External input to pin

Projects General Guidance
1

Is it possible to achieve the reverse of what this tutorial is describing:

http://arduino.cc/en/Tutorial/InputPullupSerial ?

I.E. Instead of using ground to change the input, use +5V for example. The reason I ask is because I need to check if there is voltage from an external source in order to satisfy my condition...

2

Yes, it is possible but not using Software. Just add an external pull-down resistor and you have what you're looking for.

3

Describe the external signal source. What I mean is, is the source either 5V or open (like a push-button wired to 5V) or is the source 5V and ground (like a TTL signal)?

4

groundfungus:

5V & GND. Are you going to suggest I just use the GND of the source? Is it possible?

EDIT:

Sorry misinterpreted your question. Upon better comprehension, yes it is 5V or open.

Pylon:

Thank you for your swift reply, I shall look into pull-downs :smiley: