Understanding your data with graphs

Coming Next Column

In the next SwitchDoc Labs column, I will explore the incredible Arduino-based, inexpensive, WiFi-based ESP8266 solution and get it talking to a Raspberry Pi.

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

Questions & Answers

[UCC:interviewer]Q:[/UCC] We are currently struggling with a suitable power management system for our solar power system, and I am wondering if I could get some help. We charge a 12V lead acid battery from a 40W panel. We were looking at a way to detect and store battery voltage and shut down when voltage is low. However, our problem on the flip side is restarting the system once we have gained a suitable battery charge again. How do we make sure that the system will restart properly? Chris – Australia

[UCC:interviewee]A:[/UCC] Power management is one of the biggest challenges SwitchDoc Labs faces with solar-powered projects. A brownout event is always possible. Shutting down and recovering is magic!

The three things SwitchDoc Labs uses are:

  • USB PowerControl [14] for shutting the Raspberry Pi off. Really off – not just a shutdown.
  • INA3221 Breakout board [15] for measuring the voltage and current through the system – three channels of voltage and current. This is the same chip used in the SunAirPlus board.
  • Dual WatchDog Timer [16] to turn on the Pi through the USB PowerControl Board after it has been shut down by software. If you want to learn more about watchdog timers, check out this Raspberry Pi Geek article [17].

You can find out more at:

1. WeatherPi Solar Powered Weather Station Instructable [18].

2. Blog posts about the power management problem [19] [20].

For even more, go to switchdoc.com and search on Solar Power and Brownout.


  1. Project Curacao: http://www.switchdoc.com/2015/08/3-months-in-paradise-project-curacao-happy/
  2. Project Curacao Live: http://www.milocreek.com/projectcuracaographs
  3. RasPiConnect: http://www.milocreek.com/styled-3/index.html
  4. Matplotlib: http://matplotlib.org
  5. MATLAB and Rasp Pi: https://learn.adafruit.com/how-to-use-matlab-and-simulink-with-raspberry-pi/overview
  6. Matplotlib on Rasp Pi: http://wyolum.com/numpyscipymatplotlib-on-raspberry-pi/
  7. Matplotlib options: http://matplotlib.org/contents.html
  8. Project Curacao on GitHub: https://github.com/projectcuracao/projectcuracao/tree/master/graphprep
  9. 3D graphs: http://matplotlib.org/mpl_toolkits/mplot3d/tutorial.html#toolkit-mplot3d-tutorial
  10. "Solar Power Management" by John C. Shovic, Raspberry Pi Geek, issue 10, pg. 32, http://www.raspberry-pi-geek.com/Archive/2015/10/Managing-solar-power-systems-with-SunAir-boards
  11. MySQL tutorial: http://www.arachnoid.com/MySQL/index.html
  12. RasPiConnect wiki: http://www.milocreek.com/wiki
  13. RasPiConnect video: http://www.switchdoc.com/2014/01/project-curacao-raspiconnect-video/
  14. PowerControl board: http://www.switchdoc.com/usb-powercontrol-board/
  15. INA3221 Breakout Board: http://www.switchdoc.com/ina3221-breakout-board/
  16. Dual WatchDog Timer: http://www.switchdoc.com/dual-watchdog-timer/
  17. "SwitchDoc Labs: Watchdog Timer" by John Shovic, Raspberry Pi Geek, issue 09, pg. 86, http://www.raspberry-pi-geek.com/Archive/2015/09/Making-your-projects-more-reliable
  18. Solar Rasp Pi weather station Instructable: http://www.instructables.com/id/Create-Your-Own-Solar-Powered-Raspberry-Pi-Weather/
  19. Power management blog: http://www.switchdoc.com/2015/04/figuring-out-when-to-shutdown-your-solar-powered-raspberry-pi-weatherpi/
  20. Turning the Pi on and off: http://www.switchdoc.com/2015/04/turning-the-pi-on-and-off-weatherpi-solar-power/

Buy this article as PDF

Express-Checkout as PDF

Pages: 6

Price $2.95
(incl. VAT)

Buy Raspberry Pi Geek

Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content