Stabilizing VIN for LEDs

  • I use a strip of 12V LEDs as lighting for my printer. I connect it to Duet's VIN, and everything worked fine until I started using the new auto-tuned heating for my heatbed. The LEDs now flicker obnoxiously when the bed heater is on. Actually, it looks fine at first and starts flickering only once the bed reaches the target temperature. I'm guessing the voltage drops and rises when current draw changes as the bed heater is switched on and off to maintain temperature.

    Can I smooth out the voltage with a capacitor or something? If so, what value would be suitable? My bed heater is 120W.

  • administrators

    Some suggestions:

    1. Switch the bed back to bang-bang control, using the B1 parameter in the M307 command.

    2. Try connecting the LED strip directly to your power supply instead of to VIN. That avoids the resistance of the leads from the PSU to the Duet causing voltage drop at the Duet when the bed heater turns on.

    3. Use a better-regulated power supply (probably in conjunction with (2) above).

    4. If your 12V PSU has sufficient extra power capacity. turn up its voltage to 14V, then use a 12V low dropout regulator to provide a better-regulated 12V supply for the LEDs.

    5. Use a separate PSU for the LEDs, or a separate PSU for the bed heater.

    6. In a future firmware revision I may make the bed heater PWM configurable, then you will be able to turn it up to 70Hz or greater, high enough for the eye not to see.

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