[Diy_efi] Re: new EFI controller

Marcell Gal cell at x-dsl.hu
Thu Mar 13 01:03:07 GMT 2003


Hi Bill, 

> Lets put it another way. Propose me a better way and I will build it and run
> it on my MS stimulator with whatever is your preferred load and compare it,
> in operation to the 3 Bowling methods for both Inj_on time, inj_off time and
> heat dissipated. 
>
> This way we can have some area for discussion. Hopefully fruitful, as there
> are people out there planning to run 8 1.2 ohm hosepipe injectors off the
> MS, and that does present challenges.

This sounds great. I like the approach.
If they want bank efi, running some in series might be of interest.
If they want sequential efi with low impedance injectors,
then PWM current limiting is their friend. 

In pwm current limiting it is really a good idea to have a
low voltage rectifiing or schottky diode and/or bipolar transistor
when limiting, and maybe inactivate it and
have a high voltage flyback zener for the final switchoff. 

PWM current limiting can be controlled by the ECU, or other circuitry
(AVR megasquirt can control 5 or 6 PWM * current-limited injectors from
hardware, original megasquirt is probably inferior in this manner). 

If you want to drive more sequential injectors than
your ECU can do from hardware, then PWM masking must be
maintained by external digital or analog circuitry.
I'm now tending to go digital, because it can handle the
last on_pulse much better. (eg: dividing the master pulse's
remaining time to integer number of periods after the
injector has reached the peak current) 

I had an analog solution for injector driving pwm
limiting circuit: 

http://x-dsl.hu/genboard/injector/
Klaus came up with another. Klaus' has faster injector switchoff,
mine have other advantages. 

> However I would say, in the context of an automobile, if the flyback power
> zener is dissipating less than a watt then there are bigger fish to fry in
> efficiency terms.

yes, naturally. I just suggested a very simple thing, to
connect something to VCC instead of GND. Not becuase it does
not work the way it is, just to make it a little better.
It seemd to costs $0.
It just happened, that the proposal had been misunderstood
and blown up. And it just happens, that in the particular
application it costs rather $1, which is more
than the cost of 1 kWh energy in the car, so .... ;-) 

 Marcell 

Atmega 128 has 6 PWM channels in hardware, but I still
have to check if one is used for a counter for
(event-queue) interrupt. 


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