Ground as Input

Using Arduino LEDs and Multiplexing
#1

Can I use a ground as an Input Signal?

I want to create a VVL Controller for vehicle, but I want to Impliment a few LED's into the circut, which is easily enough done.

Basically I want if say pin 3 Begins to Ground (which would be an Input), switch pin 10 (led) on, and same again on another few pins?

#2

Depends on what the device is that pulls the signal low on the input pin. You may need external pullup resistors or enable the internal ones on that pin 'pinMode(3,INPUT_PULLUP);' Then the digital input will go low when grounded by the external signalling device, you would check this with something like 'if (digitalRead(3) == LOW)'

#3

Have a look at this:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

#4