Always on, solar powered, stand-alone 24/7 Wi-Fi repeater.

Some simple Wifi router can be configure in repeater. This simple Wifi router didn’t need press any button, just start when the USB charger is working. One example I used is TPlink TL-WR802N. After testing, this router need at least 150mA-200mA full time to work. I developed here a board, with 7000mAh batteries and a control charge with an external solar panel.

The board can have 2 control possible. One is with a standard Maxim comparater MAX931 (or equivalent LTC1440), one for low level, one for high level. The second control possible is with a simple uC, PIC 12F1572. Roughly, the functions are the same but with the uC, the voltage adjustment is easier.

For the DC-DC, to convert the 4.2V lithium batteries to 5V USB, I used an LTC3536. This DCDC IC can provide 1A max and has an real disable function, which is mandatory to avoid leakage from the batteries in the USB. - When the voltage is too low, the solar panel will charge the batteries only. USB output is OFF.

- When the batteries level is around 3.9V, the DCDC is ON and provide 5V to the router, which turn ON automatically.
- If the batteries level are more than 4.2V, the solar panel current is redirect to a power resistance. I didn’t want to add a switch in the charging circuit. There is only a Schotcky diod 2A to charge the batteries.
- If the batteries level goes down to 3V, the DCDC is stopped and the router too.

The solar panel is 5V-10W. I tried with a 5W but it is too short. 5h of sunshine cannot give 19h of power to the router. With the 10W panel, it is working well. 4h-5h sunshine are enough to charge the batteries for another 19h.

The efficiency of the DC-Dc is so-so. It is using 200-250mA full time. The batteries are 2 batteries 18650 3500mA in parallel. Take care of the fake... I had some bad experience here. There is some LED to display the status of the charger.

The PCB is done, to solder the DC-Dc chip is little bit tricky due to small pitch and the solder bad under the chip. For the 12F1572, 2 possible format, DIP8 or SOP8. The software for the 12F1572 is not too complex. Power and LED management.