Re: Audio Tachometer for 2 stroke engine

On 24 Apr 2005 09:59:04 -0700, "BobG" <bobgardner@xxxxxxx> wrote:

>Oh you old guys are just full of crap. A 50 cent electret mic in a
>plastic bag and an opamp preamp into an edge detect on a pic would work
>just fine. Just measure the period of the zero crossings of the pops
>and log the max values into eeprom every second or so. You near
>Orlando? I'll help you with this project no prob.

I used electrets in a fan-failure application. We made a vacuum-formed
fan tray with little notches for the electrets to be near the fan
blades; these were bare-motor, unenclosed fans, so we got close. I
found that the electrets saturated easily with this much pressure
blast. That was OK with me, because I bandpass filtered (MF-10s) the
signals to determine fan failure. But for a wide-range measurement,
I'd suggest a low-sensitivity dynamic mic or something less likely to
saturate. Saturation will lower ambient rejection, so you might wind
up measuring the RPMs of the Harly that's passing you.

Agree that there should be plenty of signal, and processing should be
simple; no FFTs or anything like that.

Sounds like more experimenting, and less talking, might be in order
here.

John

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