PinInput High & Low Problem, less Voltage

I have the following problem ...
In my circuit, I'm selecting something external as a switch, actually about high & low.
Now I have only 0.3V low
And 0.9V high.
Measurable is the value reached but not the predetermined thresholds ... What can I do?
Do I need to artificially raise the voltage for High or can I get the Arduino to measure 0.9V as high?

Greetings and thanks

Duplicate in the German part of the forum.

I understand you want to measure if a signal is below 0.3volt or above 0.9volt.
You could use an analogue input for that.

Detect if it's above or below ~0.6volt.

if(analogRead(A0) > 122) digitalWrite(somePin, HIGH);
else digitalWrite(somePin, LOW);


Yes, same in both Forums. Thx@all