Pin 13 w/ led using with pushbutton.

Forum 2005-2010 (read only) Hardware Interfacing
1

On the arduino duemilanove board, with the led on pin 13, can I still use the pin for a pushbutton?
If so, are internal pullups necessary, or will the led (and resistor?) do that?

2

You have to declare the pin function in the code as either
pinMode(pin13, OUTPUT); or pinMode(pin13, INPUT); so since the LED is an output and the pushbutton is an input you can't connect both of them to it.

3

pinMode(pin13, OUTPUT); or pinMode(pin13, INPUT); so since the LED is an output and the pushbutton is an input you can't connect both of them to it.

Not exactly. You can program pin 13 to be a input pin, however the signal that will drive it will have to be able to source the led current (when the signal is HIGH) which with it's 1k ohm resistor will be around or under 4ma. I think you would also need to enable the internal pull-up resistor to prevent the pin from floating if you are using a simple switch wired to +5vdc, or use a external 10k pull-down resistor as the led will not be biased on when the pin is a input and might float as I said.

Lefty

4

Sorry I wasn't clear: I don't need the led to work, but i wasn't sure if it would interfere with readings.

5

are internal pullups necessary,

Yes

or will the led (and resistor?) do that?

No they don't pull up.