@xose awards a barnstar to programmer1200 for their awesome contribution!

So cool! Thanks @programmer1200!!

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

There is also lots of good information in this research note by Don about some testing he did.

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

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/ .

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

@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!!

Thanks to you man!

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.

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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