Getting more power from your solar panels

Coming Next Column

Next time at SwitchDoc Labs I build an air quality environmental sensor using the Raspberry Pi and – you guessed it – Grove connections and devices [13]. The Raspberry Pi sorely needs a Grove ADS1115 16-bit analog-to-digital device; then, I'll add a Grove air-quality sensor and test it with, of all things, a can of hairspray.

Q & A

Q: Assuming that I understand voltage drop, how long can the cables be from the WeatherPiArduino [11] [12] boards to the WeatherRack Weather Sensors. I did dig around and could have missed it, and it could be provided in documentation when purchased. Based on my guess looking over the design and reading various blog items, it looks like the Pi and WeatherPiArduino boards encased need to be less than 3 meters, more or less. Of course, I could be totally wrong. My goal is closer to 20 meters. I am looking for the recommended maximum distance, so I can then work on resolving this possible problem.

Best regards, Tom

A: Regarding the cables from the WeatherPiArduino board to the WeatherRack, 3 meters is easy. Longer than that has noise issues, but not necessarily voltage drop issues.

Here is what you can do to make the distance longer (in Project Curacao, the cable was 30 meters): Use Cat 10 wire and double the wires. For the rain bucket and anemometer, add another pull-up resistor to 3.3V on the line. It is currently 10Kohm, so adding another 10 or even 5Kohm resistor will make the line less susceptible to noise.

You can also fiddle with the debounce software (increasing the debounce time) to make it less susceptible to noise. For the wind vane, changing the software to average multiple readings will make it less susceptible to noise.


  1. Time lapse video of solar tracking:
  2. " SwitchDoc Labs – Solar-Powered WiFi" by John Shovic, Raspberry Pi Geek, issue 15, 2016, pg. 80,
  3. Grove SunAirPlus (two):
  4. Grove DRV8830 I2C mini motor driver:
  5. Grove I2C four-channel mux:
  6. Small 5V stepper motor:
  7. JST2 to male header conversion cable:
  8. Grove 128x64 OLED display:
  9. Magnetic declination:
  10. Code for this article:
  11. "WeatherArduino" by John C. Shovic, Raspberry Pi Geek, issue 7, 2014, pg. 62,
  12. WeatherArduino erratum:
  13. "SwitchDoc Labs – Grove Devices" by John C. Shovic, Raspberry Pi Geek, issue 16, 2016, pg. 76,

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