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Unread 05-03-2011, 09:42
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Re: LEDs on Operator Console?

If you look at the pinout there are actually 4 high current outputs but 2 (P2_3 P2_5) are not used in the default code for the Cypress. If you are comfortable reprogramming the Cypress you could probably get them working. If you don't want to reprogram and you have a few extra NPN BJTs you could drive the base of the transistor with any digital output.

I think we used the 25mA high current outputs for a couple LEDS last year so it can work (provided you wire it correctly as a current sink). The 200 ohm resistor sounds a bit high if you went them bright. If your LEDs are like this Radioshack one the voltage drop is around 2.25v (you could test it with a good multimeter). Assuming you want 20mA I get 52.5 ohms, so use a 56 ohms or higher resistor (higher is always safer).
Math:
3.3 V - 2.25V = 1.05V (to drop across resistor)
V/I = R
1.05 V / .020 A = 52.5 ohms
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