CFA-635 LED swapout - uC loading OK?


New member

I'd like to change the four red/green LEDs on my CFA-635 for red/blue types. This is useful because the green LEDs are exactly the colour that gives problems to people with red/green colour sight issues; my father, for instance, is unable to tell the difference without having one of each to compare to.

I have found a supplier on Ebay offering 3mm red/blue LEDs, which appear to be pin compatible with those used on the CFA-635. I'm happy to do the changeout and accept responsibility for breaking the thing, but the question is to ensure that I can drive the blue die and that I won't damage the uC. I assume the blue die will have a higher voltage requirement than the green one would have.

It looks to me as if the LED drive strength is controlled by the eight resistors clustered around them, R21-R28; does the uC just drive 5V to these resistors and let them sort it out?

Thanks for any info,

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CF Tech

> does the uC just drive 5V to these resistors and let them sort it out?


I think the port pins on the PSoC are good for 10mA, you can check the Cy8C27543-24AXI at to be sure.


New member
I'm assuming here that 151 means 150 ohms.

High Output LevelVdd - 1.0––VIOH = 10 mA, Vdd = 4.75 to 5.25V (8 total loads
4 on even port pins (for example, P0[2], P1[4]),
4 on odd port pins (for example, P0[3], P1[5])).
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