Remote Power Switch for RatRig 3D Printer (and maybe other devices)

 There is great project octoeverywhere that allows to control and monitor your RatRig and other printers remotely, you can start/pause/stop even shut down your printer but shut down doesn't mean cutting AC power, AC adapter still works and your boards are under voltage. Here is very easy solution to solve this problem, the circuit I've made really powers off the printer.  You will need:

1.  one SSR (solid State Relay), I've used Omron DV24v in /AC220v SSR. You can use any that supports ac voltage and current your printer consumes (excluding bad heater). 
2. one Photocoupler, I've used TLP521, you can use any, that works with 3v , even transistor is ok.
3. Any small led
4. Switch push button for AC high voltage.

You can choose any free GPIO of Pi (I've used 17) and connect it to photocoupler via resistor (in my case 380Ohm), then photocoupler drives SSR with indication led in serial. This led will show state ON.

To turn on your printer, you should press START push button until Pi loads and send ON signal to GPIO 17, you'll see the led go ON, after that you can release the button, SSR will hold the power until Pi receives command to turn off , that will cause SSR off and power cut.

The best way to control this GPIO 17 is via Moonraker, just add this to moonraker.conf:

[power psu]

type: gpio

pin: gpio17

off_when_shutdown: True

initial_state: on

How will it work -   you shut down printer via Dashboard shutdown command, Pi starts shutting down safely and when of, GPIO17 goes 0. When Pi is loaded, GPIO is 1 (ON) all the time that keeps SSR open.