My Instrumentation and Control System

No worries about the questions… ask away and I will do my best to answer them.

On my setup the LED lights are not dimmable so I regulate lighting with hanging height. That makes the use of a relay switch simple to control them… just on/off

This module costs about 10 bucks and has 8 relay channels:

If your lights are dimmable then that adds complexity to it. I understand most if not all LEDs are dimmed using PWM (pulse width modulation) so the current/voltage stay constant but is switched on/off very fast every second to create a duty cycle.

If the duty cycle is 50% (half output) the current might be on for a total of 1/2 second out of the total 1 second cycle. 25% will be 1/4 second… but it happens many, many times per second so you don’t get flicker.

The only way I see you can do this is get into your lighting control and see what is controlling the dimming, could be just a simple resistor function like a potentiometer.

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Heck, you could maybe even use a servo that is connected to the knob on your dimmer. your control would move the servo in steps to simulate you turning it by hand.

These are used on radio controlled models (cars/planes) and are simple to control with your MCU:

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I can’t lie after I asked I dove I. Some more and found this.

Dope servos! I could use those for work

I looked at the arduino link, and it does appear they are just varying the voltage to the little LED. The analog output from the board steps the voltage from 0 to 5v in 255 steps. Of course your lights are 120v and pull lots of current (watts) so this would only work as a pilot control for a much larger circuit directly handling the lighting load. At some point I would like to upgrade my lights so I am going to be faced with this same problem.

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True didn’t think that thru

I like Adafruit’s line of sensors. That is a nice digital potentiometer. And the I2C communication protocol is a breeze to use. Only thing is each device on the I2C bus has to have a unique address and a lot of sensors has a fixed address or maybe a choice of 3 different addresses.

Adrafuit’s TCA9548A I2C Multiplexer will allow you to use 8 sensors even if they have the same address.

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Thank you for the advice!

This is really cool. I assume you had to make that software too? Thanks for sharing, I am nerding out over here, probably going to cost me a lot of time!

Regarding DLI, a bright sunny day outside will have a DLI of 60, and I see your software gauge tops out at 30. I think somewhere around 40 is ideal for this plant indoors, but don’t quote my dumbass on that, I heard it from a crop physiologist professor video that I can’t find right now. I just remember the reference precisely: 1,000 μmol / m² · s = 43.2 DLI

Thanks again for sharing, truly awesome work!

Hey Chronic,

This is the first grow I have tracked the DLI on, so to be honest didn’t completely understand it so did a lil research to make it more clear. See if this makes sense to you, bear with me while I beat up on it:

DLI (Daily Light Integral) is measured in mol/m2/day

Of course daily is our 24 hrs, light is PPFD in micromoles per square meter per second. and Integral is a calculus term. The reason integration is used is because outside the PPFD is not constant throughout the day and vary due to cloud cover, atmosphere, things like that.

Fortunately, inside our lighting is constant so we don’t need integration, but this is how it could be calculated:

So the equation to calculate DLI is:

DLI = PPFD (micro-moles per square meter every second) x (3600 x photoperiod) / 1,000,000

The 3600 converts seconds to hours 60 seconds x 60 minutes
Photoperiod is the duration in hours the lights are on in hours
1,000,000 converts micro-moles to moles

Sorry about all the math, it is a good thing our plants grow just find without it.

Here is chart one found:

I am still in the seedling stage so working the math I get this
DLI = 300 (ppfd) x 3600 x 18hrs / 1,000,000 = 19.4

When I switch to flowering I will be more like this:
DLI = 1,000(ppfd) x 3600 x 12hrs / 1,000,000 = 43.4

So you are absolutely correct on what you quoted, and yes I need to bump the top of my scale up to maybe 50 or 60.

Good catch on that!



I wish I knew someone with a larger scale operation that had one of those Apogee quantum sensors to let me borrow! This stuff is fascinating.

Me too! I would love to dial in my LUX meter with a true PAR meter.