**Project: Photometer kit **
Design : 1.0 version
Zachary Marlow OPEN source
A photometer measures the intensity of a light and the can be used to determine the amount of light being blocked by the sample. The amount of light can help determine suspended solids and the quality of the water sample
In my design the photometer is mostly 3d printed and has a total of four 3d printed parts. There is also the light source (modified laser pointer), GA1A1S202WP sensor (adafruit), Arduino Nano . There is a small area where a custom filter can be added if wanted. The entire device can fit completely in one hand.
Size
Total size : 80 mm x 30 mm
Cuvette
The Cuvettes sold by Pubic Labs works perfect for this application and very affordable.
**Light Source **
In my design, I wanted to keep the overall price down, to allow for this to happen the light source needed to be creative. Dollar General sells a laser pointer for $3, by removing the lens you essentially convert the laser into a red diode.
Method of running the Photometer
Connect the Arduino Nano to your computer and launch the code provided using the Arduino Compiler, once successfully uploaded launch Arduino Serial Graph. Insert a control sample into the photometer to get a base level, copy and paste this data into excel or google docs. Now insert the test sample and repeat these steps for each sample you want to test.
To determine loss:
Sample = S, C= Control, R = Remainder
S/C=R-1
R-1= Loss
Proof of concept test:
Control: Distilled Water
Sample 1: 1/3 Coffee Grounds 2/3 Water
Sample 2: 2/3 Coffee Grounds 1/3 Water
In this test, I created two different samples each with different amounts of coffee in them. I went one by one starting with the control of course just to create a base line on the amount of light. Next went sample one and then sample 2, I copy and pasted each data into google docs and created this chart.
From this data, it can be determined that Sample 1 blocked a total of 14.51 %~ of the light and Sample 2 blocked 18.32%~ of the light.
Coding the Arduino:
Now in this project there is a little bit of coding necessary but for the most part all you must do is load the code. It has already been coded and prepared for upload. For those who have interest in coding I have posted the code below. Most of this is the generic code provided by Adafruit, I just took out a few things lines to make it a little easier to transfer the data to excel.
Code: Copy everything between the lines
int sensorPin = A0; // select the input pin for the potentiometer
float rawRange = 1024; // 3.3v
float logRange = 5.0; // 3.3v = 105 lux
void setup()
{
analogReference(EXTERNAL); //
Serial.begin(9600);
Serial.println("Adafruit Analog Light Sensor Test");
}
void loop()
{
// read the raw value from the sensor:
float rawValue = analogRead(sensorPin);
Serial.println(rawValue);
delay(500);
}
float RawToLux(int raw)
{
float logLux = raw * logRange / rawRange;
return pow(10, logLux);
}
Photos of the Photometer:
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12 Comments
@xose awards a barnstar to programmer1200 for their awesome contribution!
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So cool! Thanks @programmer1200!!
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There has been a lot of information about measuring turbidity posted at Public Lab. Don Blair posted an excellent review of the common approaches to making DIY turbidity sensors. His focus was to make sensors which could be attached to data loggers and deployed at a body of water, but the information is also applicable to a laboratory device for use with cuvettes of water samples.
Don found that the standard way to measure turbidity is to sense the light scattered by the water instead of the light transmitted through the water as you do with this design. So the sensor is placed 90° from the direction of the incoming light. Some turbidity sensors also measure the transmitted light because having both measurements can provide better information and maybe information about the size of the particles in the water.
Most of the designs discussed by Don use LEDs as the light source. The better devices also have a lens to focus the light into a beam. It might be that a laser works as well as an LED plus lens, but I'm not sure.
Some turbidity sensors use visible light, but many use near infrared light. It's easy to find infrared LEDs and light sensors which detect near infrared. I don't know how critical the wavelength of the NIR emitter is.
Here is a potential BOM:
Arduino Nano ...............$2.20
NIR LED .......................$0.50
TSL2561 sensor.............$1.60
Total .............................$4.30
It's also easy to find red lasers for under a dollar.
Chris
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There is also lots of good information in this research note by Don about some testing he did.
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Thanks That's a lot of good information, now for hands on river work that design works pretty well , I was more working toward collect and then test back in the lab. I expect to get the price down farther to $10 after finding a cheaper light source and the 3d printed frames are .75 each. The research note will help alot on the programming.
Nano --> 2.20 Sensor-->3.50 Laser-->2.00 Frame-->.75 Total -- $8.45 Finished and working
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If I got it right, your photometer is measuring amount of light traveling through a solution or suspension. The loss of signal could be due to absorption of your red light, eg, by a green dye, or by scatter of light, induced by particles. To measure turbidity of non-colorless liquids, your may need to measure scatter typically done measuring the signal orthogonal to your path of light. That could work with your laser device. A suggestion: bakers yeast suspensions can be a very good, simple and cheap material to measure the scatter of practically colorless suspensions of tiny particles with a very well defined size. Just add a small amount of dry yeast to sugar water and incubate over night at room temperature. Fresh cultures should mostly consist of spherical living cells.
I had build some similar devices using comparable sensors, and my impression is that the brightness of your light source may be too high, resulting in saturation of the sensor. I would suggest to run the sensor at a maximum of 70% of its saturation volume. I guess you may find these helpful: https://www.instructables.com/id/A-Mimimal-Six-Color-Transmitted-Light-Spectrophoto/ and https://www.instructables.com/id/An-Inexpensive-Photometer-and-Colorimeter/ .
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Totally understand where your coming from , its very possible im having some loss because of that, to account for the possible over bright light source I built in a filter area , where one could insert a paper filter or what ever form of filter they would like . I'm still working on getting the light source to a good level so it doesnt interfere with the readings . I'm going to try your yeast method and see where that takes me. Thanks for the Info Holger
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@programmer1200, This is great! I agree with Chris and Holger that light scattering at a 90-degree angle is the standard approach for turbidity, and your setup looks roomy enough to accommodate that sensor placement. I'm excited to see this! I'd be curious to compare different suspended sediment concentrations and compositions. @Holger, great tip about the bakers yeast!!
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Thanks to you man!
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Hi, @programmer1200 -- how are you doing? Any updates about your project? Hope you're well!
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I'm doing great, school (zoology was harder than I thought lol ) been keeping my busy but I have not forgotten my projects, still working on perfecting the photometer. Should have an update here in a week or two.
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I posted a question this morning about how to choose between different methods for monitoring turbidity. Does anyone on this thread have some insights?
https://publiclab.org/questions/stevie/03-21-2018/how-do-i-choose-a-method-for-monitoring-turbidity
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