Blow sensor?

--- For a nice little low-mass thermistor that you can self heat:

Then hook it up like this:

+V---+-------------+------+------------+ | | | | | | [R4] [R7] [R1] [R2] | | | | | +---[R6]--+ | | | | | +----[C1]-----+------|--+---|+\ | | | | | >--+----0UT | | +------|-/ [RT1] [R3] | U1 | | [R5] | | | GND>-+-------------+------+-----------------GND

Select R1 to self-heat RT1 by a few (?) degrees above ambient, then select R2R3 to make U1+ less positive than R4R5 makes U1-.

Select C1 (and the voltage differential between U1+ and U1-) so that slow changes in ambient temperature or moderate airflow past RT1 won't cause U1+ to go more positive than U1-, but that a sharp puff of air will. When that happens, the resistance of RT1 will increase quickly, causing the voltage on the R1RT1C1 junction to rise quickly. That quickly rising slope will then propagate through the smaller reactance it sees through C1 than a more slowly rising slope would, pulling the voltage on U1+ more positive than the voltage on U1-, pulling the output of U1, a voltage comparator, momentarily high.

-- John Fields

^ with less attenuation

--
John Fields

Any suggestions for a sensitive thermistor or otherwise to act as a blow sensor, dont really need a calibrated or accurate response, just detect the presence or otherwise of a short pulse of moving air, like someone blowing across something.

Hot wire anemometer seems a bit fragile and kinda struggling to find a thermistor that dosen`t need a hurricane blowing across it to change.

Any Suggestions ?

Thanks Adam

I once used an elecret microphone as a simple blow detector in an electronic flute project. Rectified the output through a capacitor and sampled the voltage level with an A/D input of a microcontroller. Sensitivity is affected a lot by the method you use to direct the airflow into the microphone.