BLDC Fan Current

Motors and Measurements

Today’s small fans and blowers depend on brushless DC (BLDC) motor technology for their operation. Here, Ed explains how these seemingly simple devices are actually quite complex when you measure them in action.

By Ed Nisley

The 3D printer Cambrian Explosion unleashed both the stepper motors you’ve seen in previous articles and the cooling fans required to compensate for their abuse. As fans became small and cheap, Moore’s Law converted them from simple DC motors into electronic devices, simultaneously invalidating the assumptions people (including myself) have about their proper use.

In this article, I’ll make some measurements on the motor inside a tangential blower and explore how the data relates to the basic physics of moving air.

Brushless DC Motors

Electric motors, regardless of their power source, produce motion by opposing the magnetic field in their rotor against the field in their stator. Small motors generally produce one magnetic field with permanent magnets, which means the other magnetic field must change with time in order to keep the rotor spinning. Motors powered from an AC source, typically the power line for simple motors, have inherently time-varying currents, but motors connected to a DC source require a switching mechanism, called a commutator, to produce the proper current waveforms.

Mechanical commutators date back to the earliest days of motor technology, when motors passed DC power supply current through graphite blocks sliding over copper bars to switch the rotor winding currents without external hardware. For example, the commutator in the lead photo switches the rotor current of a 1065 horsepower marine propulsion motor installed on Fireboat Harvey in 1930, where it’s still in use after nine decades.

Fireboat Harvey’s motors produce the stator field using DC electromagnets powered by steam-driven exciter generators. Small DC motors now use high-flux, rare-earth magnets and no longer need boilers or exhaust stacks.

Although graphite sliding on copper sufficed for the first century of DC motors, many DC motors now use electronic commutation, with semiconductor power switches driven by surprisingly complex logic embedded in a dedicated controller. These motors seem “inside out” compared to older designs, with permanent magnets producing a fixed rotor field and the controller producing a time-varying stator field. The relentless application of Moore’s Law put the controller and power switches on a single PCB hidden inside the motor case, out of sight and out of mind.

Because semiconductor switches eliminated the need for carbon brushes, the motors became known as Brushless DC motors. Externally, they operate from a DC supply and, with only two wires, don’t seem particularly complicated. Internally, their wiring and currents resemble multi-phase AC induction motors using pseudo-sinusoidal stator voltage waveforms. As a result, they have entirely different power supply requirements.

The magnetic field in the rotor of a mechanically commutated motor has a fixed relationship to the stator field. As the rotor turns, its magnetic field remains stationary with respect to the stator as the brushes activate successive sections of the rotor winding to produce essentially constant torque against the stator field. Electronically commutated motors must sense the rotor position to produce stator currents with the proper torque against the moving rotor field. As you’ll see, the motor controller can use the back EMF generated by the spinning rotor to determine its position, thereby eliminating any additional components.

Figure 1
The blower motor current varies linearly with its supply voltage, so the power consumption varies as the square of the voltage. The motor speed depends on the balance between torque and load.

I originally thought Brushless DC (BLDC) motors operated much like steppers, with the controller regulating the winding current, but the switches actually regulate the voltage applied to the windings, with the current determined by the difference between the applied voltage and the back EMF due to the rotor speed. The difference between current drive and voltage drive means steppers and BLDC motors have completely different behaviors.

Constant Voltage Operation

The orange trace along the bottom of Figure 1 shows the current drawn by the 24 V tangential blower shown in Figure 2, without the anemometer on its outlet, for supply voltages between 2.3 V and 26 V. The BLDC motor controller shapes the DC supply voltage into AC waveforms, the winding current varies linearly with the applied voltage and, perhaps surprisingly, the blower looks like a 100 Ω resistor.

Figure 2
An anemometer measures the blower’s outlet air speed and a square of retroreflective tape on the rotor provides a target for the laser tachometer. If you are doing this in a lab, you should build a larger duct with a flow straightener and airtight joints.

The blower’s power dissipation therefore varies as the square of the supply voltage, as shown by the calculated dots in the purple curve. In fact, the quadratic equation fitting the data has 0.00 coefficients for both the linear and constant terms, so it’s as good as simple measurements can get.

As you saw in March (Circuit Cellar #332) and May (Circuit Cellar #334), a stepper motor driven by a microstepping controller has a constant winding current and operates at a constant power. Increasing the supply voltage increases the rate of current change but, because the controller applies the increasing voltage with a lower duty cycle, it doesn’t directly increase power dissipation. …

Read the full article in the July 336 issue of Circuit Cellar

Don’t miss out on upcoming issues of Circuit Cellar. Subscribe today!

Note: We’ve made the October 2017 issue of Circuit Cellar available as a free sample issue. In it, you’ll find a rich variety of the kinds of articles and information that exemplify a typical issue of the current magazine.

Deadline Extended to June 22 — Vote Now!

UPDATE: We’ve extended our 2018 reader survey on open-spec Linux/Android hacker boards through this Friday, June 22.   Vote now!

Circuit Cellar’s sister website has launched its fourth annual reader survey of open-spec, Linux- or Android-ready single board computers priced under $200. In coordination with, LinuxGizmos has identified 116 SBCs that fit its requirements, up from 98 boards in its June 2017 survey.

Vote for your favorites from LG’s freshly updated catalog of 116 sub-$200, hacker-friendly SBCs that run Linux or Android, and you could win one of 15 prizes.

Check out LinuxGizmos’ freshly updated summaries of 116 SBCs, as well as its spreadsheet that compares key features of all the boards.

Explore this great collection of Linux SBC information. To find out how to participate in the survey–and be entered to win a free board–click here:




Cellular/Wi-Fi Gateway Targets In-Vehicle Intelligent Systems

Kontron has introduced the EvoTRAC G103 In-Vehicle Rugged Cellular and Wi-Fi Gateway that provides broad connectivity capabilities that enable a new range of in-vehicle management, remote access and cloud-based applications. Providing the mobile connectivity and onboard recording device storage needed for a new generation of more intelligent systems, the EvoTRAC G103 features a WiFi and 4G Advanced Pro+ LTE module, and includes 64 GB eMMC for onboard storage as well as optionalfixed storage capacity.

The EvoTRAC G103 is a flexible open-architecture building block platform that supports fast access to actionable information from its integrated dual Gigabit Ethernet and dual CAN bus interface that supports 2.0 A and B, along with two USB 2.0 interface. With the explosion of data generated by today’s commercial vehicles, implementing a robust gateway such as the EvoTRAC G103 offloads important information operators can use to keep drivers safe, lower fuel consumption and effectively manage maintenance costs.

Tested to survive extreme temperature (-40° C to +80° C) and other demanding on and off-road vehicle conditions (shock, vibration, humidity, salt fog), the EvoTRAC™ G103 Gateway leverages Kontron’s hardened Type 6 COMe E3845 COM Express® CPU module coupled with a ruggedized Carrier Board, all packaged in a natural convection, sealed IP67 enclosure. Extremely rugged and mechanically compact, this gateway is based on the efficient, low-power Intel Atom processor, and incorporates protection from water and dust ingress, as well as CISPR25 emissions and ISO 11452-2 susceptibility.

Kontron |

U-Blox Modules Selected for IoT Development Board Pair

U‑blox has announced that its modules will be at the core of two new developer boards. The boards, which are designed and produced by Seeed, one of China’s largest distributors of microelectronic components for the international developer and maker communities, deliver cellular communication and positioning capabilities for a wide range of applications in the IoT

The first of the two development boards is a Raspberry Pi HAT designed to augment Raspberry Pi computers with cellular communication as well as cellular‑based positioning services. The board will be released in multiple variants (USA AT&T, USA Verizon, Europe) based on the u‑blox LARA‑R2 LTE Cat 1 module series.
The second board, the WIO LTE Cat M1 / NB1 tracker, provides the essential hardware to make low‑power location tracking devices for people, pets, and assets. It can be programmed using the Arduino IDE and is also Espruino (JavaScript) compatible. The board uses the u‑blox MAX‑M8Q GNSS module to determine position, integrating signals from multiple GNSS satellite constellations, and connects to the cellular network using the u‑blox SARA‑R4 LTE Cat M1 / NB1 module. Developers and businesses can customize the standalone board and have it manufactured through Seeed’s services to create solutions tailored to their specific needs.

U-blox |

Nordic BLE SoC Selected for Cloud-Connected Thermostat

Nordic Semiconductor has announced that Sikom, a developer of GSM-based IoT platforms, employs Nordic’s nRF52840 Bluetooth 5/Bluetooth Low Energy (Bluetooth LE) advanced multiprotocol System-on-Chip (SoC) in its ‘Bluetooth Thermostat EP’ to support smartphone connectivity and smart-home networking. The thermostat is available to consumers and OEMs developing their own heating control systems.

The Nordic SoC’s Bluetooth 5 long-range capability enhances connection stability, boosting range, and allowing the thermostat to be configured and controlled from anywhere in the house. From a companion app on a Bluetooth 4.0 (and later) smartphone the user can control thermostat features such as comfort and economy temperature set points, week programs, vacation modes and temperature logs.

Because the thermostat can be controlled and configured directly from the smartphone, there is no requirement for a proprietary gateway between mobile device and thermostat, lowering the cost and complexity of installation and setup. In addition, the thermostat’s Bluetooth 5 connectivity enables it to join a Sikom smart-home network and communicate directly with other wireless devices to support advanced features such as power control and limiting. The thermostat also integrates with 4G/LTE (cellular) technology to enable remote control via Sikom’s Cloud platform.

Enabled by the nRF52840 SoC’s 32-bit Arm Cortex M4F processor, 1 MB Flash memory, and 256 KB RAM, the Bluetooth Thermostat EP platform can support a variety of complex remote thermostat/heating applications. The processor has ample power to run the Bluetooth 5 RF software protocol (“stack”) and Sikom’s application software and bootloader. The SoC also supports Over-the-Air Device Firmware Updates (OTA-DFU) for future improvements.

Nordic’s nRF52840 Bluetooth 5/Bluetooth LE SoC is Nordic’s most advanced ultra low power wireless solution. The SoC supports complex Bluetooth LE and other low-power wireless applications that were previously not possible with a single-chip solution. The SoC combines the Arm processor with a 2.4 GHz multiprotocol radio architecture featuring -96dB RX sensitivity and an on-chip PA boosting output power to a maximum of 8 dBm. The SoC is supplied with the S140 SoftDevice, a Bluetooth 5-certified stack which supports all the features of the standard and provides concurrent Central, Peripheral, Broadcaster and Observer Bluetooth LE roles.

Nordic Semiconductor |


Verizon Certifies Several Telit LTE Modules

Telit has announced that Verizon has certified several of its LTE products. The seven modules are part of Telit’s portfolio of LTE Cat M1, Cat 1, Cat 4 and Cat 11 products, with the LE910-SV V2 and LE910B1-NA modules that also supports Verizon’s Voice over LTE (VoLTE) technology. The modules are now available for operation on Verizon’s 4G LTE network. The following modules are included: ME910C1-NV LTE Cat M1 module, LE910-NA V2 LTE Cat 4 module, LE910-SV V2 LTE Cat 4 VoLTE module, LE910B1-NA LTE Cat 1 VoLTE module, ME866A1-NV LTE Cat M1 module, LE866-SV1 LTE Cat 1 module and LM940 LTE Cat 11 mini PCIe module.
The ME910C1-NV, LE910-SV V2 and LE910-NA V2 modules are members of Telit’s xE910 family (shown). And the LE866-SV1, one its xE866 family, is one of the smallest cellular modules in the market.  Any of the modules can be applied as drop-in replacements in existing devices based on the families’ modules for 2G, 3G and the various categories of LTE. With Telit’s design-once-use-anywhere philosophy, developers can cut costs and development time by simply designing for the xE910 or xE866 LGA common form factors, giving them the freedom to deploy technologies best suited for the application’s environment.

Integrators and providers looking for lower costs, more security and extended product lifecycles now have more options with Telit’s Verizon-certified LTE and VoLTE modules. Telit’s certified modules may be used by its customers in segments like telematics, home and business security, person and asset tracking, wellness monitoring for the elderly and convalescent, smart home and smart buildings.

The LM940 module boasts a power-efficient platform and is the ideal solution for commercial and enterprise applications in the network appliance and router industry, such as branch office connectivity, LTE failover, digital signage, kiosks, pop-up stores, vehicle routers, construction sites and more. This module includes Linux and Windows driver support.

Telit |

Development Tool Speeds IoT Sensor Design

STMicroelectronics offers a tool called AlgoBuilder designed to take the coding out of firmware development by letting users build sensor-control algorithms graphically with library modules, ready to compile and run on an STM32 microcontroller.

Created to simplify development of IoT devices containing ST’s MEMS sensors and MCUs, AlgoBuilder helps quickly get a proof-of-concept model up and running. Users can build their algorithms quickly and intuitively by dragging and dropping selected functions, connecting the blocks, and configuring properties. AlgoBuilder validates all design rules and automatically generates C code based on the graphical design.
AlgoBuilder provides libraries such as logic and mathematical operators, signal processing, user inputs, vector operations, and many others. Turnkey algorithms for commonly used functions such as sensor hub, motion-sensor calibration, activity recognition, motion intensity, and pedometer are included. Users can also add their own custom functions to the AlgoBuilder libraries.

AlgoBuilder provides an environment for connecting them with other logic to create a complete firmware project ready to compile using an STM32 IDE (Integrated Development Environment) such as TrueSTUDIO for STM32, SW4STM32 System Workbench for STM32, IAR-EWARM IAR Embedded Workbench for Arm and Keil µVision MDK-ARM-STM32.

AlgoBuilder can generate firmware for deployment on various STM32 platforms. These include the NUCLEO-F401RE and NUCLEO-L476RG development boards with the X-NUCLEO-IKS01A2 MEMS-sensor expansion board, and ST’s SensorTile IoT module. The SensorTile integrates a STM32L476JG ultra-low-power MCU, motion and environmental MEMS sensors and Bluetooth Low Energy (BLE) connectivity.

Users can test their firmware by launching the Unicleo-GUI application from within AlgoBuilder, to display outputs from running firmware. Unicleo-GUI is a dedicated sensor graphical user interface for use with ST’s sensor expansion software packages and X-NUCLEO boards, and lets users visualize sensor data as a time plot, scatter plot, or 3D plot.

AlgoBuilder is available now, and free to download from

STMicroelectronics |

PLL/VCO Solution Serves Next-Gen RF and Microwave Needs

Analog Devices has announced a synthesizer consisting of a phase-locked loop (PLL) with fully integrated voltage controlled oscillator (VCO) as well as integrated low dropout regulators (LDOs) and integrated tracking filter technology. The new ADF4371 supports RF/microwave system designs that must meet the most exacting next-generation requirements across multiple markets, including aerospace and defense, test/measurement, communications infrastructure, as well as high-speed converter clocking.

According to ADI, the ADF4371 is the highest frequency synthesizer on the market today and offers the widest continuous RF output range of 62 MHz to 32 GHz. Together with ultra-low PLL FOM (-234 dBc/Hz), ultra-low spurious (-100 dBc typ.), low VCO phase noise (-134 dBc/Hz at1 MHz offset at 8GHz), and with built-in tracking filter technology, this device leads the way for performance and adaptability. Its feature-rich, highly configurable architecture means that designers can now choose a single, ultra-compact, synthesizer solution to cover almost any LO/clock requirement within these frequency ranges, thereby reducing development costs, risk and time to market.

The ADF4371 facilitates implementation of high resolution (39-bit) fractional-N or integer-N PLL frequency synthesizers when used with an external loop filter and an external reference source. The wideband microwave VCO design allows frequencies from 62.5 MHz to 32 GHz to be generated. The device features the industry’s lowest jitter (36 fs at 10 GHz) and reference spurious (-100 dBc typ.), together with operation to 105°C without loss of lock.

For applications requiring very small compact footprints, the ADF4371 supports integrated power supply decoupling, integrated LDOs and integrated harmonic tracking filters. The tracking filter technology facilitates at least 30dB harmonic and sub-harmonic rejection across the entire VCO range. This hugely reduces the total solution footprint, particularly in the case where fixed range filters are required to meet these rejections across octave bandwidths. For applications that do not require the full frequency range capability of the ADF4371 (up to 32 GHz), ADI also offers the ADF4372 with operation up to 16 GHz.

The ADF4371 and ADF4372 are supported within ADI’s popular ADIsimPLL™ circuit design and evaluation tool that assists users in evaluating, designing and troubleshooting RF and microwave systems.

Analog Devices |

Silicon APDs are Optimized for LIDAR Applications

The Series 9 from First Sensor offers a wide range of silicon avalanche photodiodes (APDs) with very high sensitivity in the near infrared (NIR) wavelength range, especially at 905 nm. With their internal gain mechanism, large dynamic range and fast rise time the APDs are ideal for LIDAR systems for optical distance measurement and object recognition according to the time of flight method. Application examples include driver assistance systems, drones, safety laser scanners, 3D-mapping and robotics.

The Series 9 offers detectors as single elements as well as linear and matrix arrays with multiple sensing elements. The package options include rugged TO housings or flat ceramic SMD packages. The slow increase of the gain of the Series 9 photodiodes with the applied reverse bias voltage allows for easy and precise adjustments of high gain factors. For particularly low light levels, hybrid solutions are also available that further enhance the APD signal with an internal transimpedance amplifier (TIA). The integrated amplifier is optimally matched to the photodiode and allows compact setups as well as very large signal-to-noise ratios.

Using its own semiconductor manufacturing facility and extensive development capabilities, First Sensor can adapt its silicon avalanche photodiodes to specific customer requirements, such as sensitivity, gain, rise time or design.

Important features of the Series 9 APDs:

  • Very high sensitivity at 905 nm
  • Large dynamic range and fast rise time
  • Single element photodiodes as well as linear and matrix arrays
  • Rugged TO housings or flat ceramic SMD packages
  • Hybrid solutions with integrated TIA

First Sensor |

Tuesday’s Newsletter: IoT Tech Focus

Coming to your inbox tomorrow: Circuit Cellar’s IoT Technology Focus newsletter. Tomorrow’s newsletter covers what’s happening with Internet-of-Things (IoT) technology–-from devices to gateway networks to cloud architectures. This newsletter tackles news and trends about the products and technologies needed to build IoT implementations and devices.

Bonus: We’ve added Drawings for Free Stuff to our weekly newsletters. Make sure you’ve subscribed to the newsletter so you can participate.

Already a Circuit Cellar Newsletter subscriber? Great!
You’ll get your IoT Technology Focus newsletter issue tomorrow.

Not a Circuit Cellar Newsletter subscriber?
Don’t be left out! Sign up now:

Our weekly Circuit Cellar Newsletter will switch its theme each week, so look for these in upcoming weeks:

Embedded Boards.(6/26) The focus here is on both standard and non-standard embedded computer boards that ease prototyping efforts and let you smoothly scale up to production volumes.

Analog & Power. (7/3) This newsletter content zeros in on the latest developments in analog and power technologies including DC-DC converters, AD-DC converters, power supplies, op amps, batteries and more.

Microcontroller Watch (7/10) This newsletter keeps you up-to-date on latest microcontroller news. In this section, we examine the microcontrollers along with their associated tools and support products.

July (issue #336) Circuit Cellar Article Materials

Click here for the Circuit Cellar article code archive

p. 6: Op Amp Design Techniques: Analog Adventures, By Stuart Ball

Analog Devices |

p. 12: MCU-Based Motor Condition Monitoring: Sensors and Signals, By Amit Ashara

Texas Instruments |

p. 18: Wire Wrapping Revisited: For Prototypes and Projects, By Wolfgang Matthes

[1]   Matthes, Wolfgang: Microcontroller Modules for the Ambitious. Circuit Cellar, Issue 312, July 2016, S. 24-33.
[2]   Solderless Wrapping Manual. Doc-No. 130031371A. Honeywell Computer Control Division, November 1967.
[3]   Design Parameters for Wire-Wrap. Gardner-Denver Company, 1962.
[4]   Kilgrease, D. L.: Mechanization of Engineering Design Data. IBM, 1962.
[5]   Winters, Ryan: Wire wrapping vs. soldering: How and When to Use Wire Wrapping.
[6]   Xcelite Catalog. Apex Tool Group, LLC, 2014.
[7]   Tools for Telecom, Datacom, Electrical, and Electronics. JDV Products, Inc., 2018.[8]   Jonard Tools Catalogue No. 114. Jonard Tools, 2018.
[9]   Hookup Wire Catalog. Lit. No. HUW-Bro-1501. Alpha Wire, 2015.
[10] Wire-Wrap-Draht. Rollenware und konfektioniert. Catalog sheet (German).
[11] BPS BusBoard Prototype Systems 2016 Fall Product Catalog Rev 1610. BPS BusBoard Prototype Systems Ltd., 2016.
[12] Prototyping Products and accessories for the Eurocard/19″ Technology Market. Vero Catalogue 05.1. Vero Technologies Limited, 2005.
[13] Uncommitted and Microbus backplanes are an effective interconnect technology for general purpose small systems (16 05 Backplane white paper V2 25 May 16.).  Vero Technologies Limited, 2016.

Extra Information:

The author’s project homepage:

Historical documents ([2] to [4)]:

Tools ([6] to [8]):

Wire ([9]):

Pre-cut and pre-stripped wire [10]:

Prototyping Boards ([11] to [13]):

Alpha Wire |
BusBoard Prototype Systems |
Seltronics |
Vero Technologies |

Scroll down to the end of this web page to see the ADDENDUM  where we’ve posted several extra photos. These are photos that we were unable to fit into the print issue of Wolfgang Matthes’ article.

p. 26: MPEG-H Audio Brings New Dimensions to TV Sound, By Stefan Meltzer

Information on the MPEG-H Audio System is available at

Fraunhofer IIS |
upHear |

p. 30: EMC Analysis During PCB Layout: Catch Issues Earlier, By Craig Armenti

Mentor, A Siemens Business |

p. 34: Wireless Standards and Solutions for IoT: Protocol Choices Abound, By Jeff Child

Cypress Semiconductor |
Nordic Semiconductor |
NXP Semiconductor |
STMicrolectronics |
Texas Instruments |

p. 40: IoT Drives Extreme Low-Power Demands: Enabling “Always On”, By Jeff Child

Eta Compute |
Imprint Energy |
Nikola Labs |
Semtech |
Wiliot |

p. 44: IoT Interface Modules: Ready to Connect, By Jeff Child

Device Solutions |
Digi |
Espressif |
InnoComm Mobile Technology |
Jorjin Technologies |
NXP Semiconductor |
Rigado |
Telit |
U-blox |

p. 48: EMBEDDED SYSTEM ESSENTIALS: Verifying Code Readout Protection Claims: Think Like an Attacker, By Colin O’Flynn

ST Microelectronics. “STM32F303xB/C/D/E Reference Manual RM0316”.

ST Microelectronics. “USART protocol used in the STM32 bootloader. Application Note AN3155”.

Chris Gerlinsky. “Breaking Code Read Protection on the NXP LPC-family Microcontrollers”. RECON Brussels 2017.

Johannes Obermaier and Stefan Tatschner. “Shedding too much Light on a Microcontroller’s Firmware Protection”. WOOT ’17.

NXP Semiconductors |
STMicroelectronics |

p. 54: ABOVE THE GROUND PLANE: BLDC Fan Current: Motors and Measurements, By Ed Nisley

Background Circuit Cellar columns:

  • 2014-11 Universal Motor Control vs. Transistor SOA
  • 2015-01 Brute-force Motor Control
  • 2018-03 Stepper Motor Waveforms

Background blog posts:


p. 60: THE CONSUMMATE ENGINEER: Thermoelectric Cooling (Part 1): Failure Analysis, By George Novacek

[1] Peltier module TEC12706 Specification
[2]  Circuit Cellar 310, May 2016, George Novacek “Electronics Cooling”
[3] Adafruit Peltier Module Assembly
[4] Peltier Application Note
[5] Texas Instruments: Closed Loop Temperature Regulation

Adafruit |
Maxim Integrated |
Peltier Modules |
Texas Instruments |

p. 64: FROM THE BENCH: Electronic Speed Control (Part 1): Motor Evolution,
By Jeff Bachiochi

Figure 1 and Figure 2:

Figure 3:

PIC12F1822: 8-pin Flash Microcontroller : Microchip Technology

ESC-30A: 30A Brushless Motor Speed Controller RC BEC ESC:
Various brands available

2408 Brushless Outrunner Motor: Various brands available

Microchip Technology |
Propwashed |
Renesas Electronics |

ADDENDUM:  Provided here are several photos that we were unable to fit into the print version of “Wire Wrapping Revisited” by Wolfgang Matthes

More modules examples (similar to Figure 1):

Relay and power modules to be stacked onto a microcontroller module. Obviously, such a module must be located at the top. Therefore, it is no call to provide additional stackable connectors.


Stackable modules with housings that match. It looks fine. However, one can only use the respective module. Multi-module configurations are obviously not supported.

The small application system to the left consists of a microcontroller board and an LCD module. Obviously, it is not that easy to add further modules. But what to do if the two buttons are not enough? Here, a keypad and a connector for a PS/2 keyboard are shown. However, the parts have to be connected by jumper wires. They must be deposited loosely on the table or held in the hand because the boards do not even have mounting holes.


More application examples (similar to Figure 4 and Figure 5:

Experimenting with LEDs and relays.

LED-array modules can be inserted horizontally or vertically (the latter, for example, to demonstrate bar graph displays).


Class-D Audio Amplifiers Target the Smart Home

Texas Instruments (TI) has introduced three new digital-input Class-D audio amplifiers that enable engineers to deliver high-resolution audio in more smart-home and voice-enabled applications. By combining first-of-its-kind integration, real-time protection and new modulation schemes, TI’s new audio devices allow designers to reduce board space and overall bill of material (BOM) cost. These new amplifiers are designed for personal electronics applications with any power level, including smart speakers, sound bars, TVs, notebooks, projectors and Internet-of-Things (IoT) applications.

TAS2770 15-W audio amplifier: Claimed by TI to be the first wide-supply I/V sense amplifier, the TAS2770 (shown) offers state-of-the art, real-time speaker protection when paired with TI Smart Amp algorithms. The amplifier monitors loudspeaker behavior and increases loudness while improving audio quality in applications requiring small speakers. The TAS2770 is an audio front end (AFE) that combines a digital microphone input with a powerful I/V sense amplifier. The device captures voice and ambient acoustic information for echo cancellation or noise reduction in voice-enabled applications. The TAS2770 monitors battery voltage and automatically decreases gain when audio signals exceed a set threshold, helping designers avoid clipping and extend playback time through end-of-charge battery conditions without degrading sound quality.

TAS5825M audio amplifier: Designers can achieve high-resolution audio with minimal engineering effort due to the device’s 192-kHz input sampling frequency and flexible, integrated processing flows. Additionally, the TAS5825M provides bass enhancement and thermal protection for the speaker. The TAS5825M’s dedicated serial audio interface data output provides ambient sound information to the applications processor. Engineers can reduce idle-power losses and thermal dissipation without degrading sound quality with the TAS5825M’s proprietary hybrid-mode modulation scheme.

TAS3251 audio amplifier: TI says the TAS3251 is the first integrated digital-input solution to support the highest output power and performance at 2x 175 W, all in one single package. You can enable up to 96-kHz flexible processing and self-protection features including cycle-by-cycle current limit and DC speaker protection with the TAS3251.

Designers can use TI’s PurePath Console software to easily configure the TAS2770, TAS5825M and TAS3251 Class-D audio amplifiers. Engineers can jump-start their design with the TAS2770 Stereo Audio Subsystem Reference Design. Additional resources and reference designs are available to help engineers with their smart speaker designs.

The TAS2770 Class-D audio amplifier is now available in volume quantities through the TI store and authorized distributors. Additionally, preproduction samples of the TAS5825M are now available through the TI store. The TAS3251EVM evaluation module is available today through the TI store and authorized distributors, and production quantities of the TAS3251 amplifier will be available in 2Q 2018.

Texas Instruments |

July Circuit Cellar: Sneak Preview

The July issue of Circuit Cellar magazine is coming soon. And we’ve rustled up a great herd of embedded electronics articles for you to enjoy.

Not a Circuit Cellar subscriber?  Don’t be left out! Sign up today:


Here’s a sneak preview of July 2018 Circuit Cellar:


Wireless Standards and Solutions for IoT  
One of the critical enabling technologies making the Internet-of-Things possible is the set of well-established wireless standards that allow movement of data to and from low-power edge devices. Here, Circuit Cellar’s Editor-in-Chief, Jeff Child, looks at key wireless standards and solutions playing a role in IoT.

Product Focus: IoT Device Modules
The rapidly growing IoT phenomenon is driving demand for highly integrated modules designed to interface with IoT devices. This Product Focus section updates readers on this technology trend and provides a product album of representative IoT interface modules.


EMC Analysis During PCB Layout
If your electronic product design fails EMC compliance testing for its target market, that product can’t be sold. That’s why EMC analysis is such an important step. In his article, Mentor Graphics’ Craig Armenti shows how implementing EMC analysis during the design phase provides an opportunity to avoid failing EMC compliance testing after fabrication.

Extreme Low-Power Design
Wearable consumer devices, IoT sensors and handheld systems are just a few of the applications that strive for extreme low-power consumption. Beyond just battery-driven designs, today’s system developers want no-battery solutions and even energy harvesting. Circuit Cellar’s Editor-in-Chief, Jeff Child, dives into the latest technology trends and product developments in extreme low power.

Op Amp Design Techniques
Op amps can play useful roles in circuit designs linking the real analog world to microcontrollers. Stuart Ball shares techniques for using op amps and related devices like comparators to optimize your designs and improve precision.

Wire Wrapping Revisited
Wire wrapping may seem old fashioned, but this tried and true technology can solve some tricky problems that arise when you try to interconnect different kinds of modules like Arduino, Raspberry Pi and so on. Wolfgang Matthes steps through how to best employ wire wrapping for this purpose and provides application examples.


BLDC Fan Current
Today’s small fans and blowers depend on brushless DC (BLDC) motor technology for their operation. In this article, Ed Nisley explains how these seemingly simple devices are actually quite complex when you measure them in action. He makes some measurements on the motor inside a tangential blower and explores how the data relates to the basic physics of moving air.

Electronic Speed Control (Part 1)
An Electronic Speed Controller (ESC) is an important device in motor control designs, especially in the world of radio-controlled (RC) model vehicles. In Part 1, Jeff Bachiochi lays the groundwork by discussing the evolution of brushed motors to brushless motors. He then explores in detail the role ESC devices play in RC vehicle motors.

MCU-Based Motor Condition Monitoring
Thanks to advances in microcontrollers and sensors, it’s now possible to electronically monitor aspects of a motor’s condition, like current consumption, pressure and vibration. In this article, Texas Instrument’s Amit Ashara steps through how to best use the resources on an MCU to preform condition monitoring on motors. He looks at the signal chain, connectivity issues and A-D conversion.


Verifying Code Readout Protection Claims
How do you verify the security of microcontrollers? MCU manufacturers often make big claims, but sometimes it is in your best interest to verify them yourself. In this article, Colin O’Flynn discusses a few threats against code readout and looks at verifying some of those claimed levels.

Thermoelectric Cooling (Part 1)
When his thermoelectric water color died prematurely, George Novacek was curious whether it was a defective unit or a design problem. With that in mind, he decided to create a test chamber using some electronics combined with components salvaged from the water cooler. His tests provide some interesting insights into thermoelectric cooling.


Designing a Debug and Test Tool

While developing mixed signal IC products, I often longed for a personal, simple to use, analog and digital pattern generator tool. So after retiring, I decided to create one. Read how Validator 1, a USB benchtop debug and test tool, was developed.


by William Holt, retired founder of Holt IC

During a career largely spent developing mixed signal IC products, I often longed for a personal, simple to use, analog and digital pattern generator tool. Numerous occasions arose where it was necessary to check performance or parameters of an IC, a breadboard, or an application board. Sometimes the setup was trivial: a few supplies and a signal generator or two. And sometimes the setup was quite complex.  I had a few tools for the tougher problems but there was usually something not quite matching up – logic or interface voltages, offset, synchronization, limited pattern width or length, and limited pattern control options. After retiring, I looked for a project to fill the void and decided to take on the challenge of creating a personal debug and test tool.

The first step was to make a wish list for performance and functions:

  • 16 digital input / output (DIO) pins and 2 high voltage DACs
  • Able to interface with any digital voltage standard
  • run digital patterns from DC to 50 Mhz
  • have a pattern depth of at least 4 K per pin and up to 1,000 clocks at each pattern line
  • pattern controls for looping and branching
  • easily expandable to synchronously drive up to 64 channels in parallel
  • test any channel for its digital state at any time step and show where the fault is in the pattern
  • output arbitrary analog waveforms in the -10V to +10V range in sync with the digital
  • start patterns from either an edge or a button push
  • nonvolatile memory for standalone operation
  • easy to program
  • under $500

But first, why should I try to create such a tool if one is already available? There are indeed options to consider. Let’s take a closer look at some possibilities:

Off the Shelf Pattern Generators

A variety of commercial products could fulfill the digital pattern generator function and some include analog capability. However the “under $500” criteria eliminates most. The remaining options usually require converting the pattern to code if the pattern is large and complex. Some do provide software to input patterns via a timing diagram. Timing diagrams work fine for simple requirements.

Microcontrollers with GPIO and DACs

This option can work provided the output/input voltages available at the digital and analog pins are compatible with the DUT.  Manufacturers provide development boards and software that allow access to the GPIO pins and other peripheral assets. The issues are:

1. Getting significant pattern depth (memory) behind each pin
2. Finding an easy way to translate pattern into code.


FPGAs can provide adequate memory bits behind each pin and a variety of on-chip resources.  If you are willing to spend the time to design the tool yourself, this path will work. Indeed, this became my solution. I embarked on a software / hardware design project to make a unique product called Validator 1

The Validator Pattern Generator Design

The hardware implementation of a digital and analog bit pattern generator is straightforward. Consider the architecture shown in the Block Diagram below. The basic output mechanism is to clock the memory address counter, read the next line of massively parallel memory bits, and feed the result to the outside world. The faster this path, the higher the maximum frequency. The data accessed with each read cycle is a line of pattern data.  Lines of pattern then correspond to a memory address.

Before a pattern can be run, we need a convenient way to load memory with the pattern. The method selected was by USB communication with a host program.


USB Interface

Setup and pattern data will be read from a CSV file and passed by host software, via USB, to pattern memory RAM and, simultaneously, to duplicate nonvolatile pattern memory RAM. The ideal design would combine both RAMs into one memory but issues with speed and available FPGA resources prohibit this option for now.

The 8051 microcontroller provides the USB interface. A host command initiates an 8051 sequence to convert the serial USB stream into 8 bit bytes which are transferred to the Memory Write State Machine by GPIO.   Additional GPIO pins signal start, finish, and byte order. The first bytes pass a code telling the State Machine whether this will be a memory load or alternatively, a command for the Pattern Control block, like Run or Reset.

The Auto Load Sequencer block provides the mechanism to read back nonvolatile memory into pattern memory when initiated by a Load button closure. This fulfills the goal of standalone operation. Data flow to the State Machine from nonvolatile memory is identical to a USB download from the 8051.

The Periodic Status Transmit block creates a serial UART string at set intervals and sends it to the 8051.   This string is coded to display the status, address, and fail channels on the host program control panel. The 8051 automatically passes it by USB to the host.

Setup Memory block

Each pattern load starts with a string of Setup Data for these setup choices:

Select External or Internal Clock
Select Clock division from 1 to 1024 (0 equals divide by 1,000,000)
Select whether to start on a SYNC input edge or on the Run button closure
Select which SYNC edge, positive or negative
Select whether to stop the pattern immediately on any Fail condition
Select whether to output the internal clock at the EXT CLK input (provide a clock source for parallel units)

Jump Address Memory block

The pattern memory address counter can be jammed with a Jump address. The CSV file has a label column which, if not void, will trigger a write of the current Line address into one of 15 bytes of Jump address memory. When a subsequent line command requires a jump, the label specified is the address of the Jump address. The Jump can be qualified by the result of a test at the current line.

Pattern Control and Timing block

What is seen at the DIO and DAC pins as a pattern executes is under the control of the Pattern Memory Address Counter.   Clocking or jamming the counter always causes a Read cycle.  So controlling when to clock or jam the counter controls the pattern. The Control Block does this task. It reads Line commands and the number of clocks to issue. It also controls start and stop and reports run status to the host.

DIO State Decoder and Test block

DIO data is not just force 1 or 0. To test and to interface to 3 state busses, the pins need further options:

Drive a One
Drive a Zero
High impedance
Test to be a One
Test to be a Zero
Output the System Clock


The entire design, excepting the DACs and nonvolatile memory, fits an FPGA, the Lattice MachX02 7000.  The design includes several housekeeping details such as :

  1. For parallel units running in synchronous operation, the FPGA provides two pins, a Start input and a Start output. One unit is chosen the master and its Start output would be wired to all slave Start inputs.
  2. Pause and then step or run again.
  3. Backup the control panel display with LEDs for standalone status display.
  4. Provide outputs that pulse the moment a test fails.

Mechanical Design

A Toolless plastic design was chosen for the enclosure which mates to a single PCB.

The final Validator hardware

The next step was to figure out the best way to get pattern data into a CSV file.


A pattern generator tool might sit in the toolbox for long periods until setup stimuli are needed. If specialized software is required to program the pattern, a refresher study of the manuals might have to proceed preparing patterns. Might there be an advantage if the pattern creation method used familiar software?

Since its inception, spreadsheet software has been adopted for a variety of chores, both business and personal. It could fit the label of “familiar software” and has advantages for creating patterns. The format could look like traditional ATE (Automated Test Equipment) with line by line time steps. Strong editing capabilities and auto indexing could make large patterns manageable. With an elapsed time column it would be possible to write equations as a function of time for the DAC voltages. For frequently used communication protocols, a couple of worksheets could make data handling simple, one for inputting data for transactions and another to automatically read the data and distribute to the right places for the download file. Choosing a fixed spreadsheet template should make it possible to enter pattern data immediately without refresher issues. A spreadsheet is easily saved as a CSV file.

Once settled on using the spreadsheet to input patterns, the next step was to assign the order of data in a template. The selected presentation was arbitrary and hopefully flows in a logical sequence.

FIGURE 2.  Pattern Entry Template

When the host software reads the CSV file, it will ignore any line without a Line Number in column A with the exception of Setup Data in row 7. It also ignores any data after the last column, which is column H for Setup Data and column X for Line Data. The ignored columns and rows can be used for annotation or housekeeping.


With hardware and pattern entry template defined, a host program is required to read the CSV file, format and deliver data to the USB sequencer, and receive back USB data to display status and results.

Visual C++ MFC was selected for this task.   A simple control panel with buttons and edit boxes was constructed using a Dialog Application:

                                        MFC Dialog Panel

Host software design tasks included:

  • Recognize and administrate the USB connection
  • Provide browsing for a CSV file to download
  • Error check the CSV file and provide intuitive messages to assist user debugging.
  • Send data from the selected download file to hardware by USB
  • Send codes to hardware when control button controls are pushed.
  • Periodically check for USB data coming from hardware and update the display in the edit boxes.


The DIO channels from the FPGA are 3.3V. To satisfy the “any digital voltage” objective, translators are required. A Breakout Board accessory is also needed to provide a connector option for interfacing DIO channels to a DUT. It was decided to combine the two requirements and design a Breakout Board with translators.

Each translated DIO channel should be bidirectional just like the non-translated FPGA DIO pins. One way to accomplish this is to use two 3.3V channels to make one translated channel. One 3.3V DIO channel is data (one, zero, or input) and the other 3.3V channel supplies direction. A TI SN74LVC1T45 bus transceiver was selected for the translators.

For translated patterns, a worksheet was made to look like the 16 channel template except there are only 8 DIO channels. The data from this worksheet is read by the cells of a standard 16 DIO template in a separate worksheet. The “reading” worksheet will become the CSV file. The “reading” DIO cells interpret the 8 translation DIO channel inputs to automatically create 8 pairs, direction and data. The user only has to remember to save the “reading” worksheet to CSV format for download.

The Breakout Board has duplicate connectors on each side of the board. One set is input to the translators. The other set is near the uncommitted area for wiring a mating connector to the DUT or perhaps to add interface electronics like protocol bus transceivers.

                                                        Breakout Board with Translators



To illustrate applying the Validator to a real world task, I wrote a step by step Example Application note, “Measure an ARINC 429 Receiver Threshold”. The DACs were used to generate a ramping amplitude differential voltage and the digital was used to do SPI communication. The target is a mixed signal IC, the HI-3598 which has an analog receiver whose threshold is measured.

Example Application Setup

 SPI routines followed by differential DAC waveforms


The finished product is available for purchase by a newly formed business called Sequim Tek located in, of course, Sequim, Washington.

Example Patterns are available for download including a pulse generator, a waveform generator, and an SPI communication example. They are meant to illustrate a few of the ways a pattern created by a spreadsheet can be customized.

About the Author
William Holt started designing CMOS ICs at Motorola SPD in 1970 after receiving a BSEE from the University of Utah. In 1976, he founded Holt IC in Southern California which provides standard IC products to the avionics and military markets.

Sponsored by: Sequim Tek