Hello,
This is not Raspberry Pi specific but I thought I'd ask here anyway.
I have an MCP23017 chip to control multiple LEDs over serial communication (I2C). I wired it up as per the following diagram:
![Image]()
My problem is that when multiple LEDs are turned on at the same time, the brightness dims slightly.
The blue LEDs dim when one red LED is on, even more when both red are on.
Neither blue nor red seems to dim at all when other blue lights are on.
One red dims a bit when other red is on.
The blue LEDs (and maybe also the red, I can't tell) flicker slightly when all are on.
I'm no expert on electronics, but I'm guessing it has something to do with the resistance of the LEDs and how much current/power they draw. Is there any way I can re-design the circuit to prevent dimming or can it not be avoided?
This is not Raspberry Pi specific but I thought I'd ask here anyway.
I have an MCP23017 chip to control multiple LEDs over serial communication (I2C). I wired it up as per the following diagram:
My problem is that when multiple LEDs are turned on at the same time, the brightness dims slightly.
The blue LEDs dim when one red LED is on, even more when both red are on.
Neither blue nor red seems to dim at all when other blue lights are on.
One red dims a bit when other red is on.
The blue LEDs (and maybe also the red, I can't tell) flicker slightly when all are on.
I'm no expert on electronics, but I'm guessing it has something to do with the resistance of the LEDs and how much current/power they draw. Is there any way I can re-design the circuit to prevent dimming or can it not be avoided?
Statistics: Posted by xtal256 — Tue Sep 23, 2025 1:26 am