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'] Novel oxygen sensor (hearing aid battery) ?'
2004\06\06@164930 by John N. Power

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> From:         Peter L. Peres[SMTP:spam_OUTplpTakeThisOuTspamACTCOM.CO.IL]
> Sent:         Saturday, June 05, 2004 7:17 AM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      [EE:] Novel oxygen sensor (hearing aid battery) ?

> 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.

> Peter

The temperature dependence can come from changes in either the voltage
or the internal resistance. You might be able to separate the two effects by
switching the load current on and off periodically. The ratio of the voltage
change with load to the "off" voltage may be informative.

John Power

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