This guide provides the wiring diagram and description of the Advanced Soft On/Off Board.
The board switches power on and off to your 3v-6v device. It is designed with the Raspberry Pi in mind, but will work with almost any project that uses 5 Amps of power or less. The technical function is detailed here. The board is available for purchase here.
The connections labeled -IN and +IN are for the power input. This can come directly from a 5v power supply, or even from a battery pack. Both the front and back of the board are shown here for clarity only.
The SWITCH connection goes to one side a momentary switch, and the other side of the momentary switch is connected to -IN.
The connections labeled -OUT and +OUT are for the power output. These lead to the device that’s being powered.
The TX pin is used to automatically shut off power to your device after a shutdown process is complete. It needs to be connected to a voltage above 3v to keep the board powered on.
Failure to connect the TX pin to a voltage above 3v will cause the board to shut off 3 seconds after it is powered on.
The GPIO pin is an isolated connection that leads to the power switch. When the switch is pressed, the GPIO pin connects to -IN (also referred to as GND)
This board acts as a soft switch, and switches the positive side of a power source on and off. When it is off, it draws no power.
Basic Function: When the power button is pressed (or the switch pin is momentarily connected to GND in any other manner) the power is switched on. If the power button is then held for 3 seconds the power will be switched off. If this is all that is needed, then the TX pin should be connected to the OUT+ connection. This keeps the board from shutting off automatically after 3 seconds.
Advanced Function: As with the basic function, when the power button is pressed (or the switch pin is momentarily connected to GND in any other manner) the power is switched on. The difference with the advanced function though is the TX pin. This pin should be connected to a point on your device that generates a voltage above 3 volts. On the Raspberry Pi, the easiest pin is the TX pin (hence the label).The TX pin switches to 3.3v when the Pi is powered on, and it switches off when the Pi is shut down. This means that 3 seconds after shutting the Pi down, this board will kill power to it completely until the power switched is pressed again. It also means that the Pi will automatically shut off if there is no SD card or OS installed. The board will also switch off if the switch is held for 3 seconds.
More Advanced Function: This board’s GPIO pin can be used to signal your device to issue a proper shutdown. A pin on the Raspberry Pi can be configured to look for a voltage drop, and then run the shutdown process once it detects this drop. After the Pi is shut down, the TX pin feature will take over and kill power to the device entirely.
Although this board was designed primarily to add soft shutdown to the Raspberry Pi, it is very useful for many projects. I look forward to seeing other uses you guys come up with.