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

Data Acquisition Issues (2 Free Downloads)

As Maurizio Di Paolo Emilio noted in his essay “The Future of Data Acquisition,” data acquisition “is a necessity, which is why data acquisition systems and software applications are essential tools in a variety of fields.”

For a limited time, we’re sharing two past Circuit Cellar Data Acquisition issues (CC266 and CC278), which you can download for free. These two free downloads will be available only until Friday, September 19.


Issue #266 September 2012

  • TASK MANAGER—The Ubiquitous Importance of Data, p. 2
  • QUESTIONS & ANSWERS—Embedded Systems Education: An Interview with Miguel Sánchez, p. 28
  • MCU-Based Environmental Data Logger, by Brian Beard, p. 18
  • DesignSpark chipKIT Challenge Winners, p. 32
  • Miniature Accelerometers: DIY Acceleration Data Acquisition, by Mark Csele, p. 38
  • EMBEDDED SECURITY—Hardware-Accelerated Encryption, by Patrick Schaumont, p. 48
  • THE CONSUMMATE ENGINEER—Project Configuration Control: Family Tree Drawing & Document Archiving, by George Novacek, p. 58
  • LESSONS FROM THE TRENCHES—Software & Design File Organization, by George Martin, p. 62
  • FROM THE BENCH—Flowcharting Made Simple: Use the Flowcode Flowcharting IDE to Write Code, by Jeff Bachiochi, p. 66
  • PRIORITY INTERRUPT—Managing Expectations, by Steve Ciarcia, p. 80

Issue #278 September 2013

  • QUESTIONS & ANSWERS—Electronics Entrepreneur: An Interview with Jack Ganssle, p. 10
  • Rubik’s Cube-Solving Robot, by Nelson Epp, p. 24
  • Raspberry Pi I/0 Board (Part 2): ISO-Pi Circuit Description and Firmware, by Brian Millier, p. 32
  • Experiments in Developmental Robotics (Part 1): Artificial and Evolving Neural Networks, by Walter O. Krawec, p. 42
  • THE CONSUMMATE ENGINEER—Battery Basics (Part 1): Battery Types, by George Novacek, p. 48
  • ABOVE THE GROUND PLANE—Pulsed LED Characterization, by Ed Nisley, p. 54
  • GREEN COMPUTING—Energy-Efficient Cooling Strategies for Servers Analyze and Control Leakage and Fan Power, by Ayse Coskun, p. 60
  • FROM THE BENCH—Serial Displays Save Resources (Part 3): BMP Files, by Jeff Bachiochi, p. 64
  • TECH THE FUTURE—Electronics Beyond Silicon, by Jeremy Ward and Oana Jerchescu, p. 80

DIY Dead Man’s Switch (No Microcontrollers)

A “dead man’s switch” (abbreviated here as DMS) is a very useful device for applications where the effect of forgetting to turn something off ranges from a mild annoyance to costly or dangerous consequences. We first learned about the DMS from a locomotive engineer, who explained vividly that an engineer is supposed to press a button every minute to keep the locomotive going, otherwise the machine stops. Less “dramatic” applications include turning off lights or other equipment after a period of time.

The ideal DMS provides several minutes of “on” time, requires no programming, external controls, additional power supplies and no modifications of the existing equipment. In effect, no changes should occur in the standard operating procedures of using the equipment. To reset the timer from “off” back to “on,” it is desirable to either use a button or just cycle the power.

Ironically, a multitude of electronic timers available online or at home improvement retail stores are highly over-engineered. These timers either require programming of specific date-times to be “ON” or have very long pre-sets, require changes in equipment wiring, etc.


This article presents a DMS design that has been tested and currently in use in two different systems. One is controlling a UV source and another is controlling a hydrogen gas line valve. If someone forgets to turn off the UV source, the repairs are costly. When it comes to forgetting to turn off hydrogen, a violent explosion may happen!

The DMS works as follows. First, there are no microcontrollers—just plain physics. Capacitors C1 (bipolar, electrolytic) and C2 make a voltage divider (see Figure 1). Note this timer was originally designed for the European voltage; however, it is very simple to recalculate the capacitor divider for the US voltage.

Figure 1: This is the timer schematic. The Reset button S1 is optional.

Figure 1: This is the timer schematic. The Reset button S1 is optional.

The voltage is rectified by a bridge and smoothed by C3. The voltage on C3 is approximately 13 V. When the timer is powered on, both capacitors C4 and C5 are quickly charged each to a half of the supply voltage. FET is turned on and relay is engaged. At the same time, the charge begins a slowly redistribution between the capacitors, with C5 discharging via R3 and C4 further charging. Note that diode D1 is not conducting. When C5 is discharged enough, FET is turned off. This causes the relay to disengage. The timer will continue to be in this state as long as the power is provided, because C4 is effectively blocking any current flow. If the power is removed, D1 opens up to discharge C4 via R2. Remember: C5 is already discharged. Thus, the timer is reset to its initial condition. In addition, a manual reset switch S1 is added in case if it is more convenient to reset the timer by pushing a button rather than briefly disconnecting the mains power.


With the indicated components, the “on” time is for approximately 6 minutes. Changing C4 and C5 adjusts the “on” time. Our hydrogen valve control system uses capacitances of 30 µF each, resulting in approximately 25 minutes of “on” time. Note that the capacitances of C4 and C5 must be the same.


Dr. Alexander Pozhitkov has an MS in Chemistry and a PhD in Genetics from Albertus Magnus University in Cologne, Germany. For 12 years he has been involved with interdisciplinary research relating to molecular biology, physical chemistry, software, and electrical engineering. Currently, Dr. Pozhitkov is a researcher at the University of Washington, Seattle. His technical interests include hardware programming, vacuum tubes, and high-voltage electronics.

Hans-Joachim Hamann is a staffer at the Max Planck Institute for Evolutionary Biology.


Solar-Power the Circuit Cellar (Free Download)

In the spirit of DIY engineering and solar power innovation, we’re re-releasing Circuit Cellar founder Steve Ciaria’s three-part series, “Solar-Powering the Circuit Cellar.”

An excerpt from the first article in the series appears below. And for a limited time, you can download the entire series for free. Enjoy!

The photos show the roof-mounted solar panels that produce approximately 40% of the total PV power. I know it sounds like a joke that the first PV system consideration is walking around the house and looking for the sun, but you can’t generate much energy if your panels are always shaded. When you live in the middle of the woods, finding the sun is often easier said than done.

Approximately 4,200 W of PV power is generated from 20 roof-mounted SunPower SPR-210 solar panels. The other 6,560 W comes from pole-mounted arrays behind this area.

Approximately 4,200 W of PV power is generated from 20 roof-mounted SunPower SPR-210 solar panels. The other 6,560 W comes from pole-mounted arrays behind this area.

Array orientation determines how much energy you can produce. Solar panels are typically aimed due south at a specific tilt angle that optimizes the incidence angle of the sunlight striking the panel. Maximum energy is produced when this tilt angle is equal to the latitude of the location (reduced by a location correction factor). Typically, the optimal tilt angle during the summer is the latitude minus 15°, and the optimal angle for the winter is the latitude plus 15°. Hartford, CT, is located at 42° latitude and the optimum tilt angle (minus an 8° correction factor) ranges from 19° in the summer (34° – 15°) to 49° in the winter (34° + 15°). The Connecticut rebate program suggests that if a fixed tilt is used, it be set at 35°. Of course, these are computer-generated optimizations that don’t necessarily accommodate real-world conditions. While it requires some nontrivial computer calculations to show authenticity, it is my understanding that as long as the non-optimal differences in azimuth and tilt are less than 20°, the loss in maximum power production is typically only about 5%. It is exactly for that reason that the most cost-effective PV installation is typically a fixed-pitch roof-mounted array.

Team installing solar panels on Steve Ciarcia's roof

Team installing solar panels on Steve Ciarcia’s roof

My system includes both variable and fixed-pitch arrays. The roof-mounted panels are located on the solarium roof and oriented at a fixed pitch of 17.5° facing SSW (see Photo 1). According to Sunlight Solar Energy’s calculations, efficiency is still about 92% of the desired maximum because the 17.5° roof angle actually allows higher efficiency during longer summer hours even though it isn’t the optimum tilt for winter.

Pole-mounted arrays are more efficient than a fixed-pitch roof array by design. My configuration is single-axis adjustable. The pole-mounted arrays are oriented due south and enable seasonal adjustment in the tilt angle to optimize the incidence angle of the sun. For everyone ready to e-mail me asking why I didn’t put in a tracking solar array since this is a pole mount, let me just say that you can also send me financial contributions for doing it via the magazine.—Steve Ciarcia, “Solar-Powering the Circuit Cellar (Part 1: Preparing the Site),” Circuit Cellar 209, 2007.

Check out some of Circuit Cellar’s other solar power-related articles and projects:

The Future of 3-D Printed Electronics

Three-dimensional printing technology is one of our industry’s most exciting innovations. And the promising field of 3-D printed electronics is poised to revolutionize the way engineers design and manufacture electrical systems for years to come. In the following essay, Dr. Martin Hedges of Neotech AMT presents his thoughts on the future of 3-D printed electronics.

Three-dimensional (3-D) printing for prototyping has been around for nearly three decades since the introduction of the first SL systems. The last few years have seen this technology receiving considerable attention to the point of hype in the mainstream media. However, there is a new emerging 3-D printing market that is increasing in importance: 3-D printed electronics (3-D PE). Whilst traditional 3-D printing builds structural parts layer by layer, 3-D PE prints liquid inks that have electronic functionality on to existing 3-D components. 3-D PE is achieved by combining advanced printing technologies, such as Aerosol Jet, with specially designed five-axis systems and advanced software controls that allow complex print motion to be achieved. The integrated print systems allow the full range of electronic functionality to be applied: conductors, semiconductors, resistors, dielectrics, optical, and encapsulation materials.

These can be printed on to virtually any surface material of almost any shape. Once deposited the inks are post processed: sintered, dried, or cured to achieve their final properties. Multiple materials can be printed to build up functionality, or surface mount devices (SMD) can be added to make the final electro-mechanically integrated system (see Photo 1).

Photo 1: 3-D PE demonstrator—Tank-filling sensor produced in the FKIA project funded by the Bavarian Research Foundation (Courtesy of Neotech AMT GmbH)

Photo 1: 3-D PE demonstrator—Tank-filling sensor produced in the FKIA project funded by the Bavarian Research Foundation (Courtesy of Neotech AMT GmbH)

In this example, two capacitive sensor structures have been printed on the ends of an injection-molded PA6 tank. The sensors are connected by a printed circuit (conductive Ag) and SMD components are added to complete the device. When water is pumped into the tank, the sensors register the water level as it rises, lighting the LEDs to indicate the fill level. When the tank compartment is full, the circuit senses the water fill level and reverses the pump direction.

3-D PE has the potential to provide enormous technical and economic benefits in comparison to conventional electronics based on 2-D printed circuit boards. It allows the combination of electronic, optic, and mechanical functions on shaped circuit carriers. Therefore, it enables entirely new product functions and supports the miniaturization and weight-saving potential of electronic products. By eliminating mechanical components, process chains can be shortened and reliability is increased. As a digitally driven, additive manufacturing process materials are only applied where needed, improving the ecological balance of electronics production. With no fundamental limitation on substrate material, the user is able to select low-cost, easy-to-recycle and more environmentally friendly materials. The novel design and functional possibilities offered by 3-D PE and the potential for rationalization of production steps indicate a potential quantum leap in electronics production.

Advances in this field have been rapid since the first developments that focused on 3-D chip packaging. In this field, printing is conducted over small changes in z-height to connect SMDs. Photo 2 shows an example where wire bonds are replaced by printing interconnects, from the PCB, up the side of a chip, and over onto the top contact pads.

Photo 2: 3-D chip packaging (Courtesy of Fraunhofer IKTS)

Photo 2: 3-D chip packaging (Courtesy of Fraunhofer IKTS)

Such applications only require  relatively simple print motion. The current “state of the art” is to use five axes of coordinated  motion  to  print high complex shapes. This capability enables the production of truly 3-D PE systems, such as a 3-D antenna for mobile devices (see Photo 3).

Photo 3: 3-D printed antenna (Courtesy of Lite-On Mobile)

Photo 3: 3-D printed antenna (Courtesy of Lite-On Mobile)

This application is well advanced and moving towards high-volume mass production driven by the benefits of a flexible manufacturing, novel design capabilities, and cost reduction compared to the current methods based on wet chemical plating processes. 3-D PE is also being scaled to print on large components beyond the size range possible with current manufacturing methods. For example, in the automotive field, 3-D prints of heater patterns are being developed for molded PC windscreens of up to 2 m × 1 m in size.

Currently, 3-D PE applications are mainly limited to circuits, antennas, strain gauges, or sensors using conductive metal as the print media with additional electronic functionality being added as SMDs. However, the technology also has the potential to leverage new material and process developments from the printed and organic electronics world. In this field, many different material systems are currently being applied on planar surfaces to create multi-material and multi-layer devices. Functionality such as resistors, capacitors, sensors, and even transistors are being incorporated into fully printed 2-D electronic systems. As these print materials and processes mature, they can be adapted to 3-D applications. It is expected that the coming years will see a rapid increase in the range of fully printed 3-D electronic devices of novel functionality.


Dr. Martin Hedges (mhedges@neotech-amt.com) is the Managing Director of Neotech AMT GmbH based in Nuremberg, Germany. His research includes aspects of additive manufacturing, materials and processes. His company projects focus on the development of integrated manufacturing systems for 3-D printed electronics.

Circuit Cellar 290 (September 2014) is now available.


Advanced Data-Logging Application

Measurement Computing Corp. (MCC) recently announced the release of DAQami, an advanced data-logging application that enables you to acquire, view, and log data from MCC USB DAQ devices.

DAQami currently supports over 40 MCC hardware devices

DAQami currently supports over 40 MCC hardware devices

In less than 5 minutes after installing DAQami and plugging in a DAQ device, you can create an automatic configuration and acquire live data, MCC noted in a release.

Data can be acquired in volts and degrees, as well as custom units with linear scaling. Channels can be viewed on any combination of scalar, strip, and block displays. Once data is acquired and logged, you can use DAQami to review the saved data file.

The DAQami user interface is flexible and provides the ability to customize display size and location, zoom factor, and channel/trace colors. You can configure MCC DAQ hardware within the application, selecting sam­pling rate, start and stop triggers, and sample count.

DAQami currently supports over 40 MCC hardware devices including the $99 100-ksps USB-201 DAQ device.

DAQami costs $49 when purchased with MCC DAQ hardware.

Source: Measurement Computing Corp.