About Circuit Cellar Staff

Circuit Cellar's editorial team comprises professional engineers, technical editors, and digital media specialists. You can reach the Editorial Department at editorial@circuitcellar.com, @circuitcellar, and facebook.com/circuitcellar

New RP6V2 Robot Kit

Global Specialties recently introduced a new RP6V2 Robot Kit with RC5 remote and battery charger. The C-programmable autonomous mobile robot system is accessible enough for students and electronics enthusiasts to use. It comes with several example programs and a large C function library.

Source: Global Specialties

Source: Global Specialties

Features:

  • Atmel ATmega32 8-bit RISC microcontroller with 8 MIPS and an 8-MHz clock
  • Delivered fully assembled (no soldering needed)
  • CD with software and 138-page manual
  • AVR-GCC and RobotLoader open-source software for use with Windows and Linux
  • Programmable in C
  • Receives IR codes in RC5 format from the included remote control
  • USB Interface for easy programming and communication
  • Modular I2C bus expansion system
  • Expansion boards may be stacked as needed
  • Sample C programs and large C function library
  • Powerful tank drive train can negotiate steep ramps and obstacles
  • Large payload capacity
  • Light, collision, speed and IR-obstacle sensors integrated
  • Two 7.2-V DC motors
  • 625 CPR encoder resolution for precise speed regulation
  • Six PCB expansion areas

Source: Global Specialties

 

 

SmartFusion2 Advanced Dev Kit

Microsemi Corp. has announced a new larges-density, low-power SmartFusion2 150K LE SoC FPGA Advanced Development Kit. It’s meant for board-level designers and system architects who need to rapidly create system-level designs.

Source: Microsemi Corp.

Source: Microsemi Corp.

The kit’s features include:

  • Largest 150K LE development device
  • 2x FMC connectors (HPC and LPC)
  • Purchase of kits comes with a free one-year Libero SoC design software platinum license (valued at $2,500)
  • DDR3, SPI flash
  • 2× Gigabit Ethernet connectors
  • SMA connectors
  • PCIe x4 edge connector
  • Power measurement test points

Source: Microsemi

 

Liberally Apply Test Points (EE Tip #144)

When I first started designing, I did not understand the need for the scope posts for hardware test points. I could always tack on a wire or, with many through-hole parts, connect my scope right to the chip. But now test points are essential. My eyesight and steady hands are long gone. But it goes way beyond that. Many of the scope points are buried under the chips. And those that are exposed are smaller than grains of sand. Provide yourself access to the critical points.

Thinking about where you’ll want to probe the  software can also be useful. Linux has done a great job by providing hundreds “test points” for the OS. We should learn to do that with our applications. Planning in advance the places you want to test is also a useful exercise in the whole development cycle because early on it forces you to think about testing.—Bob Japenga, CC25, 2013

Electrical Engineering Innovation & Outreach

Bill Porter is a Panama City Beach, FL-based electronics engineer working for the US Navy. When he isn’t working on unmanned systems for the Navy, he spends his time running an engineering-focused educational outreach program and working on his own projects. In this interview, Bill talks about his first designs, technical interests, and current projects.

CIRCUIT CELLAR: You’re an electronics engineer for the United States Navy. Can you describe any of the projects you’re involved with?

BILL: I work with unmanned systems, or robots that are teleoperated and/or autonomous. This includes systems that swim under water, on the surface, or across the land. The Navy is working hard to develop robots to do the jobs that are dirty, dangerous, or dull and help keep the sailor out of harm’s way. One such system is called MUSCL, or Modular Systems Craft Littoral. MUSCL is a small, man-portable surface vehicle that is used by Riverine Patrol for remote surveillance and reconnaissance. I was the lead electrical engineer for the project.

Besides robots, I am also working on a few education outreach programs that work towards getting more students interested in STEM careers.

CIRCUIT CELLAR: Tell us about The Science Brothers nonprofit outreach program. How did the program start?

BILL: The Science Brothers is my main educational outreach program run out of my Navy base. For two Fridays every month, a few of my coworkers and I will visit a local elementary school to put on a show. The script of the show centers on the dynamics of two brothers, who specialize in different fields and argue over whose science is “cooler.” The result is a fun and wacky trip exploring different premises in science, such as light, sound, and energy, with examples and demonstrations from the realms of chemistry, physics, and electricity.

Science Brothers show

Science Brothers show

The program restarted when a few coworkers and I sat down and decided to bring back an old program that had existed on the base in the ‘90s called “Dr. Science.” The goal of the program was to bring science-based experiments to the schools using equipment they otherwise were not able to afford. By wowing the students with the spectacular-looking demos, we get them excited about science and yearning to learn more.

CIRCUIT CELLAR: Your website (BillPorter.info) includes projects involving 3-D printing, motor controllers, and LEDs. What types of projects do you prefer working on and why?

BILL: I am a hardware guy. I love to fire up my favorite PCB CAD software just to get an idea out of my head and on the screen. I do not breadboard very often, as I would rather take my chances trying some new idea on a board first. Either it works, or I have an excuse to design another PCB. Thankfully, group-order PCB services have enabled my addiction tinkering at a very low cost. I wish I was stronger at mechanical CAD design to really get the full potential out of my 3-D printer, but I have done well enough without it. It really does come in handy at times, whether it is a quick project enclosure, a mount, or a part for our garden.

Bill is self-proclaimed "hardware guy"

Bill is self-proclaimed “hardware guy”

CIRCUIT CELLAR: Do you have a favorite project?

BILL: Yes! My wedding of course! I married the girl of my dreams who is just as much as a geek as I am, and as a result, we had an extremely geeky wedding over a year in the making involving many projects throughout. So much so that our theme was “Circuit and Swirls” and we carried the motif throughout.

Wedding gadgets

Wedding gadgets

We designed and made our own wedding invitations involving LEDs, a microprocessor, and a clever Easter egg. Furthermore, we 3-D-printed our centerpieces, built up our own “e-textile” wedding attire with LEDs and EL wire, and we even had a “soldering ceremony” during the event. It made our parents nervous, but in the end, everyone had a good time. Did I mention I asked her to marry me on a PCB she designed for a project?

EE-themed wedding invitations

EE-themed wedding invitations

CIRCUIT CELLAR: Are you currently working on or planning any projects? Can you tell us about them?

BILL: I have one main project that is taking up all my time at work and at home. A coworker and I are the technical directors for the first-ever Maritime RobotX Challenge. The challenge, sponsored by Association for Unmanned Vehicle Systems International (AUVSI) Foundation and by the Office for Naval Research (ONR), will take place this October in Singapore. It will include 15 teams of college students from five participating nations and put them to the test by challenging them to design a robot that will complete five tasks autonomously. As one of the technical directors, I have been helping design and build the interactive course elements that the teams’ robots will be facing. Find out more at Robotx.org.

CIRCUIT CELLAR: What new technologies excite you and why?

BILL: I have always been infatuated by LEDs and ways to conserve energy, so I am most excited to see how efficient LEDs are starting to take over as the new source of light in the household.

The complete interview appears in Circuit Cellar 291 (October 2014).

The Future of Temperature-Compensated Crystal Oscillators

Most modern digital and analog electronic devices require a time base to perform their intended function. Found in everything from cell phones to smart munitions, quartz crystal oscillators are widely used in many embedded applications. Quartz resonators’ high Q, excellent temperature performance, and superior long-term aging makes them the clear resonator of choice for many applications. The frequency versus temperature performance of a discrete LC oscillator will be on the order of several hundred parts per million (ppm) per °C, where a crystal oscillator (XO) will have roughly ±30 ppm over the entire industrial temperature range (–40 to +85°C). While being superior to a discrete oscillator, this temperature stability is not nearly sufficient for many modern applications.

EsterlineFigure1

Source: John Esterline

The temperature-compensated crystal oscillator (TCXO) employs the use of an open loop compensation circuit to create a correction voltage to reduce the inherent frequency versus temperature characteristic of the crystal. The crystals used in TCXOs have frequency versus temperature characteristics that approximate a third-order polynomial, as seen in the nearby figure.

The early designs for TCXOs employed a network of thermistors and resistors to create a correction voltage. By using thermistors with different slopes and properly selecting the fixed value resistors, the correction voltage can be made to have a shape factor matched to the crystal’s frequency versus temperature performance. The correction voltage is applied to a varactor in the feedback path of the TCXO. This change in capacitance in the feedback path alters the tuning of the oscillator, thus changing the output frequency and compensating it for temperature effects. Thermistor/Resistor network TCXOs can achieve frequency versus temperature stabilities of around ±1 ppm over the industrial temperature range; however, they are limited in their curve-fitting capabilities because of the nature of using discrete thermistors and resistors.

Thermistor/resistor network TCXOs are still found in specialized environments including satellite and other space applications where modern solid-state devices do not have the radiation hardness to survive. Most TCXOs manufactured today utilize an ASIC which contains the oscillator circuit and a third- or fifth-order polynomial voltage generator. The polynomial generator is an analog output voltage but also has digital registers for setting the coefficients of the polynomial. The newest generations of TCXO ASICs can provide temperature performances of ±0.1 ppm over the industrial temperature range. This is a 10-fold improvement over what is obtainable with a traditional thermistor/resistor network TCXOs and also has the advantage of a much smaller footprint (5 mm × 3.2 mm).

Some high-precision applications require frequency versus temperature stabilities better than ±0.1 ppm. To meet these challenging specifications a different methodology is implemented. An oven-controlled crystal oscillator (OCXO) uses a heater circuit and thermal insulation to keep the crystal at an elevated temperature (≈15°C above the upper operating temperature limit). By controlling the crystal’s temperature and keeping it nearly constant, the frequency deviation due to ambient temperature changes is vastly reduced. OCXOs can achieve frequency versus temperature stabilities of ±0.005 ppm. This improved performance comes at the cost of a larger footprint and increased power consumption. The TCXO’s performance limit of ±0.1 ppm is due to several factors. First, the resonators are not perfect. Their frequency versus temperature stability approximates a third-order polynomial; however, higher order effects are present. Secondly, the polynomial generator is nonideal and induces some higher order artifacts, leaving the user with residuals of ±0.1 ppm. A new methodology which uses an artificial neural network (ANN) to create the correction voltage has recently been demonstrated. The ANN is superior in that the neural network is not inherently shape limited like a third-order polynomial. If enough data is presented to the ANN, it can “learn” the crystal’s temperature performance shape and correct for it. This new methodology has been shown to provide ±0.01 ppm frequency versus temperature stability over the industrial range. The ANN algorithm can achieve OCXO temperature performance in a much smaller footprint, and without the need for the power-hungry oven.

The evolution of quartz crystal time bases over the last 70 years has seen the frequency versus temperature stability improve by a factor of several thousand. As our need for more stable oscillators in smaller packages with less power consumption grows, the development of better compensation schemes is paramount. The ANN demonstrates a technology that has much potential. Its ability to adapt and change its shape factor makes it ideal for complex compensation problems.

EsterlinePhotoJohn Esterline is the CEO of Esterline Research and Design, LLC, a Pennsylvania based start-up company. John holds an MEngEE and a BSEE from Pennsylvania State University. His research interests focus on temperature compensation algorithms for the improvement of embedded time bases. John is the inventor on two US patents (US8188800 B2, US8525607 B2), and the inventor of one patent pending (US 13/570,563). Esterline Research and Design, LLC offers consulting services in frequency control, test and automation and other subject matter in addition to its RF testing products.

 

Circuit Cellar 291 (October 2014) is now available.