In which range is the Voltage (Measured between GND and the PIN) on a INPUT pin from a Arduino (3.3V or 5V, Atmega328).
<0.3 x Vcc = Low, >0.6 x Vcc = High.
In between, could be interpreted either way.
And if it is a LOW Output?
Up to 0.9 at 20mA sink current.
Lower for lower currents.
See Section 29 of the datasheet.
I have a Transistor and when i Set the pin to low, then 20mA are still on (30Ohm Resistor).
Schould I add a Schottkey to drop the 0.2V or how can i do it.
Its a Battery driven Project so 20mA are to high.
Show your circuit, and datasheet for the transistor.
It's possibly miswired, or the wrong transistor is being used.
What happens if you short out D1 and remove R1?
without R1 and D1, in real ther are 0.2V at the base and from Tastkopf1 to collector 20-30mA.
Perhaps your transistor is damaged then. Do you have another?
You don't have any pins swapped around?
I have used simple transistors like that to control strings of LEDs from 12V sources.
If 20-30mA were allowed to flow, the LEDs would be on.
Thx for your Help, i will try it tomorrow.