[Diy_efi] pwm explanation

[Bino Lardo]

ok thanks

the pwm mode was to create a/d converter but I understand that saturated 
just need 12v? correct me if I'm rong? also what how could I set a interrup 
whit a missing thoot wheel




From: steve ravet <sravet at arm.com>
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>Subject: Re: [Diy_efi] pwm explanation
>Date: Fri, 31 Jan 2003 13:22:36 -0600
>
>The open/close signal to the injector is not usually referred to as PWM,
>it's just the injector on time.  PWM comes in to play if you have a low
>impedance injector that needs current limiting.
>
>Are you trying to use the PWM hardware to open/close the injectors?
>injector timing is usually synchronized to engine position, but the your
>PWM hardware probably won't do that, it's synchronized to the clock that
>runs the chip.  There have been discussions in the past about fueling
>that is totally asynchronous to engine position, but I don't remember
>the pros/cons.  Some archive searching should turn it up and you can
>decide for yourself.
>
>If you use the PWM hardware, then your software needs to decide on fuel
>delivery between 0 and 100% of the injector's capacity depending on rpm,
>map, or whatever else your inputs are.  Then it updates the PWM hardware
>accordingly.
>
>If you want synchronous fueling then you'll have an interrupt that comes
>from a cam or crank sensor.  The interrupt routine will load a one shot
>timer with a value according to the fuel requirements calculated, the
>timer output will drive the injector.  That's an example, there are
>other ways to do it.
>
>You have saturated injectors, they should measure something like 12 ohms
>or so.  If so then only an output stage to drive the injector is
>needed.  If you had PnH injectors (~2 ohms) then you'd need some kind of
>current limiting circuitry, either an additional PWM stage or a circuit
>that reduces the applied voltage based on the amount of current drawn.
>
>--steve
>
>Bino Lardo wrote:
> >
> > Hi
> >
> > I would like to know if can help me whit the pwm to drive the injectors.
> > I use a microcontroller to make something like the megasquirt. I 
>understand
> > how to create one voltage but where im lost is how do I determine the 
>amout
> > of time the injector is on ( a other timer?) and if the voltage has to 
>be
> > steady or if it varies during the operation of the injector. the 
>injector
> > are saturated. the microcontroller is a atmega 128.
> >
> > thanks!
> >
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>--
>Steve Ravet
>steve.ravet at arm.com
>ARM,Inc.
>www.arm.com
>
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