Fancy Filtering with the Teensy 3.6

Arm-ed for DSP

Signal filtering entails some tricky tradeoffs. A fast MCU that provides hardware-based floating-point capability eases some of those trade-offs. Here, Brian has used the Arm-based Teensy MCU modules to serve those needs. Here, Brian taps the Teensy 3.6 Arm MCU module to perform real-time audio FFT-convolution filtering.

By Brian Millier

Signal filtering can be done either with analog circuitry or digitally using a microcontroller (MCU) coupled with analog-to-digital and digital-to-analog converters. The strength of analog filters is that they can cover wide frequency ranges. If they are designed entirely with passive components, the range of signal amplitudes that can be handled is limited only by the voltage rating of the various capacitors that are used. Additionally, they don’t add much, if any, noise to the signal. However, a limitation of analog filters is that they can’t provide a sharp cut-off rate at their corner frequency (Fc), unless you cascade many filter sections and use close-tolerance components.

If you need high-performance filters, then digital filters might be the way to go. You can design very sharp low-pass, high-pass, notch and band-pass filters using digital techniques, if you use high-resolution ADC/DACs to convert the analog signal into the digital domain and (optionally) back to the analog domain. However, the MCU that you use must be fast and, in general, feature hardware-based floating-point operations. Two years ago, I discovered a line of Arm-based MCU modules that fill the bill nicely.

In Circuit Cellar issues 324 (July 2017) and 325 (August 2017), I described a digital guitar amplifier based upon the Teensy 3.2 Module, which contains an Arm Cortex-M4 MCU. The analog guitar signal was converted to a 16-bit digital signal for processing, and then back to an analog signal for power amplification, by an NXP Semiconductor SGTL5000 Codec contained on the PJRC Audio Shield. This project was made possible largely due to the extremely powerful Audio library provided by the manufacturer of the Teensy modules. This library consists of many audio functions, all of which operate using DMA transfers and interrupt service routines (that is, as a background task). The sampling is done at CD quality (44,100 samples/s at 16-bit resolution).

That project involved many different audio functions—some from the Teensy Audio Library, and some that I wrote myself. The filtering I used for the project was in the form of a 5-band parametric equalizer (EQ). This consists of five blocks of band-pass filters, each one centered on a specific frequency in the audible range. Such an EQ is basically a sophisticated “tone control” for the guitar signal. While most of the other guitar signal processing was done within the Teensy 3.2 MCU, using the Audio library, the 5-band parametric EQ was handled by a DSP block contained within the SGTL5000 Codec on the Teensy Audio Shield.

After finishing that project, I became interested in more sophisticated filtering algorithms that could be performed by the Arm MCU found on the Teensy modules. The Teensy Audio Library routines work with all the Arm-based MCUs in the Teensy module family (except the lowest-cost LC model). The Audio library contains three types of digital filters:

1) Biquad (low pass, high pass, band pass, notch)
2) FIR (up to 200 taps)
3) State-variable (Chamberlin)

The Biquad algorithm executes quickly, and its coefficients are easy to calculate on the fly, which makes it easy to change the filter bandwidth and Fc quickly. Finite impulse response (FIR) filters can provide much better filter characteristics, if you configure them with enough “taps”. However, as you increase the number of taps used, the execution time increases proportionately.

All the above filters use 16-bit, fixed-point math (Arm Cortex M4 DSP instructions using the Q15 data format). This is fast and reasonably accurate, but not enough to provide very sharp filter “skirts”. When you attempt to cascade several sections of such filters, you start to see the limitations in the precision of the fixed-point math.

The higher-end Teensy modules (Teensy 3.5 and 3.6) contain the more powerful Arm Cortex M4F core. These devices have hardware floating-point instructions, which basically allow you to do floating-point operations as quickly as you could do the 16-bit fixed-point operations with the DSP instructions available on Teensy 3.2’s Arm Cortex M4 MCU.

Figure 1
Top view of the Teensy 3.6 Arm MCU module. To the right is the on-board MicroSD socket, which accepts the MicroSD card containing the Cabinet Impulse Response file.

By using a Teensy 3.6 with hardware floating-point instructions, I figured that I could handle more sophisticated filtering algorithms. Another consideration was that the Teensy 3.6 MCU runs at 180 MHz, compared to the 72 MHz clock speed of the Teensy 3.2. Also, the Teensy 3.6 can be safely over-clocked at 240 MHz, compared to the 120 MHz maximum overclocked speed of the Teensy 3.2. Figure 1 shows the Teensy 3.6 module. Figure 2 shows the Audio Shield that I used. It contains the NXP SGTL5000 Codec device (A/D and D/A converters, mic preamplification, headphone driver and digital signal processing).

Figure 2
Top view of the Teensy Audio Shield. The two rows of 14 holes are fitted with header pins that plug directly into the Teensy 3.6 MCU module. All interconnections between the two boards are via these 28 pins.

CONVOLUTION FILTERING

Although I have used digital filters in FIR and Biquad configurations, prior to this project I wasn’t familiar with the term “convolution” filtering. As part of my music/recording hobby, I had encountered the term convolution regarding:

1) Guitar amplifier cabinet simulation
2) High-end, “space-accurate” reverberation processors

Convolution reverberation processors are not relevant to this discussion. However, guitar amplifier cabinet simulation is basically a fancy way of saying that you are simulating the exact frequency/phase response of a guitar amplifier and its loudspeaker(s), mounted in a specific cabinet, with the recording microphone oriented a specific way.

The “shape” of the frequency response curve of any given guitar amplifier/speaker combination will not be a “flat” response over the useful range of guitar notes. Instead it will consist of many small peaks and dips over the frequency range of interest. These “aberrations” provide the distinctive sound of interest to the musician. To some extent, one can simulate a given guitar amplifier/speaker by using a multiband parametric equalizer (EQ) and fiddling with it until it sounds the way you know the actual amplifier/speaker sounds. However, experts in the field learned that they could go one step further using the following method.

Rather than feeding an actual guitar signal into the amplifier/speaker cabinet, they feed it a short pulse, with rise/fall times as fast as possible. This short pulse is called a “finite-impulse signal.” The sound emitted by the speaker cabinet is then picked up by a professional-quality microphone, amplified, converted to digital form and stored in a file. This file represents the FIR of the guitar amplifier/speaker cabinet. I admit that I don’t have the best understanding of the mathematical “magic” involved here, but suffice it to say that all the frequency response “personality” of the guitar amplifier/speaker cabinet is contained in the finite-impulse-response (FIR) file that has been collected. The higher the sample rate used to record the impulse, the better the simulation, and the larger this FIR file will be.

Once you have this FIR file, you can use it to provide the coefficients needed for a digital FIR filter. If you pass your “raw” guitar signal through this FIR filter, it will be modified in virtually the same way that it would be if it were sent out to the specifically modeled guitar amplifier/speaker cabinet. Effectively, you can digitally record a “raw” guitar signal, which, when converted back to analog and listened to, will sound as if you were listening to it “live,” through the specific guitar amplifier/speaker that you have modeled. The FIR filter routine does what’s called a “convolution” of the guitar’s time-domain signal with the FIR array of coefficients—which is also time-domain data.

FOCUSING ON FIR

Once you absorb the idea behind this simulation technique, it becomes clear that you could implement a complex digital filter to reproduce almost any complex frequency response with this technique. I’m certain that mathematicians and electronics engineers in the communication field discovered and used this technique to design complex filters long before guitar players saw its usefulness. However, it was the guitar cabinet simulation concept that led me to investigate the FIR filtering technique more fully..  …

Read the full article in the May 346 issue of Circuit Cellar
(Full article word count: 6284 words; Figure count: 8 Figures.)

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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.

February Circuit Cellar: Sneak Preview

The February issue of Circuit Cellar magazine is coming soon. We’ve raised up a bumper crop of in-depth embedded electronics articles just for you, and packed ’em into our 84-page magazine.

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MCUs ARE EVERYWHERE, DOING EVERYTHING

Electronics for Automotive Infotainment
As automotive dashboard displays get more sophisticated, information and entertainment are merging into so-called infotainment systems. That’s driving a need for powerful MCU- and MPU-based solutions that support the connectivity, computing and interfacing needs particular to these system designs. In this article, Circuit Cellar’s Editor-in-Chief, Jeff Child, looks at the technology and trends feuling automotive infotainment.

Inductive Sensing with PSoC MCUs
Inductive sensing is shaping up to be the next big thing for touch technology. It’s suited for applications involving metal-over-touch situations in automotive, industrial and other similar systems. In his article, Nishant Mittal explores the science and technology of inductive sensing. He then describes a complete system design, along with firmware, for an inductive sensing solution based on Cypress Semiconductor’s PSoC microcontroller.

Build a Self-Correcting LED Clock
In North America, most radio-controlled clocks use WWVB’s transmissions to set the correct time. WWVB is a Colorado-based time signal radio station near. Learn how Cornell graduates Eldar Slobodyan and Jason Ben Nathan designed and built a prototype of a Digital WWVB Clock. The project’s main components include a Microchip PIC32 MCU, an external oscillator and a display.

WE’VE GOT THE POWER

Product Focus: ADCs and DACs
Analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) are two of the key IC components that enable digital systems to interact with the real world. Makers of analog ICs are constantly evolving their DAC and ADC chips pushing the barriers of resolution and speeds. This new Product Focus section updates readers on this technology and provides a product album of representative ADC and DAC products.

Building a Generator Control System
Three phase electrical power is a critical technology for heavy machinery. Learn how US Coast Guard Academy students Kent Altobelli and Caleb Stewart built a physical generator set model capable of producing three phase electricity. The article steps through the power sensors, master controller and DC-DC conversion design choices they faced with this project.

EMBEDDED COMPUTING FOR YOUR SYSTEM DESIGN

Non-Standard Single Board Computers
Although standard-form factor embedded computers provide a lot of value, many applications demand that form take priority over function. That’s where non-standard boards shine. The majority of non-standard boards tend to be extremely compact, and well suited for size-constrained system designs. Circuit Cellar Chief Editor Jeff Child explores the latest technology trends and product developments in non-standard SBCs.

Thermal Management in machine learning
Artificial intelligence and machine learning continue to move toward center stage. But the powerful processing they require is tied to high power dissipation that results in a lot of heat to manage. In his article, Tom Gregory from 6SigmaET explores the alternatives available today with a special look at cooling Google’s Tensor Processor Unit 3.0 (TPUv3) which was designed with machine learning in mind.

… AND MORE FROM OUR EXPERT COLUMNISTS

Bluetooth Mesh (Part 1)
Wireless mesh networks are being widely deployed in a wide variety of settings. In this article, Bob Japenga begins his series on Bluetooth mesh. He starts with defining what a mesh network is, then looks at two alternatives available to you as embedded systems designers.

Implementing Time Technology
Many embedded systems need to make use of synchronized time information. In this article, Jeff Bachiochi explores the history of time measurement and how it’s led to NTP and other modern technologies for coordinating universal date and time. Using Arduino and the Espressif System’s ESP32, Jeff then goes through the steps needed to enable your embedded system to request, retrieve and display the synchronized date and time to a display.

Infrared Sensors
Infrared sensing technology has broad application ranging from motion detection in security systems to proximity switches in consumer devices. In this article, George Novacek looks at the science, technology and circuitry of infrared sensors. He also discusses the various types of infrared sensing technologies and how to use them.

The Art of Voltage Probing
Using the right tool for the right job is a basic tenant of electronics engineering. In this article, Robert Lacoste explores one of the most common tools on an engineer’s bench: oscilloscope probes, and in particular the voltage measurement probe. He looks and the different types of voltage probes as well as the techniques to use them effectively and safely.

Highly Integrated, Precision ADCs and DACs Feature Small Footprint

Texas Instruments (TI) has introduced four tiny precision data converters. The new data converters enable designers to add more intelligence and functionality, while shrinking system board space. The DAC80508 and DAC70508 are eight-channel precision digital-to-analog converters (DACs) that provide true 16- and 14-bit resolution, respectively. The ADS122C04 and ADS122U04 are 24-bit precision analog-to-digital converters (ADCs) that feature a two-wire, I2C-compatible interface and a two-wire, UART-compatible interface, respectively. The devices are optimized for a variety of small-size, high-performance or cost-sensitive industrial, communications and personal electronics applications. Examples include optical modules, field transmitters, battery-powered systems, building automation and wearables.

Both DACs include a 2.5-V, 5-ppm/°C internal reference, eliminating the need for an external precision reference. Available in a 2.4-mm-by-2.4-mm die-size ball-grid array (DSBGA) package or wafer chip-scale package (WCSP) and a 3-mm-by-3-mm quad flat no-lead (QFN)-16 package, these devices are up to 36 percent smaller than the competition. The new DACs eliminate the typical trade-off between high performance and small size, enabling engineers to achieve the best system accuracy, while reducing board size or increasing channel density.

In addition to their compact size, the DAC80508 and DAC70508 provide true, 1 least significant bit (LSB) integral nonlinearity to achieve the highest level of accuracy at 16- and 14-bit resolution – up to 66 percent better linearity than the competition. They are fully specified over a -40°C to +125°C extended temperature range and provide features such as cyclic redundancy check (CRC) to increase system reliability.

The tiny, 24-bit precision ADCs are available in 3-mm-by-3-mm very thin QFN (WQFN)-16 and 5-mm-by-4.4-mm thin-shrink small-outline package (TSSOP)-16 options. The two-wire interface requires fewer digital isolation channels than a standard serial peripheral interface (SPI), reducing the overall cost of an isolated system. These precision ADCs eliminate the need for external circuitry by integrating a flexible input multiplexer, a low-noise programmable gain amplifier, two programmable excitation current sources, an oscillator and a precision temperature sensor.

Both ADC devices feature a low-drift 2.048-V, 5-ppm/°C internal reference. Their internal 2 percent accurate oscillators help designers improve power-line cycle noise rejection, enabling higher accuracy in noisy environments. With gains from 1 to 128 and noise as low as 100 nV, designers can measure both small-signal sensors and wide input ranges with one ADC. These device families, which also include pin-to-pin-compatible 16-bit options, give designers the flexibility to meet various system requirements by scaling performance up or down.

Engineers can evaluate the new data converters with the DAC80508 evaluation module, the ADS122C04 evaluation module and the ADS122U04 evaluation module, all available today for $99.00 from the TI store and authorized distributors.

TI’s new tiny DACs and ADCs are available now with pricing ranging from $3.95 to $9.99 (1,000s).

Texas Instruments | www.ti.com

July Circuit Cellar: Sneak Preview

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TECHNOLOGIES FOR THE INTERNET-OF-THINGS

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.

TOOLS AND TECHNIQUES AT THE DESIGN PHASE

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.

DEEP DIVES ON MOTOR CONTROL AND MONITORING

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.

AND MORE FROM OUR EXPERT COLUMNISTS

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.

 

June Circuit Cellar: Sneak Preview

The June issue of Circuit Cellar magazine is coming soon. And we’ve planted a lovely crop of embedded electronics articles for you to enjoy.

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PCB DESIGN AND POWER: MAKING SMART CHOICES

PCB Design and Verification
PCB design tools and methods continue to evolve as they race to keep pace with faster, highly integrated electronics. Automated, rules-based chip placement is getting more sophisticated and leveraging AI in interesting ways. And supply chains are linking tighter with PCB design processes. Circuit Cellar Chief Editor Jeff Child looks at the latest PCB design and verification tools and technologies.

PCB Ground Planes
Tricky design decisions crop up when you’re faced with crafting a printed circuit board (PCB) for any complex system—and many of them involve the ground plane. There is dealing with noisy components and deciding between a common ground plane or separate ones—and that’s just the tip of the iceberg. Robert Lacoste shares his insights on the topic, examining the physics, simulation tools and design examples of ground plane implementations.

Product Focus: AC-DC Converters
To their peril, embedded system developers often treat their choice of power supply as an afterthought. But choosing the right AC-DC converter is critical to the ensuring your system delivers power efficiently to all parts of your system. This Product Focus section updates readers on these trends and provides a product album of representative AC-DC converter products.

SENSORS TAKE MANY FORMS AND FUNCTIONS

Sensors and Measurement
While sensors have always played a key role in embedded systems, the exploding Internet of Things (IoT) phenomenon has pushed sensor technology to the forefront. Any IoT implementation depends on an array of sensors that relay input back to the cloud. Circuit Cellar Chief Editor Jeff Child dives into the latest technology trends and product developments in sensors and measurement.

Passive Infrared Sensors
One way to make sure that lights get turned off when you leave a room is to use Passive Infrared (PIR) sensors. Jeff Bachiochi examines the science and technology behind PIR sensors. He then details how to craft effective program code and control electronics to use PIR sensors is a useful way.

Gesture-Recognition in Boxing Glove
Learn how two Boston University graduate students built a gesture-detection wearable that acts as a building block for a larger fitness telemetry system. Using a Linux-based Gumstix Verdex, the wearable couples an inertial measurement unit with a pressure sensor embedded in a boxing glove to recognize the user’s hits and classify them according to predefined, user-recorded gestures.

SECURITY, RELIABILITY AND MORE

Internet of Things Security (Part 3)
In this next part of his article series on IoT security, Bob Japenga looks at the security features of a specific series of microprocessors: Microchip’s SAMA5D2. He examines these security features and discusses what protection they provide.

Aeronautical Communication Protocols
Unlike ground networks, where data throughout is the priority, avionics networks are all about reliability. As a result, the communications protocols used in for aircraft networking seem pretty obscure to the average engineer. In this article, George Novacek reviews some of the most common aircraft comms protocols including ARINC 429, ARINC 629 and MIL-STD-1553B

DEEP DIVES ON PROCESSOR DESIGN AND DIGITAL SIGNAL PROCESSING

Murphy’s Laws in the DSP World (Part 1)
A Pandora’s box of unexpected issues gets opened the moment you move from the real world of analog signals and enter the world of digital signal processing (DSP). In Part 1 of this new article series, Mike Smith defines six “Murphy’s Laws of DSP” and provides you with methods and techniques to navigate around them.

Processor Design Techniques and Optimizations
As electronics get smaller and more complex day by day, knowing the basic building blocks of processors is more important than ever. In this article, Nishant Mittal explores processor design from various perspectives—including architecture types, pipelining and ALU varieties.

April Circuit Cellar: Sneak Preview

The April issue of Circuit Cellar magazine is coming soon. And we’ve got a healthy serving of embedded electronics articles for you. Here’s a sneak peak.

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NAVIGATING THE INTERNET-OF-THINGS

IoT: From Gateway to Cloud
In this follow on to our March “IoT: Device to Gateway” feature, this time we look at technologies and solutions for the gateway to cloud side of IoT.  Circuit Cellar Chief Editor Jeff Child examines the tools and services available to get a cloud-connected IoT implementation up and running.

Texting and IoT Embedded Devices (Part 2)
In Part 1, Jeff Bachiochi laid the groundwork for describing a project involving texting. He puts that into action this, showing how to create messages on his Espressif System’s ESP8266EX-based device to be sent to an email account and end up with those messages going as texts to a cell phone.

Internet of Things Security (Part 2)
In this next part of his article series on IoT security, Bob Japenga takes a look at side-channel attacks. What are they? How much of a threat are they? And how can we prevent them?

Product Focus: 32-Bit Microcontrollers
As the workhorse of today’s embedded systems, 32-bit microcontrollers serve a wide variety of embedded applications—including the IoT. This Product Focus section updates readers on these trends and provides a product album of representative 32-bit MCU products.

GRAPHICS, VISION AND DISPLAYS

Graphics, Video and Displays
Thanks to advances in displays and innovations in graphics ICs, embedded systems can now routinely feature sophisticated graphical user interfaces. Circuit Cellar Chief Editor Jeff Child dives into the latest technology trends and product developments in graphics, video and displays.

Color Recognition and Segmentation in Real-time
Vision systems used to require big, multi-board systems—but not anymore. Learn how two Cornell undergraduates designed a hardware/software system that accelerates vision-based object recognition and tracking using an FPGA SoC. They made a min manufacturing line to demonstrate how their system can accurately track and categorize manufactured candies carried along a conveyor belt.

SPECIFICATIONS, QUALIFICATIONS AND MORE

Component tolerance
We perhaps take for granted sometimes that the tolerances of our electronic components fit the needs of our designs. In this article, Robert Lacoste takes a deep look into the subject of tolerances, using the simple resistor as an example. He goes through the math to help you better understand accuracy and drift along with other factors.

Understanding the Temperature Coefficient of Resistance
Temperature coefficient of resistance (TCR) is the calculation of a relative change of resistance per degree of temperature change. Even though it’s an important spec, different resistor manufacturers use different methods for defining TCR. In this article, Molly Bakewell Chamberlin examines TCR and its “best practice” interpretations using Vishay Precision Group’s vast experience in high-precision resistors.

Designing of Complex Systems
While some commercial software gets away without much qualification during development, the situation is very different when safety in involved. For aircraft, vehicles or any complex system where failure unacceptable, this means adhering to established standards throughout the development life cycle. In this article, George Novacek tackles these issues and examines some of these standards namely ARP4754.

AND MORE IN-DEPTH PROJECT ARTICLES

Build a Marginal Oscillator Proximity Switch
A damped or marginal oscillator will switch off when energy is siphoned from its resonant LC tank circuit. In his article, Dev Gualtieri presents a simple marginal oscillator that detects proximity to a small steel screw or steel plate. It lights an LED, and the LED can be part of an optically-isolated solid-state relay.

Obsolescence-Proof Your UI (Part 1)
After years of frustration dealing with graphical interface technologies that go obsolete, Steve Hendrix decided there must be a better way. Knowing that web browser technology is likely to be with us for a long while, he chose to build a web server that could perform common operations that he needed on the IEEE-488 bus. He then built it as a product available for sale to others—and it is basically obsolescence-proof.

 

 

March Circuit Cellar: Sneak Preview

The March issue of Circuit Cellar magazine is coming soon. And we’ve got a healthy serving of embedded electronics articles for you. Here’s a sneak peak.

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TECHNOLOGY FOR THE INTERNET-OF-THINGS

IoT: From Device to Gateway
The Internet of Things (IoT) is one of the most dynamic areas of embedded systems design today. This feature focuses on the technologies and products from edge IoT devices up to IoT gateways. Circuit Cellar Chief Editor Jeff Child examines the wireless technologies, sensors, edge devices and IoT gateway technologies at the center of this phenomenon.

Texting and IoT Embedded Devices
Texting has become a huge part of our daily lives. But can texting be leveraged for use in IoT Wi-Fi devices? Jeff Bachiochi lays the groundwork for describing a project that will involve texting. In this part, he gets into out the details for getting started with a look at Espressif System’s ESP8266EX SoC.

Exploring the ESP32’s Peripheral Blocks
What makes an embedded processor suitable as an IoT or home control device? Wi-Fi support is just part of the picture. Brian Millier has done some Wi-Fi projects using the ESP32, so here he shares his insights about the peripherals on the ESP32 and why they’re so powerful.

MICROCONTROLLERS HERE, THERE & EVERYWHERE

Designing a Home Cleaning Robot (Part 4)
In this final part of his four-part article series about building a home cleaning robot, Nishant Mittal discusses the firmware part of the system and gets into the system’s actual operation. The robot is based on Cypress Semiconductor’s PSoC microcontroller.

Apartment Entry System Uses PIC32
Learn how a Cornell undergraduate built a system that enables an apartment resident to enter when keys are lost or to grant access to a guest when there’s no one home. The system consists of a microphone connected to a Microchip PIC32 MCU that controls a push solenoid to actuate the unlock button.

Posture Corrector Leverages Bluetooth
Learn how these Cornell students built a posture corrector that helps remind you to sit up straight. Using vibration and visual cues, this wearable device is paired with a phone app and makes use of Bluetooth and Microchip PIC32 technology.

INTERACTING WITH THE ANALOG WORLD

Product Focus: ADCs and DACs
Makers of analog ICs are constantly evolving their DAC and ADC chips pushing the barriers of resolution and speeds. This new Product Focus section updates readers on this technology and provides a product album of representative ADC and DAC products.

Stepper Motor Waveforms
Using inexpensive microcontrollers, motor drivers, stepper motors and other hardware, columnist Ed Nisley built himself a Computer Numeric Control (CNC) machines. In this article Ed examines how the CNC’s stepper motors perform, then pushes one well beyond its normal limits.

Measuring Acceleration
Sensors are a fundamental part of what make smart machines smart. And accelerometers are one of the most important of these. In this article, George Novacek examines the principles behind accelerometers and how the technology works.

SOFTWARE TOOLS AND PROTOTYPING

Trace and Code Coverage Tools
Today it’s not uncommon for embedded devices to have millions of lines of software code. Trace and code coverage tools have kept pace with these demands making it easier for embedded developers to analyze, debug and verify complex embedded software. Circuit Cellar Chief Editor Jeff Child explores the latest technology trends and product developments in trace and code coverage tools.

Manual Pick-n-Place Assembly Helper
Prototyping embedded systems is an important part of the development cycle. In this article, Colin O’Flynn presents an open-source tool that helps you assemble prototype devices by making the placement process even easier.