How to set a input pin low?

How to keep an input pin low?

 pinMode(SWITCH, INPUT);
digitalWrite(SWITCH, LOW);

seems this set doesn't work.

Did you define "switch" as a pin number? You must else the poor processor has no idea which pin you are talking about and just keeps on looping :slight_smile:

I'm definitely NOT trying to make fun of your question. We all have to learn so keep asking.

Can this sentence ‘How to keep an input pin low?’ itself be a question even without the code?

How do you know? What are you trying to do?

If the pin is configured as an INPUT , digitalWrite() will enable (HIGH ) or disable (LOW ) the internal pullup on the input pin. It is recommended to set the pinMode() to INPUT_PULLUP to enable the internal pull-up resistor.

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Connect it to ground. Use a resistor, if there is ever a chance that the pin will be declared an OUTPUT, and HIGH.

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I print out the status of the 'SWITCH' pin, that is '1', even when set it be LOW.
I read that paragraph, and asking if there are any solution. maybe in hardware?

Given in reply #5

Inputs are just that; they are connected to a sensor, switch etc.

You use digitalRead( ) to see what logic level is on the pin.

Outputs can be set LOW or HIGH in which case the pin goes to 0V or 5V(3.3V).

A lot of questions…
What Arduino?
Pin 1 is part of the default serial port on a UNO and equivalents.

Seeing the whole code, the schematic, and a description of what you are hoping to do would be an immense help.

I'll do it.

There is also INPUT_PULLDOWN option, depends on hardware