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Joined: Fri Oct 19, 2018 6:59 pm

Direct feedback loop and light intensity control: diurnal cycle.

Fri Oct 19, 2018 9:02 pm

Big picture: RPi, PWM, dimmable LED driver, and feedback circuit to mimic sunrise through sunset.

So we've been working with some orchid and moss species for some bio-geochemical projects. The current environmental chamber I'm using I built from scratch. The lighting situation is as follows:

10 x Cree XM-L2 U2-bin emitters
- Vf at 1000 mA = 2.9 V
- Vf at Imax (3000 mA) = 3.3 V

Driver: 2 x Meanwell LDD-1000. One driver for every 5 emitters.
- maxes out at 1000 mA, other models are available that go a bit stronger, but I really don't need any brighter at the moment. I'm happy with one amp being "high noon on a sunny day" in the chamber.
- PWM dimming

Power is a simple Meanwell line AC to 24 V bench top switching supply.

I'm asking for the RPi BB's help designing a basic feedback control to:
1. measure light intensity,
2. make a comparison with a set point. The set point changes every hour during the day to reflect the diurnal cycle of intensity.
3. adjust the PWM signal accordingly,
4. repeat.

I have a RPi zero W and a 3 B+, but I would rather use the zero W.

I'd be thrilled with even fundamental suggestions, what type of photodetector to use, what type of feedback circuit would work, etc. etc.

Much much gratitude.

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