[sdiy] LED current source needed for 'digital' outputs?

Justin Owen juzowen at gmail.com
Sat Mar 1 14:20:35 CET 2014


>> For an LED displaying a simple on/off digital signal - e.g. a logic output - is there any reason to not just use: Source > LED > R > GND?
 
From: Gordon JC Pearce [gordonjcp at gjcp.net]

> Most digital outputs pull down rather better than they pull up, so you'd be better to wire it between +5 and the pin.  Put a 150 ohm resistor in series (or really anything you have within about 100-470 ohm, it's not at all critical) and you'll be fine.

From: Tom Wiltshire [tom at electricdruid.net]

> That's why you sometimes see LEDs hanging off the +5V rail and giving an inverted output.

Inverting and hanging them off a Vref is great idea - thanks guys.

- J




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