At 04:59 PM 11/1/2009, you wrote:
><capav8r@gmail.com>
>
>Bob:
>
>Put a scope on the tach gen output. The situation is the signal
>from the tach gen goes to a 5.1 V zener diode, then to a comparator
>against a reference voltage to generate a square wave.
>
>Attached is the picture of the waveform at low rpm (approx
>800). Note the spikes in the wave. Also, the voltage is near the
>zener voltage so the zener never gets driven into breakdown so that
>is why the unit has a flakey rpm reading at low
>rpm.
Agreed.
>So, would the waveform squaring circuit you posted in an earlier
>post work to square this waveform? If so, I have 28 VDC available
>in the aircraft. I'd need to use a 28-5 V converter chip to get the
>5 VDC on the collector as you drew it. Any suggestions for this?
I don't recall exactly what I sent you earlier
but this is probably similar.
Emacs!
This squaring circuit has a +0.6v threshold. Since
your 80mS, 5v trashy square wave goes above and below
ground, this will square it up nicely. The diode
keeps the negative excursions at high RPM from going
exceeding the zener breakdown threshold for the NPN
device.
Bob . . .
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( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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