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High photosynthetic photon flux density (PPFD) and LED dimming (pulse width modulation)

zozo said:
I can not fully explain PWM away and i think the explanation as an On/Off pulse is a bit too straight forward and simplified theory. It is also used to control the speed of electrical motors. And even a simple voltmeter is kinda fooled by it. I hooked a simple digital voltmeter to the PWM controller and it shows +/- 6 volts if it is turned down to 50% output. But in theory, it should stay 12 volts at different on/off frequencies.
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Couple of points
1) Most meters will end up "averaging" so your 6V at 50% is expected..
12V 50% + 0V 50% averages to 6V 12/2 periods so to speak.
2)There is some rise/fall time but usually not important.
Sort of like this:
Blue is the signal.. yellow is the current. Just a rough example but you get the idea.
AMC7135-PWM-frequency-1.gif
LED's do "quench" fairly instantaneous, unlike things like incandescent bulbs.
May be some phosphor lag w/ whites or other phosphor converted diodes ("lime" or like the cheap "full spectrum" diodes (magenta looking ones w/ red phosphors and a blue pump)

4) motor/fan speed PWM control usually uses much larger pulse frequencies like 2 kHz up to about 10 kHz. (rough estimate)
Most LED controllers use like 500Hz.
Point is frequency needs to be part of the discussion.

5) Consider livestock
6) there is natural PWM such as leaves blowing, clouds though obviously not exactly KHz ranges.
 
https://cdn.intechopen.com/pdfs/60304.pdf
5. Conclusions: Pulsed light at high frequencies (2–20 kHz, 50% duty ratio, 200μmol m2s1) positively affected the growth of lettuce leaves under controlled environment. The photosynthetic performances showed differences between leaves developed under pulsed light and leaves developed under continuous light, when the CO2 uptake rates and chlorophyll fluorescence parameters were measured at lower frequencies (<2 Hz). In the pulsed light technique, it is important to determine both optimal frequency and duty ratio for plants to attain the mostefficient use of harvested light. The reason why growth was enhanced under pulsed light athigh frequencies has not been resolved by analyzing photosynthetic performances in this study.
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Keep in mind some things are species/cultivar specific.
 
Would be a fascinating thing to study. pHD opportunity awaits someone. Maybe start with POT plants as people are intensely interested in them....( DUUUUDES 🙂 )

:cigar:
 
I'm way ahead of you - I've just purchase an incredibly high wattage LED. To be honest, I cannot afford a good enough dimmer, PAR meter or the oscilloscope thingy, so any hard evince will be a while yet. I also need a deeeeeep tank. 😀 So expect to hear more on this. It's going to be citizen science at its zenith, if I don't go broke, mad, drown, or more likely blind in the process. I'm going to do a terrestrial dry run :hilarious: first. They actually call this a "pot study/trial" in science literature.
 
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@Simon Cole dude we are on your side. 😉

TC420 can handle a bit of PWM dimming. There are some small oscilloscopes which might be enough but they are around $200 or so.

Good luck to your wallet.
 
rebel said:
@Simon Cole dude we are on your side. 😉

TC420 can handle a bit of PWM dimming. There are some small oscilloscopes which might be enough but they are around $200 or so.

Good luck to your wallet.
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You can actually use the DAC in your computers soundcard .. 😉
For external sources care has to be taken, not to exceed the voltage range of the inputs. The range is usually only ±0.7V !! If higher voltage need to be analyzed, a voltage divider has to be used. Additional protection diodes are recommended in order to avoid any damage to the sound card and to the computer.
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.
https://www.zeitnitz.eu/scope_en
I briefly tried some software (Zelscope???) ..
Aduino based "Typhon" (a DIY project turned commercial in the US, now StevesLED "hurricane" controller (upgraded version) ) controller 5v pwm output.
10pwmat60pc.JPG
I am not responsible for people burning out soundcards or any computer issues.. JUST a suggestion..
I'm sure it has a bunch of limitations..
I do not remember if I limited the voltage in any manner. Do not believe I did though and the card survived the "5V".
Only played with it briefly.
 
I think I'm on 0-10V dimming. The chips will be regulated but the unit is 240V. Good idea though @rebel . I'd probably run comparisons against a series of quartiles, at points in height when we know light intensity should result in photosynthesis inhibition. Obviously light through water at depth does funny things. But if the problem could be solved - boy what fun. We could have a light on a moving boom that goes over shallow plants at a wide PWM, into deep water carpets at zero PWM - all with one high intensity light at one set height, just with a single programmable dimming switch, and a moving boom. We could have planted carpets at 3 metres depth in indoor swimming pools and still grow stem plants around the margins. It would be like ADA mark II.
 
oreo57 said:
I am not responsible for people burning out soundcards or any computer issues.. JUST a suggestion..
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Dude I didn't know my computa had a sound card???? I used to use sound blaster cards on my PC but these days seem to be built in....
 
Sound chip eh.... It must be part of the mother board in that case! What an interesting idea to use it to monitor wave forms!
 
rebel said:
Sound chip eh.... It must be part of the mother board in that case! What an interesting idea to use it to monitor wave forms!
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It has limitations...
Bandwidth
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, or how wide a frequency range they can measure effectively. The lab-grade scope in this case has a 200MHz bandwidth, meaning it can measure from 0 to 200MHz very well. The bandwidth of the sound card is much lower: about 20 – 15kHz. Anywhere out of this range and measurements get sloppy.

Sample Rate The lab model here has a sample rate of 2GS/s! The sound card in your computer is only around 44kS/s. So, you see why faster waveforms may not be captured as well. In essence, the sample rate is how often the system measures the voltage. So, a lab model can measure up to 2 billion times per second while the sound card model does it 44 thousand times. You may think this really negates the use of this DIY tool. Not so! In many hobbyist circuits 14kS/s is more than fast enough to measure your pulse widths and frequencies.
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https://makezine.com/projects/sound-card-oscilloscope/
 
Hi Guys,

Just thought I should mention the following:

https://www.picotech.com/data-logger/drdaq/overview

You will see that it can be used as a 100kHz bandwidth 'scope. Generally-speaking, pico Technology produces some good stuff. I have many times considered getting one of these little boards and it may still happen. My hands-on electronics knowledge is now pretty rusty. But, I once built an oscilloscope with CRT and that was 50 years ago! Everything was discrete in those days. ICs were just beginning to appear on the market!

JPC
 
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