DIY PAR Meter - Page 2 - The Planted Tank Forum
Reply
 
LinkBack Thread Tools Display Modes
post #16 of 60 (permalink) Old 03-05-2014, 06:11 AM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
Quote:
Originally Posted by Jalopy View Post
Looks awesome, are you going to print it?
I haven't decided, yet. First, this design needs the dome part to be somewhat translucent, so it acts as a diffuser, and I'm not sure what material will do that. Second, I don't know who to have do it, and if I can afford it. I'm really tempted though. I think I still have one of the photodiodes to use in it, but I'm pretty sure I'm out of the filters needed to make it work right. Last, I'm not sure that this is an optimum design yet.

Hoppy
Hoppy is online now  
Sponsored Links
Advertisement
 
post #17 of 60 (permalink) Old 03-05-2014, 07:11 AM Thread Starter
Planted Tank Obsessed
 
Join Date: Aug 2013
Location: SF Bay
Posts: 468
I think I have some Roscoe filter from one of your earlier designs. For the dome, I suggest the frosted or translucent acrylic material from Shapeways. You might have to print a dome in each of the materials to test it out.

The design looks good overall though.

Jalopy is offline  
post #18 of 60 (permalink) Old 03-05-2014, 04:56 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
Quote:
Originally Posted by Jalopy View Post
I think I have some Roscoe filter from one of your earlier designs. For the dome, I suggest the frosted or translucent acrylic material from Shapeways. You might have to print a dome in each of the materials to test it out.

The design looks good overall though.
Shapeways looks interesting, and their "frosted" material looks ideal for a diffuser. I will be studying this more today to see if I want to proceed to a prototype or prototypes. If I do this I also want to do more work selecting the filter(s) to shape the spectral response to be at least as good as the Apogee Quantum meter response.

Since this is hobby activity for me, the more work I have to do, the more fun it is!

Hoppy
Hoppy is online now  
post #19 of 60 (permalink) Old 03-05-2014, 10:09 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
I just ordered one of each of the two parts, black acrylic for the body and white frosted acrylic for the dome. First, I added the hole for the electric cable in the body, saving the work of drilling the hole, and the risk of breaking it while drilling it. I learned the hard way that you have to be sure to specify that the drawing is in inches, not mm, when you order the parts! (Or do the drawing in mm.)

The cost is about $31 with shipping included. If I had ordered 10 the shipping cost would have been a lot less, per unit. Even so, the sensor is going to cost around $30 for parts only.

Hoppy
Hoppy is online now  
post #20 of 60 (permalink) Old 03-07-2014, 02:50 AM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
About 2 years ago I began looking for a combination of Roscolux filters that would change the spectral response of an Excelitas photodiode to equal that of the Apogee Quantum PAR meter. I found many combinations that were usable, but until today I never found a combination that almost exactly duplicated the Apogee response. Here is that Apogee spectral response that is the goal:

The colored area is the ideal PAR meter response, the definition of PAR being all of the radiation between 400 and 700 nm wave length.

An Excelitas VTB8441BH photodiode has built in filters to give this spectral response:


Today I found a 3 filter combination that works very well, using the spectrum plots shown on the Rosco website, http://www.rosco.com/filters/roscolux.cfm Here is how I calculated the response:


These are the three filters, along with their transmission at each of 20 wavelengths. I used a spreadsheet to figure out the sensitivity of the diode at each wave length by multiplying the transmission percentages at each wave length together and multiplying that by the relative sensitivity of the diode at those wave lengths. Then to be able to plot that on a graph I converted each of those sensitivities so the the highest one is 1.0 and the others are fractions of 1.0.


When this is plotted on a graph, along with the Apogee Quantum PAR meter spectral sensitivity it looks like this:


You can see that a PAR meter using that photodiode and those filters would cover the whole PAR range better than the Apogee meter, but at the cost of including a little of the radiation outside the PAR range. I think that is a good trade off.

If the 3D printed parts here work out right, and if it is possible to adjust the assembly to calibrate it to read PAR accurately with just geometry changes, this should make a very good PAR meter.

Hoppy
Hoppy is online now  
post #21 of 60 (permalink) Old 03-07-2014, 07:48 AM Thread Starter
Planted Tank Obsessed
 
Join Date: Aug 2013
Location: SF Bay
Posts: 468
Looking good. You need to post some data when you're done.

Jalopy is offline  
post #22 of 60 (permalink) Old 03-08-2014, 02:33 AM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
I just received a package of two of the LX1010B lux meters, which I didn't order, and with no indication of where they came from. Does anyone know anything about this???? If it is an anonymous donation to this project I really appreciate it.

Hoppy
Hoppy is online now  
post #23 of 60 (permalink) Old 03-08-2014, 08:49 AM Thread Starter
Planted Tank Obsessed
 
Join Date: Aug 2013
Location: SF Bay
Posts: 468
That's pretty awesome but it wasn't me. Put them to good use!

Sent from my DROID RAZR using Tapatalk

Jalopy is offline  
post #24 of 60 (permalink) Old 03-08-2014, 02:53 PM
Algae Grower
 
Join Date: Sep 2013
Location: Melbourne, FL
Posts: 11
Gentlemen,
Have you looked into what is available in smart phone. I have a Galaxy S4 and an app, Galaxy S4 Sensors, that has a Lux meter in it. I think it uses the front camera as the sensor.

I have on of Hoppy's DIY Lux meter and will try it as soon as I can find it.

Of course, I worry about putting a $600 smart phone under water.

Joe

Repairing 120XH, building a LED light
JoeFL77 is offline  
post #25 of 60 (permalink) Old 03-08-2014, 04:00 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
Quote:
Originally Posted by Jalopy View Post
That's pretty awesome but it wasn't me. Put them to good use!

Sent from my DROID RAZR using Tapatalk
As I recall I saw a falling star last week and made a couple of wishes before it vanished: world peace and a couple of lux meters. Win some, lose some!

Hoppy
Hoppy is online now  
post #26 of 60 (permalink) Old 03-17-2014, 11:25 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
The prototypes of the two sensor parts I'm having made have been shipped today, so I should have them by the end of the week. This is a slow process compared to making things yourself.

Hoppy
Hoppy is online now  
post #27 of 60 (permalink) Old 03-24-2014, 10:22 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957


The parts arrived today. The translucent dome seems to pass more light than I expected, and the fit isn't what I expected, so I will have to do a little sanding to get the dome to fit over the body part. Other than that they look very good, and should work fine.

Now I just need to assemble this, and experiment to see how I can alter the design to make it always work without laborious testing, adjusting, re-testing, etc. Ultimately, I hope it will be possible to make this work with a single 3D printed part, so the cost is much less.

Hoppy
Hoppy is online now  
post #28 of 60 (permalink) Old 03-25-2014, 10:18 PM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957


It works, but is far too sensitive to be usable as it is now. It reads about 3500 when the PAR is about 41, so on the 50,000 scale it reads a little low, and on the 20000 and 2000 scales it reads way too high. Adjusting the height of the translucent dome above the diode works for about a +/-5% adjustment, which is good, but the overall sensitivity is just too high. It sure looks good though!

The three fixes for this would be making the dome from white acrylic instead of translucent acrylic, or making it much thicker above the diode, from ,050 inch to perhaps .50 inches, which is impractical, or making the dome much higher so it is much farther from the diode. I think the best approach will be using white acrylic, which is still a bit translucent. This material just transmits too much of the light.

I think I will try a different design for the next iteration, and use white acrylic for it. The design I'm thinking of is much closer to Jalopy's original design, but a one piece design.

Hoppy
Hoppy is online now  
post #29 of 60 (permalink) Old 03-25-2014, 11:43 PM
No more Bow ties
 
mistergreen's Avatar
 
Join Date: Dec 2006
Location: Cincinnati
Posts: 15,794
Heh, It does look good. That's the material of the diffuser?
I'm assuming the diffuser (acrylic 2447) you used before this one works pretty well.
mistergreen is online now  
post #30 of 60 (permalink) Old 03-26-2014, 04:49 AM
Planted Tank Guru
 
Hoppy's Avatar
 
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 19,957
Quote:
Originally Posted by mistergreen View Post
Heh, It does look good. That's the material of the diffuser?
I'm assuming the diffuser (acrylic 2447) you used before this one works pretty well.
The diffuser dome is made of a translucent acrylic that Shapeways uses. It will never reduce the intensity of the light striking the diode enough - just too transparent. The one I just ordered will be made of white acrylic, which may end up being too opaque, but I like this design better, and it "only costs" me $18 for one, with over half of that the shipping cost. This will be a one piece body, with the walls, other than right over the diode, thick enough to block most of the light. But, only trial and error will work to find a final design.

The acrylic I was using before, for diffusers, is the "frosted acrylic" rod from Tap Plastics. It works very well, but has to be cut with more precision than I can apply, in order to make the sensors reproducible without lots of adjusting and testing - very labor intensive.

Hoppy
Hoppy is online now  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome