The Juice4halt module uses the GPIO header of the Raspberry Pi for communication and for supplying the Raspberry Pi with power.
is used for detecting if the Raspberry Pi is powered up. The GPIO25 is disconnected when the voltage at this pin falls to 0V.
Pins2, 4 (5V)
5V backup power for Raspberry Pi
3.3V logic signal for bidirectional communication between the Raspberry Pi and the Juice4halt. The Raspberry Pi reports the following states:
- Boot process completed
- Shut-down process completed
In the other direction, the Juice4halt forces the Raspberry Pi to shutdown when the charge state of the supercapacitors is too low
Pins 6,9,14,20,25 (GND)
All other pins are not used
In the future versions the Juice4halt will contain a Real-Time-Clock circuit and a RS485 interface. These extensions will occupy the UART pins 8,10 and the I2C pins 3,5 of the Raspberry Pi GPIO interface