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A simple 2 electrode chemiresitive sensor using baking cups

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Tammy507

New Member
I am no electronics student. So pardon me if i asking a lame question.

For a science fair project, I am trying to build a simple two electrode sensor with a chemiresistive film connecting the electrodes which will absorb volatile organic compounds in the human breath.

The goal is to measure resistance change before and after exhaling breath on different subjects and draw a conclusion.

To make chemiresistive film, we will using carbon and tetracosane hydrocarbon powder and bake in the 100 c baking oven for 30 seconds to make a thin film connecting the electrodes.

Also we will need to make lot of sensors (atleast 100) for testing on different subjects.

So we got this weird idea to use baking cups instead of PCB to perform our test. So the idea is we poke two parallel copper wires into a baking cups (non-conductive and can withstand 100c for 30 seconds and cheap) with 2 electrodes 3 mm apart and make chemiresistive film about 10mm x 6 mm joining those electrodes and connect multimeter to the ends of the copper wire and measure resistance before and after blowing air on to it.

I am planning to put the sensor under bottom opening 125 ml bottle and blow air from mouth using a straw using the top opening.

The bottom of the bottle are going to have 2 holes for the 2 copper electrodes so i can connect digital multimeter to both ends to check resistance change while blowing air.

This way i can prepare multiple home based sensors for my high school science fair project.

Please let me know if this would work as analternative to a PCB.
 

alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO!
Instead of us guessing if it would work, why don't you simply spend 5 minutes to try it and see if it comes up to your expectations? ;)
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
This is a lousy article https://en.wikipedia.org/wiki/Van_der_Pauw_method and I don't have the scientific paper anymore, but you might use "sheet resistance" instead. The idea is basically, to place 4 contacts (V+, I+, V- I-) symmetrically along the perimeter, do an I-V curve; electrically rotate it (4PDT switch) and do it again. Plug it into a formula and get "sheet resistance". The formula removes the effects of placement, The contacts can be made with " conductive silver paint".

4-point probe http://four-point-probes.com/four-point-probe-theory/ will likely not work because because your sample is too thin, The head is usually made of spring loaded PCB contacts. You can set the current, so that resistivity in ohms/square is measured directly.

In both cases, if you know the thickness, you can convert to resistivity in ohm-cm.

R= p/L/A where Rho is the bulk resistivity, R resistance, L = length and A cross-sectional area.

Chinese made PCB's are really cheap.
 
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