Which NPN Transistor?

[janCGN]

Hey @killee ,
I have rebuilt the setup so far. Many thanks for the great description.
However, I am currently facing the problem that when "heating=off" the voltage at the SSR is 5V and when I switch it on it drops to 1.9V - so the 5V is only present in the "off" state. Is that normal?
You wrote something about the NPN transistor, can you tell me which one you used?

Thanks in advance

[killee]

I'm so sorry for the late response.

I've used a bc547 with a 1kOhm resistor for the base.

I don't understand exactly where you measure the voltage. Can you describe it a bit?

Regards