infrasonic detector with mpx2102A

Good advice for dealing with the sensor's output signal, but I'm afraid the Motorola / Freescale part is not sufficiently sensitive for decent infrasonic measurements. merco can find a far more sensitive diaphram (diaphragm?)-style sensor, or perhaps he should consider a different approach entirely, such as measuring the airflow in and out of a reference chamber due to small low-frequency pressure changes.

Honeywell makes good products worth considering for either approach, such as low-cost "ultra-low pressure" diaphram-style sensors,

and highly-sensitive airflow sensors, like the AWM3200V and AWM3205V amplified sensors,

They don't seem to have downloadable pdf datasheets (that's awkward!), but the AWM3200 one-page engineering drawing shows a heater control, a heated-air airflow-temperature sensing bridge and a differential output amplifier with offset, to work from a single 8-15V supply.

They specify these sensors as pressure sensors, because it takes a pressure difference to force airflow through the sensors tiny holes.

--
 Thanks,
    - Win

First build the demo circuit from the data sheet to drive the sensor. This gives a voltage output, proportional to pressure. I'd then say you probably need to add a 'low pass' filter to the output, rolling off above

10Hz, to reduce the tendency to pick up higher frequencies. The output you then have will contain the low frequency sound you are looking for. You may well need to consider removing '0Hz' from your target, since otherwise you will continuously be sensing the barometric pressure changes, which will then probably swamp other signals you are interested in. Perhaps something like '0.01Hz to 10Hz', is likely to be more practical. This then allows you to add DC rejection to the output, and increase the gain significantly. If you actually want to 'hear' signals from this frequency range, then you will need to add a stable oscillator at perhaps something like 50Hz, and a mixer stage, so that you get frequencies in the audio band generated representing the incoming signal. Otherwise the signal is already suitable for sampling/recording.

Best Wishes

I read in sci.electronics.design that merco wrote (in ) about 'infrasonic detector with mpx2102A', on Wed, 5 Oct 2005:

Listen to your GF's heartbeat? Worth trying, anyway. (;-)

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

no it's for an intrusion detector... not for me...