I want to turn a 5kW Motor on and off with an Arduino.
The motor is connected to a Siemens Sirius Soft starter, which should make the task relatively painless.
The Softstarter has 3 input terminals:
- Plus is connected to 24V DC
- Switch/Signal: if set to 24V, then the motor will be running, if set to GND, then the motor stops.
- GND is connected to Ground
Because the Arduino runs on 5V, but the Softstarter needs a 24V signal, so I thought it would be a good idea to use a darlington transistor.
I used a TIP120 NPN Transistor (datasheet here) and I built the following:

Unfortunately, this does not work. I set the Pin11 to HIGH, but the Emitter leg of the dalington still still has a GND Potenial.
I searched the internet and found your video on youtube. Now I suppose that the problem is caused by the fact that I am using the wrong type of Darlington transistor. The TIP120 is not suitable for a source configuration.
A TIP125 would be a better choice.
Is this the reason my schema does not work? Any other thoughts?