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Dim yellow LED


Is it just my yellow ZX-LED or do all of these units appears to be pretty dim. The red, blue and green ones all seem to glow bright but the yellow is a real disappointment :(. I’ve tried swapping it into different I/O connectors with the same dim results.


The blue is the brightest for sure and then comes red then green and the least bright is yellow I think…it is still should be bright but not as much as the blue one.


The yellow looks a good bit dimmer and it appears to be visbly flickering.

p.s. I’ve ordered another module from a UK supplier to see if it is the same. Should be here in a day or two. Will report back.


Maybe the LED you have is bad? Try it an a different pin


I’ve already tried it on a different I/O pin with the same “dim” results. See the info in my 1st post in this thread.


See the flickering thing to me would have implied that there was some other signal on the pin that wasn’t doing what you expected, but if you’ve changed your pin and not changed anything else in the program (and I’m assuming you have a simple “flash me” code) then that doesn’t seem to be right.

If you connect to raw power, potentially not off your Fez as well, do you get a different result? LEDs do vary a little, so perhaps yours just needs a different value resistor to get the same intensity - that might unfortunately mean disassembly but since you’re going to try a different one you might not have to revert to that…


Have you tried looking at all of the LEDs in a dark room? I’m wondering if it looks dim as it is getting washed out by the ambient light in the room.


Yes, tried looking at all the LED’s plugged in at the same time in both bright and dark lighting conditions.

I’ll see what the other yellow LED module looks like once it arrives. It is the best next step to evaluate if the module has a problem or not.


Sorry for taking so long to come back to you.It was my bad that was causing the “dim yellow LED”. Nothing wrong with the hardware… only my dodgy understanding of what was in front of me.Thank you for trying to help out earlier.

Here’s the simple code that makes it flash!

public static void Main()
            // Blink board LED

            bool ledState = false;

            OutputPort led = new OutputPort((Cpu.Pin)FEZ_Pin.Digital.IO6, ledState);

            while (true)
                // Sleep for 500 milliseconds

                // toggle LED state
                ledState = !ledState;

Case closed.


Check the current usage.

If its pulling say… 20mA it won’t get any brighter.
You can always change the LED it for a bigger MCD value.

if its only pulling 2 -5 mA then the limiting resistor can be changed.

Sorry about this post I missed the last one ingore if you want…