Hi all,

I have just tried out something: A dyi oxygen sensor. It's a hearing aid
battery. It uses air for operation. The air is admitted through small
holes on the back of the button cell battery. The internal resistance of
the cell changes with oxygen content in the air. Thus by loading the cell
with a constant current load, the i.r. can be measured indirectly.

I loaded the battery with a resistor to give 2 mA of current and tested
what happens when the air supply is cut off, when exposed to an
oxygen-displacing gas (CHCFC electronic freeze spray at room temp.), and
when exposed to exhaled air. It seems to work although it has a pronounced
temperature dependence. The signal is in the mV range with about 100mV
range for 5-20% O2 (very roughly estimated), response under 30 seconds
full range.

I will try to use a different type of cell (with more holes in the back),
in a differential configuration, with one cell exposed to standard gas
(air) and the second exposed to the gas to be tested.

This could be good. Hearing aid batteries are widely available.

If you set up your own experiments, please share them.

Peter

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads