Making your projects more reliable


Connecting an external watchdog to your Raspberry Pi and Arduino fixes many of the problems suffered by the internal watchdog. However, the examples here do not power cycle the device. In some rare cases, it might not bring your computer back from the dead, just as the internal watchdogs won't.

If you need to go an extra step, you can hook up either a MOSFET switch or a relay to the "Pulse High on Timeout" Dog outputs and switch off the power to the Arduino or Raspberry Pi for 500ms. Doing this will perform a complete reset and handle these odd cases, which you certainly can't do easily with the internal watchdog. You can even string both watchdogs together to control a bistable relay, which takes no current to maintain in one state or another. My favorite kit for an inexpensive bistable relay is made by Ciseco [8].

Next Time

My next column will be a tutorial with examples on how to use an inexpensive USB-based logic analyzer to debug your circuits and see what is happening on your board. What once was a $20,000 box can now be had for $200 and hooked up to a PC.

If you have a suggestion for a column or would like to see a specific board or product reviewed, please send email to If you have specific questions, please post on the SwitchDoc Blog [7] so everybody can learn from your question. I'll be picking the best question and answering it the next SwitchDoc Labs column.

Reader Question

Question: With the Arduino, we see lots of different companies producing many different versions. Why don't we see that with the Raspberry Pi?

Answer: The Arduino has no proprietary parts, so anybody can build a better, faster, cheaper, or lower quality unit. It's a wild world out there. The schematics and all the software are completely available. In fact, in one of our next projects, I will be adding an on-board Arduino Uno-compatible processor because of the great tool chain available for development.

Although the Raspberry Pi software is freely available, because of the Raspberry Pi Foundation's agreements with the BCM2835 manufacturer, the most important part is not. This is both good and bad. You get an excellent, low-cost, high-quality supplier in the Raspberry Pi Foundation, and the boards are consistent and work with each other, but without competition between various companies.


  1. "Pi on Wind" by John C. Shovic, Raspberry Pi Geek, issue 04, pg. 8:
  2. "WeatherArduino" by John C. Shovic, Raspberry Pi Geek, issue 07, pg. 62:
  3. Kwartzlab makerspace:
  4. "SwitchDoc Labs: Real-Time Clocks" by John C. Shovic, Raspberry Pi Geek, issue 08, pg. 80,
  5. Eagle PCB software:
  6. DFRobot:
  7. SwitchDoc Labs:
  8. Bistable latching relay kit:

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