the cross-section resistance of the wire itself. Consider that any termination is susceptible to oxidation over time and increased resistance by connecting and disconnecting the wires multiple times over the life of the system. Each of these points can easily have a contact resistance of 40 milliohms. That’s right; each connection point can add the equivalent resistance of 1 foot of 26 AWG wire. With two connections landed on the Arduino and two connections at the power source, any system will have a minimum of 4 terminations. We now have a voltage source loss of 5 percent at 8 feet and 10 percent at 18 feet between the Arduino and its power source.

Table 2: Line Loss and Contact Resistance

Single supply choice – varied distances?

Therefore, with a typical power source wiring setup, we’re losing five percent of the 3.3V source voltage between the power supply and Arduino at eight feet and 10 percent at 18 feet. In simple terms, if we were using an adjustable dc power source, we could increase the voltage to compensate for the line loss and contact resistance. However, power supplies are expensive and take up space. Typically, in embedded systems, designers try to have a common power source for multiple embedded controllers. If one controller is one foot away from the supply and the last one is 20 feet away from the power source, the designer has a delicate balancing act to keep each embedded controller within the proper range.

Arduino power source options

Arduino designs give you a way to work around the line loss and contact resistance power source problems by providing on-board regulation. However, there are several ways to power the Arduino and not all of them provide the benefit of on-board regulation:

USB Power – A USB cable is commonly used to program an Arduino through the Arduino Integrated Development Environment (IDE). Not only does the USB cable provide diagnostics through the IDE serial monitor, but it also offers 5Vdc power to the Arduino through the USB Vcc pin. The 5V USB power is used to power a 5V Arduino directly, or it’s regulated down if it’s a 3.3Volt Arduino.

5V or 3.3V Power – The designer can apply the appropriate voltage to the 5V or 3.3V power pins of the Arduino. These pins are tied directly to the power pins of the MCU on the Arduino board. However, applying power to these pins will cause the MCU of the Arduino to be susceptible to the line loss and contact resistance loss from the power source mentioned earlier.

Vin or Raw – Arduino may have this pin labeled either “Vin” or “RAW” depending on the Arduino Variant being used. A common mistake is to apply a 5V or 3.3V power source to this pin. The problem with this is that not only do you have the line loss and contact resistance loss mentioned earlier but that this pin is the input to the on-board regulation circuit. Like any voltage regulator, you need to supply slightly more voltage into the device than you expect to get out of it. If we applied 3.3 Vdc to Vin, we would lose about 0.5 volts through the regulator. That means the microprocessor and connected peripheral devices would only be running on 2.8 Vdc, at best. Combined with our noted line loss and contact resistance loss, we can be running well below our required voltage level.

Table 3: Line Loss, Contact Resistance, and Regulator Loss

V_IN pin, properly used

Despite the problem described above, using the V_INor RAW pins are the solution to the source voltage loss. On the Arduino board, the V_INor RAW pins are the input to the voltage regulator on the Arduino board. All we need to do is apply a voltage in the specified range to get the desired regulated output to the Arduino. A supply voltage of 6 Vdc to 12 Vdc applied to Vin, or RAW will power the Arduino’s microcontroller, overcome any line or contact resistance voltage loss, and provide power output to the 5V and 3.3V pins of the Arduino to power peripheral components. The range of the Arduino’s input voltage is based on the voltage requirements on the entire board, including the energy required for the MCU to powering peripherals.

Conclusion

Off-the-shelf power supplies within the range of 7 Vdc to 12 Vdc are not as common as 3.3Vdc or 5Vdc power supplies, but they are available. It’s tempting to use the more common 5 Vdc and 3.3 Vdc power supplies for Arduino boards, but from the facts presented above, it’s necessary to use the less common alternatives for the best regulation and microcontroller performance.

The Iridium global satcom system, Part 5: Advances and competition

November 6, 2020 By Bill Schweber Leave a Comment

This worldwide satellite-based communications system went from dream to reality in a decade but quickly failed in the market; its revival took persistence and luck, plus a new customer base.

Of course, there were also significant technological advances required in many areas, including designing and building longer-life electronics despite the unavoidable effects of space radiation on electronics. While the life of these electronic components in this environment is a function of the specific component and technology as well as orbit height (or space path), a typical figure can be as little as a few years or up to about ten years.

One way to deal with the effect of radiation is to use radiation-hardened (rad-hard) devices. Component vendors have developed various sophisticated process techniques to provide this performance. However, such devices are generally too expensive for the commercial world in which these global systems compete, and the availability of these devices in quantity was uneven. Also, many of the desired and needed latest generation ICs were unavailable as rad-hard components, or the qualification period for these special devices is too long for them to be competitive.

(Note that the situation is changing due to the widespread use of LEO satellites, SpaceCube satellites, military links, and more, resulting in more vendors are offering space-qualified, rad-hard qualified components, but that was not the case for Iridium’s designers.)

Designers of the Iridium satellites used a combination of techniques to overcome these problems.

Using commercial ICs that have a few extra process steps added, which adds some rad-hard characteristics at a relatively low incremental cost.
Using circuit design with extra guardbands and tolerancing to allow for parametric drift.
Adding redundancy, error detection and correction, and resets to accommodate hard and soft failures.
Selectively using tungsten/copper radiation shielding reduces the electron (but not the proton) aspect of radiation but adds a weight penalty.
Acknowledging that radiation will limit a satellite’s operating lifetime and, therefore, putting standby spares in orbit and planning to launch new satellites regularly.

The original clusters of Iridium satellites performed remarkably well (three times past its original life expectancy), and all were finally replaced in January 2019 with a next-generation fleet – a real testament to their design integrity. Called the “Next Fleet” satellites, each weighs1875 pounds/850 kg, and France-based Thales Alenia Space built all in an Arizona facility (Figure 1) (Motorola built the original Iridium satellites, also in Arizona).

Figure 1: The replacement of the Iridium satellite constellation was completed by January 2019 with new “Next Fleet” satellites made by Thales Alenia Space; the existing satellites were “decommissioned” by directing them to de-orbit and burn up. (Image: Thales Group)

There is some irony or justice here: SpaceX launched these Iridium replacements, and it was Iridium’s concept and efforts which paved the way for adopting mass production and launching of large clusters of SpaceX/StarLink LEO satellites – which may even soon compete with Iridium, and SpaceX did not even exist during the Iridium project’s initial deployment.

Not the only player now

The Iridium system is not the only one which provides some degree of worldwide satellite-based communication for voice and data. Competitors include Globalstar Inmarsat and Thuraya (plus the possibility of a SpaceX/Starlink system):

Globalstar was created from a section of Ford Aerospace in 1991 and works closely with Qualcomm for components and technology. The system uses an LEO satellite constellation consisting of 48 active satellites, placed in orbit about 900 miles in space. Unlike Iridium, which uses the satellites as orbiting MTSOs, Globalstar uses a less complex technique called bent-pipe. Still, a satellite always needs to have both the handset and the base station in sight. Thus, there is no coverage over the Earth’s poles as the satellites do not illuminate those areas.

Thuraya is a large-footprint regional network based in the United Arab Emirates which uses two Boeing-built geosynchronous satellites to provide mobile coverage to more than 110 countries in Europe, the Middle East, North, Central, and East Africa, Asia, and Australia, but not the Western Hemisphere or the poles (Figure 2). However, the phones also incorporate standard cell-phone technology, so conventional cell coverage is worldwide as long as there is a cell system in range. The longer satellite path link means a weaker signal and thus less-consistent service, while the geosynchronous orbit incurs a much longer path-length propagation delay, which can be a problem.

Figure 2: The Thuraya satellite network uses two geosynchronous satellites to provide coverage of roughly one hemisphere and neither pole. (Image: Thuraya)

Inmarsat originated from the International Maritime Satellite Organization (INMARSAT), at the request of the International Maritime Organization (IMO) – the United Nation’s maritime body – but is now a private UK-based company. It uses thirteen geostationary telecommunications satellites which operate in subgroups to provide three levels of footprint and performance: global beam coverage from latitudes of −82⁰ to +82⁰; regional spot beam coverage which operates with significantly smaller antennas; and narrow spot beam coverage (about several hundred kilometers in diameter) via three of its satellites and which can use even smaller antenna while supporting much higher data rates.

Conclusion

Looking back at satellites’ earliest use for communication, they were envisioned only as relay points in space between large, land-based dish antennas. Low-earth orbit satellites provided only sporadic coverage and used small but fast-tracking dish antennas to follow the LEO satellite. In contrast, geostationary satellites provided a constant link and were supported by much larger but relatively fixed dish antennas. In just a few decades, the technology has advanced to where true worldwide coverage is available for voice and data using a convenient handset and no dish antenna. No single technology advance made this possible, but the Iridium system showed what could be done when personal energy, radical innovation, commitment, personal connections, money were focused on making technical “dreams” into reality.

EE World Content

Iridium Satellite Connectivity Added to Versatile ConnectPort X5 R Rugged Gateway
DeLorme Unveils Plans for Iridium-Based Two-Way Satellite Communicator
Basics of GPS receivers
GPS, Part 2: Implementation
GPS, Part 1: Basic principles

External References

“Eccentric Orbits: The Iridium Story,” John Bloom, Atlantic Monthly Press, 2016.
“Iridium Will Host Science Payloads,” IEEE Spectrum, Nov. 30, 2009
“The Collision of Iridium 33 and Cosmos 2251,”Aerospace, December 10, 2015
“A guide to useful, useless, official and unofficial Iridium websites”
“The Rise and Fall and Rise of Iridium,” Air & Space Magazine, September 2004
“Iridium ends legacy satellite service, switches all traffic to Next fleet,” Space News, February 2019
“SpaceX completes Iridium Next constellation,” Space News, January 11, 2019
“Iridium starting to deorbit legacy satellites as Next constellation comes online,” Space News, May 1, 2017
“Elon Musk’s Ambitious Communication Project to Ring Earth with 40,000 Satellites,” News18, Sept 19, 2020
Wikipedia, “Starlink”
“Starlink: SpaceX’s satellite internet project,” com, January 17, 2020
Thales Group, “Happy Birthday Iridium Next,” January 14, 2020
PhoneIsMobile, “Iridium Satellite Phone”
Wikipedia, “Iridium satellite constellation”
Wikipedia, “Inmarsat”
Wikipedia, “Thuraya”
Wikipedia, “Globalstar

8-bits and counting: 8-bit MCUs are still going strong

November 6, 2020 By Scott Thornton Leave a Comment

Microcontroller units (MCUs) never stop evolving; a more functional, featured MCU follows every model. Embedded systems have grown with continually growing MCU technology, yet there are many traditional MCUs that are still selling in high volumes. Atmel 8051 is one of those legendary MCUs which have developed a considerable demand in the market.

The Atmel 8051 is one of the bestselling descendants of the 8-bit Intel MCS-51. Four decades ago, Intel introduced an 8-bit MCU with limited features, the MCS-51. In just a few years after launch, the 8051 design was leading the embedded market and multiple manufacturers introduced their own versions of the 8051. For several years the 8051 MCUs offered appealing functions and features that increased growth for this architecture as more designs piled up for a multitude of end products.

Back in the 1980s, there were very few MCUs with comparable features to the 8051 architecture as the best option for embedded products. Decades later, what’s keeping the 8051 alive?

8-bit MCUs — Figure 1: Intel® P8051 microcontroller. (Source: en.wikipedia.org)

Today’s 8051 MCU applications

Continual improvements to 8-bit MCU architectures help them retain MCU unit sales volumes, even with cost-competitive 32-bit MCUs. Today’s 8-bit MCUs are still landing new and legacy design-in sockets that require lower prices, ultra-low power consumption, and small physical form factors. For example, an 8-bit (one byte) wide processor consumes less power than 16- or 32-bit MCUs. The latest Cortex M7 based 32-bit MCUs can process at speeds of hundreds of MHz, yet the use of traditional 8-bit MCUs are not declining in the market.

Many commercial product vendors still trust the 8051 MCU for various reasons, the most prominent being low cost and low power consumption. Despite the more limited features and old architecture, the 8051 is still used in some wireless communication products. The latest HC-10 Bluetooth modules are based on 8051 core. Although 16-bit or 32-bit MCUs can replace the functions offered by 8051s, the 8-bit MCU is sufficient for many product developers. Another reason for retaining 8-bit MCUs is that 8-bit MCUs are easier to program and troubleshoot than 16- and 32-bit MCUs because there’s physically fewer bits to address, debug, and investigate.

Examples of 8051 MCU-based devices include Bluetooth gadgets,[i] wireless transceivers, used inside the communication system of wireless power meters, and more. [ii] No doubt the modern transceivers based on 32-bit cores are exceedingly effective, but 8051 MCUs are suitable for low-cost products, especially for products where one cent in savings per unit makes a huge difference at high volumes.[iii]

Apart from commercial products, 8051 MCUs are still actively used in academic activities, as well. Many academic institutions still prefer the architecture and programming of the 8051 for teaching basic embedded systems and relevant topics. For example, it’s much easier to wrap your brain around 8-bit constructs than 16- or 32-bits in terms of detailed study of operations, memory, addressing, and so forth. Project development boards are widely used in coaching activities, which is why 8051-based development kits are still in demand today.

Aside from 8051 MCUs, many other 8-bit MCUs have made their way into commercial products. Microchip is undeniably the largest supplier of 8-bit MCUs. Microchip’s low-cost 8-bit chips are accompanied by free tools, which also buoys 8-bit MCUs as a low-cost option. An 8-bit MCU can accomplish more than would be expected. For example, in 2014 OPU SAT was launched into space with a Microchip’s 8-bit PIC16F877 MCU controlling its communication system.

8-bit MCUs used in satellites

Figure 2: System block diagram of OPU Sat. (Source: directory.eoportal.org)

Even though 8-bit MCUs have made their way into space, wider-bit MCUs are preferable for areas demanding a higher level of processing. The OPU SAT also contained a Microchip 16-bit PIC24FJ256GA110 MCU in its command and data handling unit.

The PIC24FJ256GA110 MCU is somewhat famous in satellites as it has been used in other satellites as well. The PIC24FJ256GA110 MCU was also used in the Aeneas 3u Satellite as a flight processor. [iv]

8-bit MCUs can clock at decently high frequencies considering that many applications don’t require massive amounts of rapid calculations. Some applications only need to check a status once a minute, for instance. Thus, 8-bit MCUs are more than enough for many applications. The central processing unit, in many cases, is a minuscule part of most devices with multiple peripherals. The Atmel 8051 MCU has certain limitations for its peripherals as compared to 32-bit MCUs. However, there are many applications for MCUs where the peripherals are enough for developing products that do not involve intense, high-speed processing.

Several general-purpose input/output (GPIO) lines, Pulse Width Modulation (PWM), and some flash memory can be suitable for small-scale projects. However, as a significant drawback, the 8051 MCU does not support Analog to Digital Conversion (ADC), and an external ADC has to be connected to it for reading analog signals. Nevertheless, there are many 8-bit MCUs with an integrated ADC, such as Microchip’s ATtiny202/402 AVR MCUs. However, 32-bit MCUs with ADCs typically have multiple ADC channels on the chip. Some 8-bit MCUs have Digital to Analog Converters (DACs) on-chip. Nevertheless, the cost-cut with 8051 MCU as compared to 32-bit MCUs enables low-cost production.

Memory is also an area of difference between 8-bit and higher-bit MCUs. For instance, 64 KB of flash memory in an 8051 MCU is insufficient for detailed instructions whereas 32-bit MCUs like the ATSAMS70Q20B MCU have 2 MB of flash memory. Not every MCU project requires flash memory as high as 2 MB.

In the end, it’s true that most 8-bit MCUs are no match to 32-bit MCUs in terms of speed, processing capability, support for numerous peripherals, and memory, but 8-bit MCUs are still more suitable for devices where extensive features and high processing speed are not essential.

Communication protocols

Traditional MCUs have limited communication protocols, but over time, MCUs have evolved. Multiple communication protocols are necessary for extensive circuits where an MCU has to communicate with other devices. For example, the Microchip ATSAMS70Q20B MCU supports Master Controller Area Network (MCAN), Serial Peripheral Interface (SPI), I²C (Inter-Integrated Circuit), Ethernet, Universal Serial Bus (USB) and the Universal Asynchronous Receiver-transmitter (UART). However, the 8051 MCU supports limited communication protocols which restrains its use in areas where multiple communication protocols are required. Thus, for limited communication protocols, 8051 MCU can serve the purpose.

Power consumption

When choosing an MCU, special attention is most often paid towards the power budget and requirements. MCUs consume considerable power during operation, so several levels of idle and sleep states can make a difference during inactivity. The latest MCUs can sleep during inactivity which saves considerable power in the long term. Traditional 8-bit MCUs such as 8051 may not have any such features. Sleep states during inactivity can make a large impact on power consumption, so older MCUs consume more power than modern MCUs with otherwise equivalent features.

8-bit MCUs still going strong at Microchip

Microchip is still producing new 8-bit MCUs, generating a significant amount of revenue from 8-bit MCUs. Silicon Labs also releases new 8-bit MCUs. 8-bit MCUs are still used in plenty of products in legacy products and in new designs. 8-bit MCUs tend to be easier to program and understand on a deep level compared to 32-bit MCUs and are not likely to go away as long as an 8-bit MCU costs less than an equivalent 32-bit MCU.

[i] https://www.alibaba.com/product-detail/High-performance-and-low-power-MCU_60391542233.html?spm=a2700.7724838.2017115.93.106b4e3dyptiH4

[ii] http://www.ti.com/product/CC2511

[iii] https://www.alibaba.com/product-detail/Good-Quality-Integrated-Power-meter-with_60770229988.html?spm=a2700.galleryofferlist.normalList.129.60741e813LizGS

[iv] https://earth.esa.int/web/eoportal/satellite-missions/a/aeneas

The Iridium global satcom system, Part 4: Lessons learned

November 6, 2020 By Bill Schweber Leave a Comment

This worldwide satellite-based communications system went from dream to reality in a decade but quickly failed in the market; its revival took persistence and luck, plus a new customer base.

Today, Iridium is a viable mobile, satellite-based, which handles voice and data. As with standard cellular systems, its users have little or no idea of what it took in innovation, radical thinking, technology, money, undaunted determination, more money, and mistakes to make it possible. In case you are wondering what Iridium access costs, the phones (which now also include standard cellular-access capabilities and SIM cards) run about $1000 while the service has many pricing factors depending on speed, usage, voice/data mix, and use of prepaid minutes and cards; the “PhoneIsMobile” reference at the end gives some examples of pricing.

Lessons learned

The technical success, business failure, and rebirth of Iridium provide multiple lessons for advanced-technology projects. Among them:

Technically audacious ideas and dreams can drive astounding engineering feats—with enough funding.
A relentless champion is needed to drive the mission from the start and revive it after setbacks if needed.
It’s easy to believe your own market projections of the size of potential customer base and skip any reality checks.
Satellite production, launch, and management can be transformed into a quasi-mass-production process, in contrast to the one-off, fully customized satellite designs and associated operation that was the norm at the time and was for many years. Now, however, we have tens of identical low-Earth orbit (LEO) satellites launched on a single rocket in a mass-production/deployment operation.
Rocket launches can also be successfully done on a “high-volume” basis using multiple contract launch services. Each early Iridium launch-cycle “kit” included the multiple satellites plus fuel for their steering thrusters, battery sets, the set-up and test instrumentation, an office, and everything else needed except the launch rocket itself. Total kit weight per launch was about 500,000 pounds, with shipping arranged through FedEx in many cases!
Regulatory issues such as spectrum allocation and approval can be time-consuming in just one country and become exponentially worse when multiple countries or jurisdictions are involved.
Local political connections and personal contacts with key influencers in each country’s bureaucracy are essential, and some quasi-ethical steps are often part of the scenario.
Small, unplanned items can have unintended consequences, for both good and bad. For Iridium, the originally non-existent concerns about unburned debris liability became a major sticking point. They stalled the final order for the satellites’ physical demise long enough to allow a rescue plan to come together.

The final part of this article looks at one area of advances and the competitive landscape today.

EE World Content

External References

“Eccentric Orbits: The Iridium Story,” John Bloom, Atlantic Monthly Press, 2016.
“Iridium Will Host Science Payloads,” IEEE Spectrum, Nov. 30, 2009
“The Collision of Iridium 33 and Cosmos 2251,”Aerospace, December 10, 2015
“A guide to useful, useless, official and unofficial Iridium websites”
“The Rise and Fall and Rise of Iridium,” Air & Space Magazine, September 2004
“Iridium ends legacy satellite service, switches all traffic to Next fleet,” Space News, February 2019
“SpaceX completes Iridium Next constellation,” Space News, January 11, 2019
“Iridium starting to deorbit legacy satellites as Next constellation comes online,” Space News, May 1, 2017
“Elon Musk’s Ambitious Communication Project to Ring Earth with 40,000 Satellites,” News18, Sept 19, 2020

The Iridium global satcom system, Part 3: Very nearly crash and burn

November 5, 2020 By Bill Schweber Leave a Comment

This worldwide satellite-based communications system went from dream to reality in a decade but quickly failed in the market; its revival took persistence and luck, plus a new customer base.

Iridium’s launch, crash, and nearly burn (literally)

The Iridium communications service was initiated on November 1, 1998, with a call by then-Vice President Al Gore. After several months of working through technical issues, the system actually worked fairly well and met most objectives. Potential users were impressed, and the initially skeptical technology community was impressed that Iridium went from an idea to a fully operational system in a little over a decade.

On the business side, though, things were dismal. Instead of tens of thousands of users willing to pay thousands of dollars for a phone and about $10/minute for a call, the system only signed up a few hundred. Among the reasons is that the anticipated market of world-wide business travelers never materialized, due to the cost and size of the handsets and calls, the fact that most such travelers were in areas that had cellular service, and an Iridium technical weakness that the caller had to be outside to “see” the satellite. In contrast, conventional cell calls could be done from inside most buildings.

Iridium Satellite LLC (the official name) went into Chapter 11 bankruptcy in less than a year. What took a little over a decade to create and implement took just nine months to crash figuratively, and it seemed the literal crash come soon thereafter. Motorola would not tolerate the $200 million/month ongoing operating costs with no prospect of eventual turnaround; simultaneously, the gateway owners demanded make-good on their expected revenue, and the system needed planning for additional satellite launches as spares.

Motorola said the solution to this never-ending financial drain was easy and clear: write off the loss, and kill the system and shut it down, which included de-orbiting the satellites by directing them into lower orbits where they would soon begin reentry and burn up. The picture was both bleak and apparently hopeless.

Over the next few months, Motorola issued several “firm and final deadlines” saying if the system did not find a buyer by a specified, very close date, the satellites would be instructed to de-orbit with 48 hours of that deadline; each time, the deadline was put off due to pleading from a small group of tireless Iridium proponents who sought new investment partners in the $20 to $100 million range around the world, including poor African countries who wanted both the connectivity access and prestige and their portion of the ongoing gateway revenue.

Back from the near-dead

A break came for the unlikeliest of places when a New York Times article on the Iridium situation mentioned that some of the satellites might not burn up completely, and some debris might land on inhabited areas or even hit someone. Suddenly, legal liability became the dominant issue preventing issuing the de-orbit command, with concerns about who would have that liability, who would insure against it, and how that would happen. This potential debris issue – and it was a real but actually quite a minor possibility based on previous satellite burn-ups – became the delaying element which kept Motorola from issuing the formal de-orbit order and bought time for more tries at survival.

Eventually, after countless issued and withdrawn deadlines and hunts for funding, the remaining Iridium team, led by Dan Colussy, a retired CEO of Pan, heard about Motorola’s plans and decided he would buy Iridium. After considerable effort, he was able to pull together financing from private investors and the US Department of Defense (DoD), who became convinced after many meetings and PowerPoint presentations that Iridium was a valuable and irreplaceable resource for the military. Critical to this decision was the reality that the Colussy’s Iridium team – mostly aerospace industry veterans and former DoD insiders – knew the right people to talk to, or at least knew people who could help them get meetings with the key influencers and decision-makers at the Pentagon.

The DoD funding came from a “special fund,” used for special projects and did not require any formal tender or bidding but is instead reserved for projects deemed critical for national security. Potential Iridium competitors such as Globalstar protested, but these were denied under “critical to national security” rules. (Note that Globalstar’s proposed system was technically far less advanced, as it used the satellites only as relay points from earth-satellite-earth connections. This is known in the industry as a “bent pipe” arrangement and may require several “hops” between callers; in contrast, the Iridium system used the satellites as a sophisticated meshed network with far less propagation delay since call routing was done dynamically by the mesh itself.)

The assets of the bankrupt company, Iridium Satellite LLC, were purchased for $35 million (compared to a cost of billions) by the newly created owner, Iridium Communications, Inc., a publicly-traded (NASDAQ) company. All the gateways have been shut down except for a commercial one based in Tempe, Arizona, and a DoD one in Hawaii.

But the story does not end there. Like a fairy tale or the legendary Phoenix bird of many cultures (known for its ability to live for many years before dying in a burst of flames, only to be reborn from the ashes), Iridium was reconstructed, rebuilt, and restarted. As of 2019 company has 782,000 subscribers, with 72,000 of them government subscribers. They have expanded from basic voice service to broadband service for higher-speed data. They are actively working on a full set of 3rd-generation satellites for even higher-speed performance and capacity, at the cost of just under $2 billion. Among the commercial users are oil rigs, ships, desert mining sites, and even Antarctica’s year-round scientific bases.

The next part of this article looks at some of the “big picture” lessons and context of the Iridium project.

EE World Content

External References

“Eccentric Orbits: The Iridium Story,” John Bloom, Atlantic Monthly Press, 2016.
“Iridium Will Host Science Payloads,” IEEE Spectrum, Nov. 30, 2009
“The Collision of Iridium 33 and Cosmos 2251,”Aerospace, December 10, 2015
“A guide to useful, useless, official and unofficial Iridium websites”
“The Rise and Fall and Rise of Iridium,” Air & Space Magazine, September 2004
“Iridium ends legacy satellite service, switches all traffic to Next fleet,” Space News, February 2019
“SpaceX completes Iridium Next constellation,” Space News, January 11, 2019
“Iridium starting to deorbit legacy satellites as Next constellation comes online,” Space News, May 1, 2017
“Elon Musk’s Ambitious Communication Project to Ring Earth with 40,000 Satellites,” News18, Sept 19, 2020
Wikipedia, “Starlink”
“Starlink: SpaceX’s satellite internet project,” com, January 17, 2020
Thales Group, “Happy Birthday Iridium Next,” January 14, 2020
PhoneIsMobile, “Iridium Satellite Phone”
Wikipedia, “Iridium satellite constellation”
Wikipedia, “Inmarsat”
Wikipedia, “Thuraya”
Wikipedia, “Globalstar”

The Iridium global satcom system, Part 2: The implementation

November 4, 2020 By Bill Schweber Leave a Comment

This worldwide satellite-based communications system went from dream to reality in a decade but quickly failed in the market; its revival took persistence and luck, plus a new customer base.

The first part of the article explained the inspiration and rationale for the Iridium system. Three major elements were required to make the Iridium concept and dream – and it was truly a dream – into reality:

Figure 1: The six polar orbits of the Iridium system show how its orbital planes provide complete coverage of the Earth’s surface. (Image: University of Colorado/Colorado Center for Astrodynamics Research)

1) A global constellation of 66 satellites (plus about half a dozen or more “spares”), but not in the usual geosynchronous orbits or even low-altitude, low- propagation-delay orbits. Instead, polar orbits would be used for 100% Earth coverage (Figure 1). The original calculations showed that 77 such satellites would be needed (plus spares), so the system was named after element 77 on the periodic table (subsequent analysis showed that just 66 satellites were needed, but the re-naming it Dysprosium for the 66^th element was rejected). The satellites were arranged in six orbital planes of 11 satellites each and inclined at 86.4°, just a few degrees off a perfect north-south axis; these orbital planes criss-cross at each pole. At the height of 485 miles (781 km), each satellite orbits every 100 minutes, with a round-trip Earth-satellite link propagation delay of 5 msec, which is very acceptable for two-way speech.

These satellites were not just simple connecting points for one-hop, Earth-based connections between users. Instead, they were orbiting MTSOs which could dynamically link and unlink via the Ka microwave band (26.5 to 40 GHz) to any of four adjacent satellites: the ones immediately before and after in the same orbital plane, as well as the closest ones in adjacent planes (Figure 2). A call in progress might go through one, two, or more satellites and be handed off as the satellites orbited; these handoffs would occur every minute for a given call connection. As a result, a call’s link delay was just the 5 msec plus the satellite-to-satellite link delay of another few milliseconds, far less than the geosynchronous link with its 240-msec hop delay.

Figure 2: The satellites (green boxes) and their polar orbits (red lines) show the overlapping footprints of coverage each satellite provides as it illuminates a circular area of the Earth’s surface. (Image: SaVi satellite constellation visualization)

The fabric topology and software needed to make this work were unlike anything orbited. The processing and routing demands were stringent, yet available power was limited to the solar panels. The first-generation designs measured about 4 meters by 1.8 meters, weighed 689 kilograms (1,519 lb) with innovative antennas for communicating with ground stations as well as adjacent satellites (Figure 3). Due to the low orbits, the satellites were in Earth-circling radiation belts and needed radiation-hardened components, yet still would have reduced life.

2) Satellites alone were only part of the overall plan. Earth-based stations called gateways were needed to link to the 66 satellites and to each other, to complete the system management and fabric, and also link to the terrestrial phone network. These gateways (there were roughly two dozen), would be located around the globe, in countries that had a technology base and some that had nearly none.

The software needed to link these gateways and manage them in real-time, along with the actual links between them, was another high-risk challenge. Communication between satellites and earth stations used 30 GHz for the uplink and 20 GHz for the downlink. Some gateways were owned by the hosting country, while others were owned and operated by a private licensee in that country, with the government’s official approval. Overall system management was done by a dedicated Satellite Network Operating Center (SNOC) facility—also a major undertaking.

Figure 3: An Iridium satellite has standard solar panels for power but also carries two different sets of antennas: one for the ground up/downlink (above); the other for the link to adjacent satellites (below). (Image: Smithsonian Institution/National Air & Space Museum, PhoneIsMobile.com )

3) Finally, handsets had to be provided so users could actually contact the satellite constellation. Motorola contracted with several handset vendors, including Kyocera and their own handset group, to design and build these. The first units were relatively large and bulky (3 pounds), and priced at several thousand dollars, and subsequent units have shrunk considerably in size, weight and cost, and are now close but not quite to the parameters of concurrent, mass-market standard cell phones (Figure 4). Iridium phones have an unusual external antenna, which is a technical necessity for linking to the satellites. Some of the phones can even connect to a small, separate, domed-shaped antenna for a better signal.

Making it happen

The technical challenges across all three aspects – satellites, gateways, and handsets – were enormous, obviously. The design teams had to devise new topologies for these unique mesh networks, new algorithms for call handling and handoff, new RF designs including antennas, and make it all fit into the modest-size package.

Unlike conventional communications satellites, where each one is uniquely designed, built, and launched, a large number of Iridium satellites mandated a “mass production” approach. The idea was to build identical satellites in clusters of ten or more while only incorporating any changes in subsequent batches if there was a demonstrable benefit. Thus, Iridium standardized the satellites to the extent possible, which was a radical approach.

Figure 4: A fourth-generation handset, the model 9555 Iridium satellite phone handles voice and data; it is shown with its antenna extended for use. (Image: Iridium Communications Inc. via PhoneIsMobile.com)

The launches would be done from sites across the globe, including China, French Guyana, and the Soviet Union (before the breakup), using contracted services. A typical rocket would include at least six satellites, and sometimes up to a dozen, to save time and cost. While this provided many operational advantages, it also added risk, as when a rocket exploded or failed to orbit. The entire multi-satellite payload was lost (which happened several times).

While building identical units is not “mass-production” in the consumer-product world, it very much was for satellites, which, until that point, were unique, no-two-alike units. Note that the mass-production concept is now widely used, with the multiple satellite load and launch of hundreds and thousands of relatively small satellites (about 500 pounds/225 kilograms) in the StarLink system from SpaceX.

The other side of getting Iridium “off the ground” had little to do with technology and everything to do with spectrum assignment, regulatory issues, and global reach. The Motorola-driven Iridium system had to get some specific spectrum allocations from the International Telecommunication Union (ITU – the United Nations specialized agency for information and communication technologies) at its biannual meeting of over 100 countries, and also get license agreements with the countries that would host the gateways. Both allocation and agreements became extremely time-consuming and bureaucratic battles, as countries objected for security, financial, and political reasons.

In the end, what solved both the spectrum and gateway problems was a combination of Motorola’s long-standing relationships with key people in many of the countries, as well as promises and guarantees to gateway operators and their governments (and many rumors of “shady” payments and more). As a highly respected vendor for decades, Motorola’s local agents were able to actually call on key government ministries and officials, get their attention, and work out needed agreements.

The next part describes how Iridium soon failed as a business and how it came back from the nearly dead.

EE World Content

External References

“Eccentric Orbits: The Iridium Story,” John Bloom, Atlantic Monthly Press, 2016.
“Iridium Will Host Science Payloads,” IEEE Spectrum, Nov. 30, 2009
“The Collision of Iridium 33 and Cosmos 2251,”Aerospace, December 10, 2015
“A guide to useful, useless, official, and unofficial Iridium websites.”
“The Rise and Fall and Rise of Iridium,” Air & Space Magazine, September 2004
“Iridium ends legacy satellite service, switches all traffic to Next fleet,” Space News, February 2019
“SpaceX completes Iridium Next constellation,” Space News, January 11, 2019
“Iridium starting to deorbit legacy satellites as Next constellation comes online,” Space News, May 1, 2017
“Elon Musk’s Ambitious Communication Project to Ring Earth with 40,000 Satellites,” News18, Sept 19, 2020
Wikipedia, “Starlink”
“Starlink: SpaceX’s satellite internet project,” com, January 17, 2020
Thales Group, “Happy Birthday Iridium Next,” January 14, 2020
PhoneIsMobile, “Iridium Satellite Phone”
Wikipedia, “Iridium satellite constellation.”
Wikipedia, “Inmarsat”
Wikipedia, “Thuraya”
Wikipedia, “Globalstar”

Iridium global satcom system: Brilliant design, terrible business, last-minute reprieve, Part 1

November 3, 2020 By Bill Schweber Leave a Comment

This worldwide satellite-based communications system went from dream to reality in a decade but quickly failed in the market; its revival took persistence and luck, plus a new customer base.

Business failures of companies with grand schemes and grandiose plans are part of the realities of technology-driven visionaries. Sometimes, however, the project is so large and audacious that its evangelists misread harsh market realities despite astonishing technical success.

This was the case with the Iridium worldwide satellite-based communications system, a bold plan conceived in late 1987 by Bary Bertiger, Raymond J. Leopold, and Ken Peterson, engineers associated with Motorola (which holds the many Iridium patents). Though it is hard to put an exact price on the project, most estimates place the cost between $5 and $10 billion.

At the time, Motorola was among the worldwide leaders in wireless and wireless systems, providing basic voice radios, cellular infrastructure, and advanced systems to police, armed forces, and maritime users. They were a well-known, respected, and well-connected supplier in over 100 countries, with a reputation built over many decades. Without their financial investment and worldwide “influence,” Iridium would never have happened.

What Iridium is

Most people are so used to near-ubiquitous cellular connectivity that they may not fully realize that this is made possible by a cellular “backbone” network, which is invisible to the user. This network includes linked base stations and associated mobile telephone switching offices (MTSO) located as closely as needed to provide the cell coverage (a cell can range from a few blocks in span to tens of miles, depending on locale) (Figure 1). These MTSOs are linked to the base stations they directly serve and to each other and higher-level system management, usually via fiber-optic links or point-to-point microwave links, to manage and hand-off calls as the phone user moves from cell to cell.

The MTSO provides a critical behind-the-scenes function for the cellular phone system; it connects the nearby base stations to each other, to other MTSOs, and the existing landline telephone system. (Image: Tech-Faq)

The problem is that most of the Earth’s surface is covered with water and thus has no base stations or MTSOs; further, the maximum size of a base station is about 10 miles across (but many are far smaller, of course, and some are larger). There are also large, barely inhabited areas (the poles or deserts, for example), where base stations and MTSOs are not technically practical or financially viable; the Antarctic’s scientific stations are in this group.

The alternative to a cellular stem is conventional radio, but this has erratic connections due to atmospheric propagation issues, interference, electrical noise, and channel crowding due to too many users. Another possibility is a link to a geosynchronous satellite, but this has problems due to round-trip latency of about 250 msec and satellite visibility (which decreases as you get closer to either of Earth’s poles). There is a basic ship-to-shore radio and even a specialized satellite system (Inmarsat). Still, these are used primarily for low-rate weather updates, bulletins, or critical emergency messages, not ongoing, real-time conversations, and use carefully aimed dish antennas of about a meter diameter.

The Iridium system was designed to overcome all of the weaknesses of conventional radio, geosynchronous satellite links, geographical location, and travel while in use. The idea was to set up a system which would allow cellular-like connectivity (voice and even data) from anywhere on the globe—and they did mean anywhere.

The next part of this article looks at the plan and implementation of the Iridium system.

EE World Content

External References

“Eccentric Orbits: The Iridium Story,” John Bloom, Atlantic Monthly Press, 2016.
“Iridium Will Host Science Payloads,” IEEE Spectrum, Nov. 30, 2009
“The Collision of Iridium 33 and Cosmos 2251,”Aerospace, December 10, 2015
“A guide to useful, useless, official and unofficial Iridium websites”
“The Rise and Fall and Rise of Iridium,” Air & Space Magazine, September 2004
“Iridium ends legacy satellite service, switches all traffic to Next fleet,” Space News, February 2019
“SpaceX completes Iridium Next constellation,” Space News, January 11, 2019
“Iridium starting to deorbit legacy satellites as Next constellation comes online,” Space News, May 1, 2017
“Elon Musk’s Ambitious Communication Project to Ring Earth with 40,000 Satellites,” News18, Sept 19, 2020
Wikipedia, “Starlink”
“Starlink: SpaceX’s satellite internet project,” com, January 17, 2020
Thales Group, “Happy Birthday Iridium Next,” January 14, 2020
PhoneIsMobile, “Iridium Satellite Phone”
Wikipedia, “Iridium satellite constellation”
Wikipedia, “Inmarsat”
Wikipedia, “Thuraya”
Wikipedia, “Globalstar”

What is the HART protocol?

November 3, 2020 By Nikhil Agnihotri Leave a Comment

Data communication over analog signals is a common process. In automation, the data is communicated to and from controllers with several different process instruments. Quality is important as the controllers and smart instruments must communicate over long distances.

Additionally, the data communication between a device and a controller must be dictated by a protocol (i.e. a set of digital message formats and rules). Many communication protocols are used in industrial automation, including As-i, BSAP, CIP, CAN bus, DeviceNet, DirectNet, EtherCAT, EtherNet/IP, EGD, Powerlink, HART, Interbus, Modbus, OSGP, Profibus, MPI, and others.

The HART (highway addressable remote transducer) protocol is one of the most popular for use in industrial automation. Based on the legacy 4-20mA analog instrumentation wiring, the HART protocol uses a pair of wires for data communication between industrial controllers and smart process instruments.

Understanding analog transmission
Computer systems and interfaces use digital voltage signals for data communication. The problem with voltage signals, however, is that they’re affected by wire resistance — which makes communicating voltage signals for data communication over long distances impractical. This is why current loops are typically used in automation.

Since the ‘80s, the 4-20 mA has been the de facto standard in automation wiring. The value of the 4 mA represents a “live zero,” helping maintain a minimum amount of current for the loop-powered instruments.

These current loops use analog (continuous) signals for data communication. The digital data is superimposed on a carrier signal (current) using a digital modulation technique. The amplitude-shift keying (ASK), frequency-shift keying (FSK), and quadrature phase shift keying (QPSK) are currently the most commonly used digital modulation techniques.

Understanding the HART protocol
The highway addressable remote transducer or HART is an industrial automation protocol. It’s a global standard for two-way analog communication between smart-process instruments and control or monitoring host systems.

The host system can be a laptop, a handheld device, or an industrial process-control system (PLC/DCS). The protocol is based on the Bell 202 standard and it’s capable of superimposing digital information on the conventional 4-20 mA analog signals using the FSK. This protocol is also maintained by the HART Communication Foundation (HCF) and defines physical connectivity, as well as the commands used by applications.

The HART protocol communicates data at 1200 bps allowing a host to get at least two updates from a smart-field device in one second. The protocol provides two simultaneous channels:

1. The 4-20 mA analog signal – for communicating primary measured values
2. A digital signal that’s superimposed on the analog signal – for communicating additional information

As the FSK signals have an average value of zero, the modulation does not interrupt the carrier analog signal.

The HART is a master-slave protocol that allows data communication in point-to-point or multi-drop mode. Up to two masters (in point-to-point configuration) can share the communication bus, simultaneously. This permits handheld communicators to operate as secondary masters while a control or monitoring system operates as the primary master.

How the HART protocol works
The HART protocol makes use of the FSK. The digital data is represented by two different frequencies. The frequency of 1,200 Hz represents bit 1 and 2,200 Hz represents bit 0.

By superimposing two frequencies of direct-current analog signals, the HART provides simultaneous analog and digital communication. The 4-20 mA signal is not affected by the digital modulation.

For this reason, the HART is called a hybrid protocol.

The HART is a master-slave protocol and the entire data communication process is initiated and controlled by the host system. It’s the host device that requests the data from a HART-enabled field device. This field device simply responds to the HART commands according to the protocol.
The HART protocol operates over two wires allowing for 2-way communication between the host controller and the field devices.

There are also wirelessHART solutions available. However, the wirelessHART gateways do not use an analog signal for data transmission. Instead, they use the digital parameters over a wireless carrier wave.

The HART network
HART-enabled devices can operate in one of the two configurations:

Point-to-point: when the HART communication occurs between a HART-enabled device and a host system. The primary variable (data) is communicated over an analog signal and all additional variables are communicated using a digital signal. The host system can include up to two masters: a primary and a secondary master.
Multi-point: when multiple HART-enabled devices are connected in parallel to a transmission line. According to the HART v07, 64 field devices can be connected to a HART bus in a multi-drop configuration. These devices use only digital channels for data communication while the analog signal is maintained fixed to the 4 mA. Each device has a unique HART address and no two devices can access the transmission line simultaneously.

The HART protocol
The data in a HART protocol is transmitted in packets. Each message packet contains the following data fields:

Preamble – includes 5 to 20 bytes with the hex value, “FF,” which is transmitted from the host system to the field device(s). Most of the host systems only transmit five preamble bytes. These bytes are transmitted to help the field device synchronize with the data stream.

Start character – after the preamble bytes, a start byte is transmitted from the master (host) to the field device. This byte can indicate one of several values and, often, contains the master number. The start character is the indicator of the beginning of the HART packet.

Aside from the master number, it may contain indicators for the:

Message format – such as the master-to-slave, slave-to-master, or the burst message from a slave
Address format – a short or long frame
Number of bytes in the expansion field

Address – may have 1 to 5 bytes. It contains both a master and a slave address. The indication for the master address is a single bit, where 1 indicates a primary master and 0 indicates a secondary master. The indication of a slave address is a 4-bit polling address in a short frame and a 38-bit unique identifier in the long frame. One bit is used to indicate the burst mode from the slave.

Expansion – may contain 0 to 3 bytes. The number of bytes in an expansion field includes bits 5 and 6 of the start character.

Command – has a single byte that contains a HART command.

The universal HART commands range from 0 to 30
The practice commands range from 32 to 126
The device-specific commands range from 128 to 253

From the HART v06 onwards, the 16bit extended commands for the device families are also supported. These commands begin with the 0x1F as a command byte, followed by a 2-byte command.

Byte count – has a single byte indicating the number of bytes in the status and data fields. It let the receiver field device know when the message packet ends.

Status – is only present in the messages transmitted from a slave to the master. It contains two bytes indicating communication errors, the status of a received command, or the status of the receiver field device.

Data – may contain 0 to 255 bytes. The presence of the data field depends on a particular command. All universal and common practice commands have 33-byte data fields.

Checksum – a HART message will end with a checksum byte. It’s the XOR of all the previous bytes. To detect a communication error, a parity bit is attached to each byte. The checksum byte helps in maintaining the overall integrity of the HART message.

The HART modes

The HART protocol can operate in two modes:

Master-slave mode: where the host system initiates and controls the entire data communication. There can be two masters, including the primary and secondary ones in the HART loop.The primary master can be a distributed control system (DCS), a programmable logic controller (PLC), or a workstation. The secondary master can include handheld communicators or a laptop/PC. The slave devices can be HART-enabled sensors, actuators, controllers, or transmitters.
Burst mode: only available in a point-to-point configuration. In this mode, the slave device continuously broadcasts the standard HART reply messages to the master(s).Once a master instructs the slave device to broadcast the messages, the slave keeps sending responses without the need for polling. It stops only when it receives further instructions from the host system. This is why this mode allows for faster data communication with up to 3 or 4 updates per second.

The HART applications
When using the HART protocol, four or more variables can be transmitted in a single message. Multi-variable instruments can take the most advantage of this protocol. In fact, there are now millions of HART-enabled devices that are used in process automation and other industrial applications.

There are also more than 250 member companies of the HART Communication Foundation that have their HART-enabled products in the market. Several of these products are used in DCS and PLC applications.

As the HART uses the older 4-20 mA standard, it has become the de facto standard for data communication for smart-field devices and grid instrumentation. Smart-field devices and sensors use this protocol for communicating device configuration, diagnostic data, device status, device troubleshooting, and measurement values.

The wirelessHART is also widely used in instrumentation and automation. It allows for the communication of sensor data without complex multiplexing and cable installations.

Device descriptions
Generally, host systems use high-level language applications for data communication when using the HART protocol. The protocol is implemented by software on the host device. Since the host system might need to communicate with several different HART devices, the software must “know” the HART commands supported by a particular device.

Similar to how computer peripherals have device drivers written for them to communicate with different computer systems, HART devices have device descriptions (DD).

The device descriptions are written in the HART device description language (DDL) and their source files are submitted by the device manufacturer to HCF for registration in the HCF DD library. After verification, these source files are available for host applications.

The host applications use these DD files to identify common practice and device-specific commands supported by a particular device. By using DDs, the host suppliers need not build custom interfaces and drivers for every different HART device.

The pros and cons
The HART protocol offers many advantages in automation and instrumentation segments. Perhaps the greatest one is that it’s based on the conventional 4-20 mA standard. This reuse of the 4-20 mA wiring not only means the protocol is cost-effective, but it also allows it to have wide acceptance among industrial manufacturers and vendors.

Today, there’s a broad selection of HART products available with compatible host applications and devices. The protocol is highly accurate, reliable and it’s platform-independent — allowing for full-interoperability in a multi-vendor environment. As a hybrid protocol, it’s also the preferred choice for multi-variable instruments. Thanks to its ability to self-diagnosis with quick device configuration, the HART protocol is now commonly used with smart-field devices.

There are some limitations, however. For example, the digital signal in the HART transmission is relatively slow. Also, for a multi-drop configuration, the analog signal is not available and the number of devices that can share the transmission line is limited. These limitations often mean integration with other protocols and standards is necessary.

Quantum compasses and optical imaging for global positioning and navigation

October 27, 2020 By Jeff Shepard Leave a Comment

There is an emerging demand for a replacement for today’s global navigation satellite systems (GNSS), and especially for the global position system (GPS) in the U.S. Part one of this three-part FAQ series presented several of the shortcomings of today’s GPS technology and some efforts to augment it and improve its performance. Part two presented a terrestrial-based technology that is already being offered as a substitute for GPS in many applications. This third and final installment looks into the future at possible quantum-based and optical-based position, navigation, and timing (PNT) technologies that could eliminate the need for GPS devices.

Close-up of a quantum accelerometer (Image: Imperial College London)

The next generation of inertial sensors may be based on a compact gyroscope and a three-axis accelerometer using new techniques in atom interferometry. Called a quantum compass, it is an instrument that measures relative position using the technique of atom interferometry. It includes an ensemble of accelerometers and gyroscope based on quantum technology to form an inertial navigation unit.

A quantum compass contains clouds of atoms frozen using lasers. By measuring the movement of these frozen particles over precise periods of time, the device’s motion can be calculated. The device would then provide a tamper-proof accurate position in circumstances where satellite navigation is not possible.

The ultimate goal is to build a new autonomous device that can compete with technologies based on global positioning systems without external communication drawbacks for recalibration. The device would then provide a tamper-proof accurate position in circumstances where satellites are not available for satellite navigation, e.g., a fully submerged submarine.

AIG’s (atomic interferometer gyroscopes) and ASGs (atomic spin gyroscopes) use an atomic interferometer to sense rotation or, in the latter case, uses atomic spin to sense rotation with both having a compact size, high precision, and the possibility of being made on a chip-scale. AIGs may compete, along with ASGs, with the established ring laser gyroscope, fiber optic gyroscope, and hemispherical resonator gyroscope in future inertial guidance applications.

The UK’s first quantum accelerometer for navigation has been demonstrated by a team from Imperial College London and M Squared. M Squared developed a universal laser system for cold atom-based sensors that the company has already implemented in a quantum gravimeter. That laser is now also used in the quantum accelerometer built in collaboration with Imperial. Combining high power, exceptionally low noise, and frequency tunability, the laser system cools the atoms and provides the optical ruler for the acceleration measurements.

The quantum accelerometer relies on the precision and accuracy possible by measuring properties of supercool atoms. At extremely low temperatures, the atoms behave in a ‘quantum’ way, acting like both matter and waves. The current system is designed for the navigation of large vehicles, such as ships and submarines. Smaller systems are envisioned in the future.

In France, the joint laboratory iXAtom brings together the knowledge of the French company iXblue — experts in optical gyroscopes, photonics, and inertial navigation — and personnel from LP2N specialized in atom interferometry. This collaboration aims to make technological advances using cold atoms to develop the next generation of inertial sensors for industrial, military, and Space applications, with anticipated improvements in their performance.

Cold-atom quantum accelerometer simplified schematic (Image: iXAtom)

In the near future, iXAtom plans to develop a compact gyroscope and a three-axis accelerometer based on new techniques in atom interferometry. The ultimate goal of iXAtom is to build a new autonomous device that can compete with technologies based on global positioning systems without the drawback of external communication for recalibration.

Optical navigation using terrestrial objects

Optical navigation using terrestrial landmarks and mapping has been under development for many years. Terrain Contour Matching, or TERCOM, was a navigation system used primarily by early versions of cruise missiles. It uses a pre-recorded contour map of the terrain compared with measurements made during flight by an on-board radar altimeter. A TERCOM system considerably increases the accuracy of a missile compared with inertial navigation systems (INS). The increased accuracy allows a TERCOM-equipped missile to fly closer to obstacles and generally lower altitudes, making it harder to detect by ground radar.

The limited data storage and computing systems of the time meant that the entire route had to be pre-planned, including its launch point. If the missile was launched from an unexpected location or flew too far off-course, it would never fly over the features included in the maps and would become lost.

DSMAC was an early form of artificial intelligence (AI) that could guide missiles in real-time by using camera inputs to determine location. DSMAC was used in Tomahawk Block II onward and proved itself successfully during the first Gulf War. The system worked by comparing camera inputs during the flight to maps computed from spy satellite images. The DSMAC AI system computed contrast maps of images, combined in a buffer, and then averaged. It then compared the averages to stored maps computed beforehand by a large mainframe computer, which converted spy satellite pictures to simulate what routes and targets would look like from a low level.

DSMAC automatic target recognition (ATR) machine learning (ML) flow chart. (Image: Wikipedia)

An example of a detection algorithm is shown in the flowchart above. This method uses M blocks of data, extracts the desired features from each then models them using a Gaussian mixture model (GMM). After a model is obtained using the data collected, conditional probability is formed for each target in the training database. This method can distinguish between vehicle types (wheeled vs. tracked vehicles, for example).

Since the data was not identical and would change by season and from other unexpected changes and visual effects, the DSMAC system within the missiles had to compare and determine if maps were the same, regardless of changes. It could successfully filter out differences in maps and use the remaining map data to determine its location. Due to its ability to visually identify targets instead of simply attacking estimated coordinates, its accuracy exceeded GPS guided weapons during the first Gulf War.

ImageNav™, developed by Scientific Systems for the US Air Force, is a modern optical navigation system for aircraft. ImageNav is a non-GPS precision navigation software that uses inertial navigation system information to match onboard camera imagery, including electro-optical and infra-red, against stored geo-registered digital terrain elevation data (DTED) to determine the precise location of an air vehicle in flight. It has a terrain database of the area being navigated and matches it with input from video cameras to work out its location.

ImageNav software is multi-threaded and scalable to run on multiple cores. ImageNav uses time-synchronized camera imagery and can accept PGM or PNG images up to 1024×1024 pixels in size and at up to 30 frames per second. ImageNav has been successfully tested on a number of aircraft but could also find uses in self-driving vehicles.

High Tech Celestial Navigation

Mariners have used various celestial navigation techniques since ancient times. Two stars, the local altitude, and a clock are all that’s needed to determine a position using a sextant. Celestial navigation can be surprisingly accurate; if the values are determined to within 1 arc minute, the possible error is about 1 nautical mile, but if the values can be determined to within 1 arc second, the possible error drops to about 30 meters. Today’s advanced optics and high-speed microelectronics can enable celestial navigation with an accuracy of 15 meters, without the need to know the altitude, even in a moving aircraft or missile.

Tracking fast-moving satellites like the International Space Station has helped to improve the accuracy of celestial navigation. Having large numbers of fast-moving objects to get bearings on means that the system, called Skymark, can achieve greater accuracy than slow-moving stars. Skymark uses a database of visible satellites – both working satellites and space junk – and has a claimed accuracy of 15m (49ft), making it almost as good as GPS. And it uses a proprietary stellar horizon refraction algorithm that eliminates the need for a local vertical. Its accuracy depends on knowledge of the atmospheric density profile to provide a refraction estimation that replaces the vertical measurement in earlier celestial navigation systems.

Skymark can correct an emerging problem common to inertial navigation systems when access to GPS is denied: they tend to drift and lose accuracy over time, making them inadequate on their own for long-distance navigation. Skymark provides a system position fix through a unique combination of advanced optics, sensors, and algorithms to triangulate off of known positions of stars and satellites.

Today’s GPS is several decades old. It has received numerous upgrades, and completely new third-generation satellites are currently being launched. However, there’s growing concern that the system may be reaching the limits of its usefulness. To learn more about the limitations of GPS and what is being done to address those limitations, you might enjoy reading part one of this FAQ series, “GPS is a ubiquitous and problematic technology,” and part two, “eLORAN a terrestrial alternative to GPS.”

References:

Automatic target recognition, Wikipedia
ImageNav, Scientific Systems
iXAtom – LP2N and iXblue Cold Atoms joint laboratory, iXAtom
Quantum ‘compass’ could allow navigation without relying on satellites, M Squared
TERCOM, Wikipedia

Teardown: Cisco Explorer 8642HDC high-definition DVR with multi-stream cableCARD interface

October 26, 2020 By Lee Teschler Leave a Comment

The Covid-19 pandemic has forced many people to spend more time in front of a TV set. Here’s a look at what’s inside the cable box responsible for a large portion of home entertainment.

Examine the hook-up for many cable TV customers and you’ll likely find something like the Cisco Explorer 8642HDC DVR. This set-top box has been out for several years, long enough for numerous examples of it to show up on eBay. So during one of our recent work-from-home sessions, we had the opportunity to disassemble and dissect one.

The only difficulty in getting at the internals of the DVR were the security screws holding the case together. The security is more apparent than real in that the security torx heads necessary to do the job are readily available on Amazon.

DVR exposed — Click image to enlarge. With the case off, the Seagate drive and CableCARD become visible. Also interesting is the size of the heat sink on one of the ST Microelectronics private-label chips.

The first two things prominently visible when the covers come off are the Seagate 320 GB hard drive, used to hold Mork and Mindy reruns or other paraphernalia recorded by the user, and a Multi-Stream CableCARD assembly. This assembly is as good a place as any to begin the description of the DVR circuitry.

The physical CableCARD is a business-card-sized PCB that is inserted into a slot in the DVR. It serves to identify and authorize the customer and decodes the encrypted digital cable signal. Once the card has decrypted the signal, it provides an MPEG-2 transport stream to the DVR. The card also receives messages sent over the out-of-band signaling channel by the cable company and forwards them to the DVR. (As an aside, higher end TVs sometimes come with a cable tuner built in and include a slot for a CableCARD. As in a DVR, the card unlocks the channels and services to which the cable customer subscribes. TVs that support CableCARD this way are generally labeled “digital cable ready,” DCR.)

The CableCARD in this DVR contains four ICs, a 64 Mb SDRAM, a Spansion NOR flash, a proprietary media processor made by ST Microelectronics, and a 32-Bit MCU from Infineon. The Infineon MCU is a variant of the SLE 88 Family, tailored for high-end security applications, particularly those in pay TV. Basically the card takes encrypted signals received by the DVR tuner, unencrypts them, and sends the resulting compressed audio/video (MPEG) signal back to the DVR for further processing. It is labeled as a multi-stream device, meaning it can decode two channels simultaneously—necessary for, say, watching one channel while recording another.

The cable signal goes through a lot of processing before it ever gets to the CableCARD. Starting at the cable input connector, the signal first goes through a Macom diplexer. The diplexer sends the incoming cable signal to a Skyworks active splitter (APS3606) which converts the signal into three RF signals that go to video tuner stages.

PCB with callouts — The interesting ICs on the DVR board. Not shown: One private-label device on the opposite side. Click image to enlarge.

The diplexer also allows an Analog Devices cable line driver (AD8324) to exchange information with the service provider via the cable wire. This is how your cable company knows that, for example, your DVR is one of theirs and not some pirate device. This is basically an Ethernet signal. It comes from two chips made by Entropic, a coaxial network controller (EN2210) and a coaxial network interface (EN1010). The network interface chip sits in its own shielded enclosure.

Data for the Ethernet connection seems to be handled by an Analog Devices analog front-end chip (AD9969JSTZ). There’s not much information available about this device other than that it contains two 12-bit and one 10-bit ADCs along with a 14-bit DAC.

The other output of the diplexer gets sent to three Microtune broadband tuners, each sitting in separate shielded areas on the PCB. These tuners (MT2022) each produce an IF in the 30 to 57 MHz range. These separate tuner stages are what let cable viewers record one channel while watching another—the DVR tunes to the channels of interest and uses the Microtune ICs to send the programming signals to demodulators. Two of the tuners are for displaying/recording while the third is for data networking. (This setup also illustrates why it would be tough to field a DVR handling more than two TV channels simultaneously; the tuner circuit for each channel takes up almost 3 in2 of PCB space. It would be tough to squeeze another tuner onto this architecture.)

The bulk of the signal processing and decoding takes place via private-label custom ASICs from ST Microelectronics. There are two custom ICs on the top of the PCB, one on the bottom. All seem to be from ST Micro. One of the ASICs apparently works pretty hard—it contains a beefy heat sink. These chips would necessarily handle the QAM demodulation, MPEG decoding, as well as other video processing and modem functions.

You can get an idea of some of the functions these chips handle from commercial versions. One is the STiH412 from ST Microelectronics. It contains a dual-core ARM CPU and a quad-core GPU and is designed to decode ultra HD.

The DVR’s VFD front panel is controlled by another ST Micro device (STM86312). An interesting point is that the DVR doesn’t contain a chip handling the IR signals from the remote. This leads us to surmise that one of the proprietary media processors assumes these chores directly.

The power supply section of the board is built around a Texas Instruments triple synchronous buck chip (TPS5130) so named because it converts 5.5 V into three other voltages. Some power FETs from ON Semiconductor comprise the other ICs in the power circuit.

Three other ICs round out the interesting part of the DVR circuit. A Cirrus CS4352 DAC/line driver puts out stereo audio for the speaker outputs. A Texas Instruments serial bus transceiver (TSB41AB1) sits underneath the CableCARD assembly and likely handles the communication between the card and the rest of the DVR.

Finally, a Texas Instrument TPS2041B power distribution switch sits next to the CableCARD assembly. TI says this chip is intended for applications where heavy capacitive loads and short circuits are likely to be encountered. It basically limits its output current when it senses a too-heavy load. Going by a reference design published by TI, this is probably part of the USB circuit.

And that’s about it for the Cisco DVR. Thanks for watching.

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Teardown: Cisco Explorer 8642HDC high-definition DVR with multi-stream cableCARD interface

The Covid-19 pandemic has forced many people to spend more time in front of a TV set. Here’s a look at what’s inside the cable box responsible for a large portion of home entertainment.

EE World Online Network

Microcontroller Tips

FAQ

Microcontroller power requirements

Arduino power requirements

Example: Arduino Pro Mini

Power source line loss

Contact resistance

Single supply choice – varied distances?

Arduino power source options

VIN pin, properly used

The Covid-19 pandemic has forced many people to spend more time in front of a TV set. Here’s a look at what’s inside the cable box responsible for a large portion of home entertainment.

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EE World Online Network

Microcontroller Tips

V_IN pin, properly used