Autonomous WLAN Router Experiment: Part 2

I’ve bought some hardware in order to build up the experiment:

  • One monocrystalline 20Wp solar cell (25€)
  • A solar charge controller (15€)

I’ve also built a current/voltage monitoring board, which allows monitoring of the power generated by the solar cell as well as power drawn by the peripherials. Because it also monitors voltage, we can make assumptions of the battery charge status. It uses two INA138 current shunt monitors, together with two 0.1Ω 0.5W 1% precision shunt resistors and a ATMEGA168 (no low power, that’s the one I got at hand). The power monitoring circuit draws less than 10mA at 5V. I have to measure the exact power consumption,   I only recall that the bench PSU was showing 0.00A and my Fluke 27 did show something like 5mA, but I haven’t written down the exact numbers.

So much cool things and then: kaboom! I accidently connected the step-down converter backwards (12V to the output and the 5V router to the input), which delivered 12V straight to the router, which then refused to work. As I couldn’t find any fuse on the router, I assume it is totally bricked and I’ll most likely go with a Carambola2 board, which also requires only 0.5W power.

In the meanwhile, I’ll use a carambola board which uses 1.5W power, but that should be okay until my Carambola2 board arrives.

The current monitoring board can be found at

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