multiple led outputs

[LPG]

I am making a project where I have a picaxe 08 driving 4 leds. They are not all on at the same time ( they are on different output pins ). I am wondering if four separate resistors are needed - one for each LED, or if I can have them al run through a single resistor to 0v?

 

[eclectic]

@LPG

If you have a minor programming error,
and more than one output is high,
there will be problems.

See post #8 here:
http://www.picaxeforum.co.uk/showthread.php?t=10595&highlight=LED+parallel+resistor

Much safer to use example 2,
with a SIL network.

e

 

[MBrej]

If the LEDs are the same, and only one is ever on at a time, then you can use one resistor, as the resistor will be the same for all LEDs. If you do turn more than one LED on, the LEDs will just be not as bright, and as they are the same, you wont get any problems as described in the above link.

Matt

 

[hippy]

I used one resistor on the common cathode of a 7-Seg LED display because I didn't want to put eight resistors in each of the anode lines. It worked as MBrej described; the more segments / LED's lit the dimmer they all become, but no problems other than that.

As I was using that as a primitive direction indicator and only one or two LED's on at a time it was not a problem.

The noticeable dimming can sometimes be reduced by using a lower value of R as at a certain point bright LED's don't seem any brighter as R is lowered, but don't go below 220R ( or whatever limits to max allowed current through the PICAXE (25mA) or the LED )..

 

[LPG]

Thanks. For this project it does matter whether they are the same brightness. I have chosen to use a separate resistor for each LED.