I'm using a Pic16F684, Quite a small little best.
I'm running on batteries with a low drop out reg of as low a voltage as I can. I'm powering LED's that use 2 volts +- 0.2 volts. When I sink the LED's with a I/O how much voltage does the I/O use.
So I can get some control of the 20 ma into the LED and I/O
I would like to control current +- 3 ma with all the tolerances
and hope to run on 3 volts with some reasonable battery drop off
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Using R = (3-2)/0.003 you come up with resistor value of 333 ohms, so use nearest available value like 330 ohm. Thats if you want to run them at 3ma, if not, then adjust accordingly.
They make little 3mm "low current" leds, and they don't look too bad at 2ma.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I'm using a Pic16F684, Quite a small little best.
I'm running on batteries with a low drop out reg of as low a voltage as I can. I'm powering LED's that use 2 volts +- 0.2 volts. When I sink the LED's with a I/O how much voltage does the I/O use.
So I can get some control of the 20 ma into the LED and I/O
I would like to control current +- 3 ma with all the tolerances
and hope to run on 3 volts with some reasonable battery drop off
Using R = (3-2)/0.003 you come up with resistor value of 333 ohms, so use nearest available value like 330 ohm. Thats if you want to run them at 3ma, if not, then adjust accordingly.
They make little 3mm "low current" leds, and they don't look too bad at 2ma.