[Diy_efi] EFI system data

[steve ravet]

The 20KHz during the on period is to provide current limiting for a
peak/hold injector?  It seems like you could do something clever with a
555 or two on each injector output.  Like have the injector output from
the MCU enable a 20 KHz 555 PWM circuit, where the 555 PWM ratio is
controlled by a decaying RC circuit.  Or a sawtooth output from a second
555.  Or something like that.  You don't want to do that in software
(but you already knew that).

--steve

Kent Martin wrote:
> 
> The MCU does have pwm output but I'm superimposing a 20Khz square on top of
> the injector
> on period. To do this I must have an interrupt at each toggle of the output
> or use another timer to
> stop the 20Khz timer. This would require two timers for each injector and
> this is not desirable
> as it has only 11 timers, and I need a few others as well. |A ballast
> resistor I would have thought would
> give a slower opening time and more non linearity of  volume with open time,
> plus it's a bit low
> tech for me.
> 
> Kent.
> 
> ----- Original Message -----
> From: <bill.shurvinton at nokia.com>
> To: <diy_efi at diy-efi.org>
> Sent: Wednesday, July 24, 2002 8:37 PM
> Subject: RE: [Diy_efi] EFI system data
> 
> www.bgsoflex.com/megasquirt.html
> 
> Chose an MCU with PWM outputs, much easier. OR use the tried and trusted
> ballast resistor method. I have yet to see measured data to show that this
> is any worse than a true peak and hold driver or PWM system. The inference
> being that, for OEMs the circuitry of a P&H driver was cheaper than a bank
> of big power resisitors.
> 
> Bill
> 
> -----Original Message-----
> From: ext Kent Martin [mailto:kentmartin at froggy.com.au]
> Sent: 24 July 2002 08:03
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] EFI system data
> 
> What's an MS style PWM?
> I'm using a micro to generate the PWM.
> I may run into trouble generating 10-15% duty because
> of processor load, will 50% kill the injector.
> Kent.
> ----- Original Message -----
> From: <bill.shurvinton at nokia.com>
> To: <diy_efi at diy-efi.org>
> Sent: Tuesday, July 23, 2002 10:39 PM
> Subject: RE: [Diy_efi] EFI system data
> 
> -----Original Message-----
> From: ext Bruce [mailto:nacelp at bright.net]
> Sent: 23 July 1995 13:02
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] EFI system data
> 
> ----- Original Message -----
> From: "Kent Martin" <kentmartin at froggy.com.au>
> <SNIP>
> 
> If you are using a MS style PWM to provide the hold current then start at
> 1Amp per injector, which is 10-15% duty cycle for a 2Ohm injector. Adjust
> till it works. Once you are tuned in, it may be worth backing off a little
> until you reach a minimum reliable hold current.
> 
> Bill
> 
> > What is the duty cycle required to keep the average injector open
> (assuming
> > a 20 Khz frequency)?
> 
> 20KHz?  Your not goin find and injector to operate at that speed.
> Bruce
> >
> > Kent.
> 
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-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com

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