Very slow PWM dimming over hours

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Systembolaget
 
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Very slow PWM dimming over hours

Post by Systembolaget »

Hej,

for a plant illumination project, I need to dim up and down during the day (simulating morning to evening). Can I use this https://learn.adafruit.com/led-tricks-g ... longer-fix approach? Would I better need another timer IC to advance over the 256 steps at certain time intervals towards noon and then back, or can I time with the Adafruit Metro Mini only?

Is there a way to use 1024 or 4096 quantised steps instead of the 256 in your example, so the dimming up and down periows won't look so "steppy"?

Thanks!

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Re: Very slow PWM dimming over hours

Post by adafruit_support_bill »

You could use the gamma correction, but that effectively lowers the resolution, since some output level are skipped. The AVR processor PWM resolution is just 8 bits. If you want higher resolution, you could use something like the PWM/Servo breakout, or one of the M0 based processors. These have 12 bits of resolution.

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Re: Very slow PWM dimming over hours

Post by Systembolaget »

Ok, thanks; so with the Metro Mini, I have 5 hours dimming up/down in 256 steps and with your ItsyBitsy M0 Express or Trinket M0 I (I need something around the Metro Mini size) could have 4096 steps.

Or I could use Adafruit 12-Channel 16-bit PWM LED Driver and keep the Metro Mini (I'd prefer that) and then dim up/down in 65536 steps.

The three LED drivers MEAN WELL LDD/LDH series I'm using in parallel in this project have a PWM input pin so probably the 16-bit PWM board is the superior option as far as I understand, only needed to generate the PWM signal to the LED drivers (I won't power the LEDs directly from the PWM board, so to speak).

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Re: Very slow PWM dimming over hours

Post by adafruit_support_bill »

My experience with MeanWell drivers is that most expect a 10v control signal. Check your data sheets to be sure.

The 12 channel 16 bit board can handle up to 17v, but is designed for directly driving LEDs via its constant current outputs, so you will need some sort of dummy load.

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Re: Very slow PWM dimming over hours

Post by Systembolaget »

Thanks; all PWM constant current sources from MEAN WELL accept anything between 2.5V - 6V DC on the PWM pin, some accept 2.5V - 10V DC. The "must be 10V myth" seems to originate from flashlight and aquarium forums. I'm using these little PSUs since years without any voltage problem from Trinket Pro and now Metro Mini I/Opins.

What do you mean with "dummy load"? What could I use for that?

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Re: Very slow PWM dimming over hours

Post by adafruit_support_bill »

all PWM constant current sources from MEAN WELL accept anything between 2.5V - 6V DC on the PWM pin, some accept 2.5V - 10V DC.
The MeanWell ELN-60 series datasheet calls for 0-10v or 10v PWM. In my tests, most samples needed at least 7-8v to work reliably.
What do you mean with "dummy load"? What could I use for that?
The constant current output is going to try to deliver 15ma to each channel. Not sure how it will act with a high-impedance load. It might just peg the output which would probably be OK.

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Re: Very slow PWM dimming over hours

Post by Systembolaget »

Ah, the good old ELN series... that's a constant voltage driver of the old "yuuuge brick" type, discontinued in the EU ; )

For contemporary COB LEDs, the LDH, LDB and LDD series are great, go well with any Trinket or Metro where high-quality LEDs are involved. Also very affordable for hobbyists. The drivers from TCI, probably the best in terms of breadth of choice https://win.tcisaronno.com/downloads/?I ... field=docs also in part come with ZIGBEE functionality and many other goodies, such as being able to select constant output current with dip switches over a wide range. Quite many UL-approved little bricks from Italy.

Ok, I just get some Adafruit 12-Channel 16-bit and a few ItsyBitsies (you always have these fun product names... must be a right laugh thinking those up for every new item) and just experiment until the sparks fly.

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