Paul,
What would be required to use this on a 20B??
Don

I suspect minor changes in some of the resistors. Perhaps a 50% decrease in the
value of R4. Perhaps Tracy knows exactly. The principle I think is it is only
looking at one injector pulse and the circuit assumes there are four pulses.
Is this correct Tracy or is your computer computing the combined data
and putting out one pulse trains with period and width adjusted accordingly?

Of course the max reading in a 3 1/2 digit 0.2 volt voltmeter would be 1999
or 19.99 gallons per hour. Some other voltmeter module probably should be used
because at full power full rich 20B will probably suck down more than 19.99
gallons per hour. One could of course move the decimal point but the DC input
voltage to the voltmeter would be further down in the noise level at low
fuel flow rates. Long story and it would take several paragraphs to explain
this better. Better to change the voltmeter IMHO to something else like a
full four digits. I'll be interested in what Tracy has to say about this.

Paul Lamar

If there are two injectors on the 20B which are never open at the same time, you
could have two "D2"s -- one to each of those injectors. That would double the
voltage and probably raise it above the "noise level". Also, it's wouldn't be so
much a "noise level" as possible temperature drift; C5 filters out the noise.  Just
need to change the R3, R4 voltage divider. Use metal film resistor for R4.
BTW, I would use a 74HC14 or 74C14 instead of 74HC04.

Finn

Good idea Finn. The 74HC14 is a Schmidt trigger and is therefore more immune to noise.
A 4 1/2 digit voltmeter is about $20 dollars additional from Digikey.
BTW most run on five volts so the nine volt battery would be unnecessary.

Paul Lamar
 
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