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?

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

Dave Plowman London SW
To e-mail, change noise into sound.

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?

What kind of a signal do you need, or think you need? What would be
suitable?

PWM to analogue
 

Dave Plowman (News) wrote:

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?

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..


http://en.wikipedia.org/wiki/Schmitt_trigger

PWM to analogue
 

In article ,
William Sommerwerck wrote:
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?

What kind of a signal do you need, or think you need? What would be
suitable?

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.

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

Dave Plowman London SW
To e-mail, change noise into sound.

PWM to analogue
 

In article ,
Jamie t wrote:
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..

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

--
*If God dropped acid, would he see people?

Dave Plowman London SW
To e-mail, change noise into sound.