UUGear Witty Pi 4 - The Unpopulated 2 X 3 Pin Headers (P4)

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The signal should be a positive pulse. Processing a pulse will be equal to taping the switch once, so
it will turn on your Raspberry Pi when it is off, or turn off your Raspberry Pi when it is on.
CATH / CATHOD
It is the cathode (ground) for Raspberry Pi. There is a 0.05 Ohm sampling resistor between CATHOD
and GND, to measure the actual output current.
If you measure the voltage between cathode and ground as V
k
, you can calculate the actual current
with this formula:
I
out
= V
k
/ 0.05 = 20 * V
k
GND
It is the ground of Witty Pi 4 board, and it directly connects to the GND wire of power supply.
11.3 The Unpopulated 2 x 3 Pin Headers (P4)
This is the In-Circuit Serial Programming (ICSP) header for uploading the firmware to the micro
controller. You can find the same ICSP header on many Arduino boards. The details about how to
use this header can be found in this tutorial.