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DIY PAR meter, Yeah you heard me

300K views 740 replies 110 participants last post by  henrybri 
#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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#324 ·
My new PAR Meter PCB's arrived yesterday along with more parts from DigiKey, so needless to say- I'm ready to build another batch. One of the PCB's that came in is an Arduino shield that I designed to allow me to burn boot loaders and program blank Atmega 328P-au micro-controllers directly from my Duemilanove. The burning process is fully automatic and doesn't ever require a computer. I managed to assemble one and burn 25 chips last night!The shield is set up to accept chips in the DIP28 and DIP32 package and has a FIT1 input for burning the main sketch. I have a few of these shields left over and will share them with anyone interested in having one.
Here's a photo of the Programming shield/TQFP adapter on top of my Duemilanove.


 
#326 ·
Hey Thanks! I'll send you an assembled one with the next batch. All you'll have to add is a ZIF adapter or a TQFP adapter like mine- and you'll be ready to go.
 
#327 ·
I'm not above bribery :)
Are there any other components that are in short supply I could provide in exchange for a spot on the waiting list? I was going to throw in some cat5 but you've got that covered. I'm not arduino-gifted but I bake a mean oatmeal cookie and my brownies are pretty good.
 
#329 ·


I used these when I was still a test tech at an assembly house programing embedded firmware in various products for customers.
 
#334 · (Edited)
Here's an idea- Why not sandwich the diode between two layers of plastic. You could use two different colors so people would know the "blue side" faces the light source and make them about 2"x2" so they would lay flat on their own. You could water proof the sensor by sealing the two halves of the "sandwich" with aquarium safe epoxy. Whatcha think?
 
#336 ·
I think the heatshrink method should work fine, but I recommend upgrading to adhesive lined heatshrink, it's a thick walled polyolefin but lined with some hot melt adhesive, stuff sticks to almost anything extremely well. It should stick to that acrylic diffuser as long as you get it nice and hot. Remember, silicone doesn't bond well to acrylic.
 
#338 ·
Another issue - unless the silicone is spec'd for electrical use it can be corrosive when used as a potting compound.

I'll have draw up a picture of how I would construct the sensor. I'm just looking for a sure fire way to provide a long lasting= water proof seal for the sensor, that's easy to construct. Drying time for the epoxy would not be an issue since you could pre=solder all the diodes to the wiring, prior to encapsulating all the sensors in 1 final step.
 
#339 ·
I believe GE RTV silicone works with electronics/electrical parts. We used it in the Navy sealing up the mag amp boxes on the flight deck.
 
#342 ·
Cool design but it might take a bit of time to assemble. Plus, I'm worried about the wires coming out of the sandwich. There's no support and can easily break. We can give it support but then it complicates things more.

Fixing it would be impossible as well. You'd have to throw away the whole unit.
 
#345 ·
Be careful with the shrink tubing. While it's a good insulator it;s not very durable and the properties change once its been heated. If you decide to pot the sensor in epoxy you can supply strain relief with short pieces of tubing over the wires just make sure the back ends are surrounded by the epoxy so the water doesn't wick into the wires. You can get epoxies that will adhere to Acrylics and polycarbonates. Try Loctite Epoxy plastic bonder it looks like it may work.
 
#349 ·
just got the meter today :D and ofcourse tried it right the way. but have one question, how should i hold the sensor ? if i hold it bottom up the readings are way to high for my light so looks like horizontal position is way to go. it gives more sensible readings. any tips?
 
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