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Thread: DIY PAR meter, Yeah you heard me Reply to Thread
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Topic Review (Newest First)
Today 02:19 PM
mistergreen You will have to ask Lowes & home depot what the specs on those acrylic sheets. They vary.

The code on the CEP is specifically for 1/8" 2447. You're welcome to change the code but you'll need a PAR sensor, or a calibrate CEP to calibrate.
Today 01:54 PM
Quizcat Do you think that a white opaque acrylic sheet from someplace like Lowes or Home Depot would suffice, something they sell as a flat sheet shade material for flourescent light fixtures for example. Those are probably about 1/16" thick.

Would you consider that to be the wrong type of material, and/or too thin?

Quote:
Originally Posted by mistergreen View Post
I found the paint container at Hobby Lobby I think. It might be easier to buy off their online store because you never know what they have in stock at the stores. I'm sure you guys can find another way to build the housing though.

As for the diffuser, it's 1/8" thick 2447 white acrylic. I've only found them online. I've posted the links on the first post.
Today 01:22 PM
mistergreen I found the paint container at Hobby Lobby I think. It might be easier to buy off their online store because you never know what they have in stock at the stores. I'm sure you guys can find another way to build the housing though.

As for the diffuser, it's 1/8" thick 2447 white acrylic. I've only found them online. I've posted the links on the first post.
Today 12:54 PM
Quizcat Mistergreen,

Can you advise where you obtained the jars/lids? I recall from reading early in the thread that you had some difficulty at first finding a jar that did not have an obstructed bottom area where there was an embossed area, printed matter, or an uneven surface area, which would distort the light coming through the bottom of the jar, and that it needed to be perfectly flat to achieve the best results.

Also, can you advise your source, and/or the specifications for, the acrylic diffuser material. Some have PM'd me requesting this information so they can build a sensor to the proper specification. I didn't want to advise them to obtain just any acrylic from Lowes or Home Depot, not knowing if there is a particular scientific standard or charactertistic to the acrylic you used.
05-23-2015 12:31 PM
Quizcat For those of you intending to build one of the CEPs...There are a couple of important things I learned when building the sensor that you might find helpful.

I had done what I thought was a really nice job of encapsulating the entire bottom part of the photo diode, from the side rim of the photo diode, all the way down to where the cable begins, making absolutely certain not to get any caulk on the face of the photo diode, so as to not obscure in any way the area where the light is collected through the photo diode surface.

I thought this would seal everything up really well, but the caulk must have acted as a conductor, causing the leads to short, and readings to be way off on the meter. So, I pulled the caulk loose, and cleaned everything up (once the caulk was dry). Readings came back to normal, and the meter starting working perfectly again. Maybe it's the brand of caulk I used...who knows? I used a caulk made by Locktite that comes out white and dries clear. Perhaps another brand, such as GE Silicone, would not have caused this problem...not sure. If you do caulk the leads, make sure you allow several days for it to dry. Perhaps that would have avoided the issue of the leads shorting. But, after waiting at least two days for the caulk to dry, I still experienced the issue with the short, and the meter returning bogus readings. I also tried caulking where the jar lid meets the jar, on the inside. But, drying time was so lengthy, that I abandoned that idea, and cleaned all the caulk up that was on the inside rim of the jar rim and lid.

I finally decided just to caulk the outside surfaces of the jar rim where it meets the lid, also caulking around where the cable meets the cable connector. I also completely caulked the cable connector where it meets the outside top portion of the jar lid where the cable enters the jar. Actually, I made two applications of caulk, allowing the first application to completely dry before moving on to the second application. It seems to have sealed very well.

So, caulking the leads of the photo diode doesn't really seem to be necessary. But, if you do it, I would recommend caulking each lead separately, and trying not to get any between the leads, allowing it to dry a long time, thereby avoiding potential for a short between the two leads of the photo diode, assuming mine wasn't sufficiently dry after two days. When I soldered the leads, I also used heat shrink on each lead, which I thought would sufficiently insulate the leads from a short by the caulk. But, I suppose that enough caulk migrated from one pin entry point into the diode to the other pin entry point, and created a short.

Also, if you want to layer the Rosco Filters the full diameter of the acrylic diffuser, like I did, this may be of interest. I requested some sample sheets from Rosco Filter Company, requesting a sample of each of the specific types that are outlined earlier in the thread. I requested them in the size 6" x 10", so I would have plenty to work with, since I have several PCBs, and figured I might want to build more at a later date. I never received an answer from them after making my request with their customer service department via email. But, low and behold, a sample of each showed up in the mail today, in the size I requested, 6" x 10", and free of charge.

Also, just so you are aware, the face of the photo diode is pushed all the way flush with the Acrylic Diffuser/Rosco Filter Sandwich on the inside of the jar. I then painted the jar because I figured that mine looked better that way, and I figured it would also limit light entering the jar from the sides/lid of the jar, thereby directing light only through the surface of the diffuser. I doubt that it's functionally necessary to paint the side walls/outside lid of the jar, but it can't hurt.
05-21-2015 03:24 PM
Quizcat That's what I figured too...You wouldn't probably need to use it very often, maybe once every four to six months to make sure everything is still on PAR, and if not, time to buy new bulb(s).

Where I can see using it more frequently at first is in designing a fixture for a tank. I've been working on several fixtures over the last several months, some good, some not so good. Without a PAR meter it has all been guess work. You know, little algae blooms here or there, some plants not responding like you had hoped, etc... I'll still have to guess at it when building another fixture, but the PAR meter will sure help in determining if I'm on the right track.


Quote:
Originally Posted by mistergreen View Post
A 9V battery will last you years. You won't be using the meter all that much. At first, you'll be measuring everything but then it'll go in the drawer
05-21-2015 01:37 PM
mistergreen A 9V battery will last you years. You won't be using the meter all that much. At first, you'll be measuring everything but then it'll go in the drawer
05-21-2015 12:30 AM
Quizcat Great idea engineering that kind of voltage latitude into the design. It's nice to know we can use a power supply (ie: brick) to power the CEP if we want to, and not be particularly concerned about burning it up.

Just curious, do you have any estimate of how long the CEP will last on 9v battery power?

Quote:
Originally Posted by O2surplus View Post
Quizcat-

Don't worry about burning up your CEP due to over-voltage. The regulator that it uses is good for 30V/1amp. I use that regulator all the time in applications where it's fed with 24V, and I've never had a failure. The Reg has built in protection circuits that will prevent it from being damaged, so feel free to feed it with any voltage between 7 & 24V.
I had an idea for a wand...but haven't built it yet. I was thinking of using a 1/2" piece of PVC pipe, in whatever length is convenient for the tank in question, then installing some bends using 45 or 90 degree PVC fittings on the end, then feeding the cable through the pipe so that the sensor is pointed up. Conceptually, I was thinking that there may even be a way of permenently connecting the jar, via the cable connector, to a PVC fitting opening at the end of the wand, to give it more rigidity and permanence, but I haven't checked at the hardward store to see what kind of fittings might be available for that part of it. That cable bushing is about 1/2" diameter after all, and it might be adaptable to fit right into a PVC fitting opening at the end of the wand, oriented the sensor at a right angle to the light source...possibly using an adhesive or caulk of some kind to permanently join the cable bushing to the end of the PVC. That would make the entire thing water proof too, versus the metal coat hanger idea. My only reservation is the height off of the substrate that a PVC wand might require, could be several inches, which would require you to allow for several inches of descrepency in relation to not being at the substrate when reading the PAR meter.

Quote:
Originally Posted by rottison View Post
I can get pics tomorrow but just think of the glass tube being the same size as your pointer finger with the photodiode siting on top.
05-20-2015 11:05 PM
mistergreen
Quote:
Originally Posted by rottison View Post
I can get pics tomorrow but just think of the glass tube being the same size as your pointer finger with the photodiode siting on top.
And it's long? I'd worry it would break.
05-20-2015 09:25 PM
rottison I can get pics tomorrow but just think of the glass tube being the same size as your pointer finger with the photodiode siting on top.
05-20-2015 08:59 PM
mistergreen You'd have to provode pictures. Not sure what you mean.
I have an algae scrapper with a long handle and prongs. I use that to get anything to the bottom of my 75G if I don't feel like getting my arm wet.
05-20-2015 07:55 PM
rottison the glass tube is about half as big again as the photodiode. So there is not a lot of extra room. has anyone put a handle on this? I can't reach the bottom of my tank with out standing on a foot stool
05-20-2015 06:45 PM
mistergreen
Quote:
Originally Posted by rottison View Post
after reading that the shrink wrap didn't work out is due to just not enough surface space at the end for the diode to read from I was planning on putting mine in the bottom of a glass rod about the size of a pencil 12mm with the small piece of white diffuser in front of the diode. does the surface area need to be bigger as in the 1 inch small paint jars ?
Not sure but It definitely needs to be bigger than the photodiode.
05-20-2015 06:00 PM
rottison after reading that the shrink wrap didn't work out is due to just not enough surface space at the end for the diode to read from I was planning on putting mine in the bottom of a glass rod about the size of a pencil 12mm with the small piece of white diffuser in front of the diode. does the surface area need to be bigger as in the 1 inch small paint jars ?
05-20-2015 05:05 PM
O2surplus Quizcat-

Don't worry about burning up your CEP due to over-voltage. The regulator that it uses is good for 30V/1amp. I use that regulator all the time in applications where it's fed with 24V, and I've never had a failure. The Reg has built in protection circuits that will prevent it from being damaged, so feel free to feed it with any voltage between 7 & 24V.
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