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Children Boogie
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Discussion Starter · #1 · (Edited)
*Edit 5-10-13
NOTICE - Firmware has been updated for outdoor lighting.

Final product list:

Photodiode: VTB8441BH
price: $4.660
http://www.alliedelec.com/search/productdetail.aspx?SKU=70219652

Cosine diffuser: 1/8" thickness, 2447 white plexiglass
price: varies, get the sample or buy a big sheet of it.
http://www.eplastics.com/Plastic/Plexiglass_Acrylic_Sheet_Black_and_White
http://www.usplastic.com/catalog/item.aspx?itemid=23681

Basic 16x2 Character LCD - Black on Green 5V
price: $14 but you can get it cheaper on e b a y
http://www.sparkfun.com/products/255

Arduino Uno
price: $30
http://www.sparkfun.com/products/10356
http://www.sparkfun.com/products/11021 (newer model)


Diagram
 

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I made my order in for my DIY peristaltic pump and I bought this guy too

http://www.sparkfun.com/commerce/product_info.php?products_id=9541

cost $1.50

It's sensitive to visible light and a little IR as well so I hope it won't throw the
reading too much. So yeah, it's not super accurate but maybe good enough
for the regular hobbyist.


I've already started building the waterproof body to hold the photo cell. The case
doesn't have a diffusor like a real PAR sensor but hopefully it'll be fine.


It a little plastic paint jar and wires are threaded through the tubing. The signal
will be read with my handy all purpose ardiuno...


Thanks to Hoppy's PAR chart, I can calibrate the signals to a rough guessimate.




Compared to a $300 PAR meter & sensor, this might be a deal.
Neat project, but that is a light sensor not just PAR, so would measure lumens.
 

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The little photodiode might sense PAR or it might sense nearer to lumens, or anything in between. Considering the cost, that slight disadvantage isn't that important. It could work well for adjusting the height of T5 lighting, checking how much shading the plants are doing, noting bulb deterioration, etc. But, for getting data that can be compared to other's data, it wouldn't be that great.
 

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Children Boogie
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Discussion Starter · #4 ·
Good point.

I think taking the average of all of the readings per second would make it PAR?
All of the math can be done through my microprocessor.
 

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Children Boogie
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Discussion Starter · #6 ·
No need to send me a PAR meter although I wouldn't mind having one for a while :D

Once it's built I can post some standard readings like sunlight at noon and people with a real meter can confirm the readings.
 

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Different light sources have different spectral output characteristics. I think to make this work you'd need to put a filter which combined with the silicon sensor response would approximate a PAR curve.

Sounds like an interesting project.

Good luck!

jim
 

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Children Boogie
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Discussion Starter · #11 ·
Is there a gel that blocks InfraRed?

Well, hopefully, calibrating the output based on Hoppy's chart might be 'goodnuf'.

I went ahead and contacted Hamamatsu on how to get their photodiode.
 

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If you're measuring underwater I don't think you'll need to worry about infrared. In a dry tank you probably need something but I'd try the green gel first before working on the infrared part. In an otherwise subdued light room you'd be measuring the output of flourescents which don't have any significant IR output to measure. If you're measuring incandescent or MH that's a completely different story with lots of heat output.

Good luck!

Jim
 

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mistergreen, what's the difference between relative spectral sensitivity and photo sensitivity? If they're the same, the trend of the graph looks similar however, the peaks are very far off(1.0 and 0.3). If there is a scaling factor/calibration, it would be worth looking into before spending $17 bucks.

Sorry if my questions/comments sounds dumb, I am no light expert, just want to contribute and point out what I though to be a little bit of inconsistency. Overall, I think you have got brilliant idea rolling!

Edit: I looked at it again and seems like the photo sensitivity/peak of photo sensitivity = relative spectral sensitivity. Is this correct? If it is, it may fit pretty well.
 

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Children Boogie
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Discussion Starter · #14 ·
Oh, I'm just looking into the Hamamatsu diode... Haven't bought it yet until I played around with the cheaper diode.

photo sensitivity is a electrical engineering term referring to photodiodes:
http://en.wikipedia.org/wiki/Photosensitivity#Interpretation_in_electronic_engineering

And spectral sensitive is another term for photo sensitivity ( another unit of measurement like inches & centimeters ).. I assume they measure the same thing.
 

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Children Boogie
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Discussion Starter · #15 ·
I received the photodiode yesterday. Got to play with it a little. In this picture, I'm trying to find the right resistor for this set up.


A 4.6K resistor seems to work. I'm calibrating the max output to sunlight.. 1024 (5V) is the max reading and sunlight through a window gives a reading of ~900. So I think I got it.

Mounted the photodiode on a electrical cap


Assembled the jar... This nub in the jar is a problem. It casts a shadow on the photodiode.


I moved the diode to the side and gave the plastic a little frost with fine grit sandpaper to scatter the light a little.



Next step is to calibrate these numbers to the PAR readings.
 

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Truly some pioneering DIY action! Great job!
 

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Children Boogie
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Discussion Starter · #18 ·
I don't think I showed you how I'm reading the values so far.



It's all through USB... It's supplying the ardiuno power and a way for the ardiuno to communicate to my computer...
This is my serial monitor outputting the values.


The values jump/dance around like it's being hit by photons, kinda cool. So I wrote the code to find the average within every second...

NON-PAR code...(NOT FINAL)
Code:
unsigned long average = 0;
unsigned long time;
int counter = 0;

void setup() {
  Serial.begin(9600);
  time = millis();
}

void loop() {
  int sensorValue = analogRead(0);
  average += sensorValue;
  counter++;

  //every second or 1000 millis
  if(millis() > time+1000) {
    average = average/counter;
    Serial.println(average);
    
    //reset timer & counter to get ready for the next second.
    time = millis();
    counter = 0;
    average = 0;
  }
}
Oh, I double checked the readings by going outside... Full sun will give me the maximum value of 1023.. In the shade, around 100-120.
 

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I think PAR in full sun at midday is around 2000. That suggests your readings may be about half of the true PAR values.
 
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