Quick question about current draw

Forum 2005-2010 (read only) Hardware Interfacing
1

Is there a way to detect whether or not a pin set as OUTPUT is actually being drawn from

Example.
Lets take a simple LED

case 1.
LED cathode = pin 8
LED anode = pin 9

case 2.
LED cathode = pin 9
LED anode = pin 8

in my setup i set pin 8 and 9 as OUTPUT

lets say that by default my program runs for anode on pin 9
digitalWrite(8, LOW);
digitalWrite(9, HIGH);

is there a way to test if current is actually being drawn from pin 9?
and if not, then reverse and set

digitalWrite(8, HIGH);
digitalWrite(9, LOW);

thanks in advance for tips, hints, tricks and such

2

You could measure the voltage across the current limiting resistor with an analogue input.

3

You could check the datasheet and see if an ADC pin can be used as a digital output
and an analog input. Depending on the current you may be able to measure the voltage drop across the output transistor. This would give you a few pins.

(* jcl *)

www: http://www.wiblocks.com
twitter: http://twitter.com/wiblocks
blog: http://luciani.org

4

the resistor idea sounds like it may work
will try it out

5

You could check the datasheet and see if an ADC pin can be used as a digital output

Yes it can. Just refer to A0 as pin 14, A1 as pin 15 and so on.

6

Yes it can. Just refer to A0 as pin 14, A1 as pin 15 and so on.

At the same time? If you could force the output to a high or low value and
then measure the voltage drop across the output transistor you would
know if current is flowing.

(* jcl *)

7

At the same time?

No the output stage is not built like that. You have to do some external stuff like a resistor or bridge rectifier.