I’ve moved my printer to another room. Now it’s connected to my continuously running computer. But it’s constantly connected to power and is not really switching off. So I was searching for a solution to switch it of automatically. Using a µC would be nice, but the idea a the moment is to use a USB->serial converter and us the status pin RTS to switch a solid state relay. Today I’ve successfully tested the setup. First I tried with python, which in general is able to set the status of that pin, but unfortunately python is too “high”. During initialization and termination RTS is touched. And I don’t want to “shock” my printer with short switching pulses. But I’ve found this C-code. This allows to keep the state of the pin after termination of the program. This little piece of code exactly does what I need. I’ve added a diode before connecting RTS to the solid state relay to make sure that the relay does not see a negative voltage. I can not yet post a picture of that because my prototype is highly dangerous and I don’t want to provide any examples of dangerous 230V wiring on the net.

The next step will be to set up a cups backend that switches on and off the relay.