Solar Monitor

A simple solution to prevent a solar powered LoRaWAN gateway from going into brownout when the batteries drop in voltages.

The Backstory

I have a solar powered Raspberry Pi + RAK2245 + RAK2013 that has a problem where when it gets cold out, the batteries don't have the Amps to power the gateway when the sun comes up. This puts the gateway into a brownout state where the cellular module disconnects and will not reconnect until the system is rebooted.

I have learned that a few minutes delay will resolve this issue, allow the batteries to charge and the system to boot correctly. This project is an attempt to automate this task.

Theory of Operation

When the voltage drops below about 3 volts, the MCP102-300E/TO will sit it's pin 2 LOW, once the voltages has stablized above 3 volts for more then 120 ms, pin 2 goes HIGH.

The PIC16F15214-I/P microcontroller reads the input from pin 2 on the MCP102-300E/TO (via pin 2 [INT] on the microcontroller) and set pin 0 LOW. When microcontroller pin 0 is LOW, the PN2222A disables the power to the output pins of the board.

Software

• KiCad EDA - Version 6.0.2 - The Schematic & Board softare
• MPLAB X IDE - Version 6.0.0 - Software used to build the C code
  • XC8 - Version 2.32 - The C compiler (A part of MPLAB X IDE)

Hardware (BOM)

Identifier	Qty	Part #	Description	DigiKey
U1	1	PIC16F15214-I/P	Microcontroller	150-PIC16F15214-I/P-ND
Q1	1	PN2222A	Transistor	PN2222AFS-ND
Q2	1	MCP102-300E/TO	Voltage Supervisor	MCP102-300E/TO-ND
C1	1	10pF	Ceramic Capacitor	K100K15C0GF53L2-ND
D1	1	1N914	Diode	1N914FS-ND
RV1	1	PV36W103C01B00	10K Ohm Trimmer	490-2875-ND
SW1	1	1825910-6	Push Button - 6mm	450-1650-ND

Schematic

Board

The Top of the Board

The Bottom of the Board