raspi-supercap
Open source Raspberry Pi supercapacitor UPS hat
Goal
Make reliable turn on / shutdown shield for Raspberry Pi
Status
PoC assembly
(!) Not yet tested ;)
BOM
- PCB – https://easyeda.com/adoconnection/raspi-supercap
- 20F x 2 supercapacitors
- ATMega328
- resistors
- diodes
- MT3608 DC-DC Step up converter board
Open questions
- Use special supercapacitor chargers or not? (https://www.analog.com/en/ltc3225) – not in v1
To-Do checklist
- Firmware
- Monitor PI state
- Call shutdown pin
- On power on wait for capacitors to be charged and turn on Raspberry
- I2C slave to query external power status and capacitors charge level
- Reset Raspberry pi if shutdown was activated and power is restored
- Customizable power off behavior
I2C
Default bus address is 0x77 Registers:
| Address | Mode | Default value | Info |
|---|---|---|---|
| 0x01 | R | 0x64 | Test register, always return 0x64 |
| 0x02 | R | External power connected. Return 0x00 or 0x01 | |
| 0x03 | R | Capacitor charge in percents 0 - 100 | |
| 0x04 | RW | 3 | Turn off timeout in seconds. Wait for N seconds before issue a turn off command. |
| 0x05 | RW | 50 | Turn off threshold. Shutdown pi at 50% charge left. |
| 0x06 | RW | 30 | Turn on threshold. Pi boot at 40% charged capacitors. Valid values 0 - 100 |
| 0x50 | RW | 0x21 | I2C address |
Sources of inspiration
- https://juice4halt.com/
- https://www.saveyourpi.com/
- https://www.youtube.com/watch?v=m20o3P-S5s8
- http://www.hackerspace-ffm.de/wiki/index.php?title=Raspi_EDLC_UPS
- https://raspberrypi.stackexchange.com/questions/74641/how-to-make-a-simple-reliable-15-second-ups-for-shutdown
- https://raspberrypi.stackexchange.com/questions/22579/pi-headless-how-to-confirm-that-the-pi-is-shut-down
- https://raspberrypi.stackexchange.com/questions/5489/how-do-i-turn-on-my-raspberry-pi-after-shutdown
- https://code.google.com/archive/p/tinkerit/wikis/SecretVoltmeter.wiki
- https://www.arduino.cc/en/Tutorial/MasterWriter
- https://raspberrypi.stackexchange.com/questions/3704/i2c-library-for-mono-c