Digital Pregnancy/Drug/Diagnostic test

There are colour sensor modules for the arduino, they detect colour light within the human vision spectrum, and give you a level of red, green & blue, they are not that expensive.
A while ago it was a popular pic micro thing to use a led as a proximity sensor or pushbutton, a led's capacitance changes with the light falling in it, so if you with a microcontroller light an led, then quickly in software and hardware put the led into a capacitance - timer circuit you can tell how much of its own light is being reflected, therefore you can use it as a prox.
At least I think thats correct, might be worth googling.
That way you can choose what colour, or colours/wavelengths you want to bounce off the target,, and get back a value of conductivity or what ever you call light conductance.

dr pepper said:

or what ever you call light conductance.

Click to expand...

usually referred to in terms of Absorbance (A) or %Transmission (%T). Where
A = 2-log(%T)

and

%T = (Intensity through sample) / (intensity of light through a blank)

It might be difficult to obtain samples of your target compound in DI water, which would certainly be ideal, so you are sure you're targeting only the desired compound instead of something else, or even multiple compounds. You may get errors using spectroscopy, since hydration levels will affect the strength of any compound in the urine.

This "electronic" test method is exactly the same as the purely chemical/biological one that only used the color-change "+" sine that used to turn clear to blue the + and clear we're confusing to users (a plus could (Incorrectly) be interpreted as not-pregnant to someone that did not want to be pregnant and (correctly) be interpreted to mean pregnant by someone who wanted to be become pregnant).

The solution was to simply hide the color change strip with an LED emitter/detector pair, look for a blue color change and display it as bluntly as possible.

This version also looks at the intensity of the blue and correlates hormone concentration to weeks of gestation. The wick in the body of the device controls how much liquid (urine) is moved up to the monoclonal antibodies in the chemical (hormone) sensor area of the strip.

Thanks All, this is all great advice.

gophert
You seem to know a lot about this.

In your previous post you say: "just use a reverse-biased LED of the same wavelength (cathode connected to Positive voltage,) and add a resistor of 10k to 100k ohms between anode of LED and ground. Measure voltage from ground to LED anode monitor absorption delta at various concentrations. Watch for ambient light bleed for noise."

Excuse my lack of knowledge of reverse-biased LED's, because I have none So I googled it, and I cant seem to find a reverse-biased LED. From what I see all LED's are forward-bias. If you could, please send me a link to an example of a reverse-biased LED.

Also, what would you suggest I use to measure the voltage. Could I use an Arduino for the prototype?

Thanks!

Scott

There's some stuff here (the website) https://www.thorlabs.com/navigation.cfm?guide_id=36 worth looking at.

The mode of operation is photovoltaic (0 bias) or photoconductive mode (reverse bias - negative voltage)

A LED should act as a detector when reversed biased and interfaced.

Also investigate a CCD array or camera. This is x-ray detector centric. https://www.aapm.org/meetings/04SS/documents/yester2.PDF