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PWM to analogue

I've fitted a new fuel injection system (MegaSquirt) to the old car - the original was analogue and rather crude.

It's working well but has an interesting side effect. There is an OBC which calculates fuel consumption etc which is now wildly out. It works by counting the time one injector is open to give the fuel usage. The MegaSquirt uses PWM with flyback current limiting to drive the injectors which I'd guess confuses it.

Any ideas on the best way to convert those pulses into a suitable signal?

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*If a pig loses its voice, is it disgruntled?

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.
Reply to
Dave Plowman (News)
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What kind of a signal do you need, or think you need? What would be suitable?

Reply to
William Sommerwerck

Pass the signal through a SI diode, a small filter cap on the Cathode side, and then, pass this signal to the input of a schmitt trigger inverter, comparator, gate etc....

This will give you a nice square wave for the duration of the PWM for the ECM to get a proper reading..

If you can't your hands on a schmitt trigger inverter/gate, you could always use the Trigger and Threshold inputs of a 555 timer. Those will give you a hysteresis window of 1/3 Vcc supply..

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Reply to
Jamie

The original setup just applied a pulse of DC to the injector for the required time. In other words, the amount of fuel was regulated by the length of the pulse.

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*Organized Crime Is Alive And Well; It\'s Called Auto Insurance. *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.
Reply to
Dave Plowman (News)

Excellent, thanks. I'll give that a try.

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*If God dropped acid, would he see people?

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.
Reply to
Dave Plowman (News)

Buffer them, then integrate them into a voltage with a capacitor, maybe. It might not be possible for the gizmo to work with such a system.

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  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
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Reply to
Bob Larter

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