Digital Input LED

Forum 2005-2010 (read only) Hardware Interfacing
1

Like the LED on PIN 13 that turns ON when that pin is set to OUTPUT, I am looking for a way to have a LED that turns ON when that pin is set to INPUT. My idea is to have the reverse of the PIN 13 LED which is currently:

PIN 13 --> 1k resistor --> LED --> GND

to the following for it to turn on when it is set to INPUT:

PIN 13 <-- LED <-- 1k resistor <-- +5V

but there is a problem: as it is waiting for an input, the LED would be constantly ON and it could be mistakenly taken as an INPUT signal :(. What can I do so that I can have both LEDs but one of them turns on when a signal is going out and the other when a signal is going in without affecting the signals?

2

PIN 13 --> 1k resistor --> LED --> GND

to the following for it to turn on when it is set to INPUT:

PIN 13 <-- LED <-- 1k resistor <-- +5V

That just changes the LED for a current source drive to a current sink drive.

There is nothing electrically different at the pin, when it is being driven by an input device, to a pin driving an output device. So therefore you can't implement what you want. Sorry.

3

Unclear what you're trying to do.
Did you mean something like this?

4

He wants an LED to indicate when a pin is set up to be an input and another LED to indicate when it is set up to be an output.

He wants to sense the conditions on the pin itself to do this.

5

Ah!
OK.

6

Ok, Np...

Thanks guys...