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by mrmu on Fri Mar 15, 2013 2:23 pm

Hi, I would like to develop a turbidostat with an optical density sensor. From what I've seen, I'll need a photo diode and an IR emitter. I was wondering your thoughts on this and if you have the equipment and/or a tutorial to build this?


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Re: Turbidostat

by EasternStarGeek on Sat Mar 16, 2013 12:01 am

If you want to roll your own, you need an LED and a Photodiode both facing in the same direction, into the water. Suspended particles in the water will scatter the light, reflecting some of it back onto the photodiode. The tricky part isn't so much the electronics, it's controlling the optical properties of the measurement environment. Once you understand the basic principle involved, you can certainly experiment.

On the other hand, If you don't want to re-invent the wheel, most modern dishwashers use them. Take your pick... ... nSearch=GO!

I especially like this one, and wouldn't mind playing with one some day:
Note the small size- the header connector appears to be a 4-pin, with 0.1" spacing.

You can probably buy one much cheaper than you can make one- even just to dissect and fool around with. It would still be a non-trivial challenge to get one of these to work, considering that you are unlikely to get much documentation with it.

By the way, such a device is called a Turbidimeter ("-meter" = to measure). I've used them before while doing control system jobs in the wastewater treatment industry.

The suffix "-stat" means to regulate or control.
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Re: Turbidostat

by zener on Sat Mar 16, 2013 4:54 pm

EasternStarGeek wrote:The tricky part isn't so much the electronics, it's controlling the optical properties of the measurement environment.

Exactly. And I love the dishwasher sensor idea, I never thought about that at all.

Now, I have some wastewater experiencee also, and some experience with turbidimeters. And I never heard of Turbidistat either. So I looked it up on the source of all knowledge (Wikipedia...) and it turns out there is such a thing, and it is used to measure some organic growth?? Is that what you are doing?

Any way, there could be a lot of ways to go about that.

But... if we restate your question as "I want to power an LED and then measure the light that falls on a photo-diode" then that is a simpler question. You could do it with a couple of resistors, a bettery and a multi-meter. However, if you want to make device with a CPU and a display, etc., the Arduino would probably be a good choice. Maybe if you explain more about what you want to end up with then others can give some ideas.

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