• We recently switched our forum platform. If you experience any issues please email support@crystalfontz.com

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,

Looking for additional LCD resources? Check out our LCD blog for the latest developments in LCD technology.

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 http://www.cypress.com 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])).
Last edited:
USB LCD Displays - Graphic and Character LCDs with a Keypad