555 EFI again...

[Walter Petermann]

Matt Beaubien wrote:
> 
> Walter,
> 
> > Here it is:
> >
> > http://brokersys.com/~corsaro/wiring_diagrams/555fe.htm
> >
> > let me know what you think.
> 
> 
> What sort of input is needed for the
> trigger? It looks like maybe the neg side of a points-type ignition system,
> correct? Would it work with a generic HEI module firing the coil?

  Any pulse that goes below at least 0.8v . Points type for sure, and
  any ignition that grounds coil- . I'm not familiar with HEI. 
> 
> Also, with the setting described in the circuit, what sort of output vs
> inputs can be expected?

  It's a simple 'point slope' adjustment. You set the maximum pulse 
  width you expect at 1-atm using the R of the 555 RC circuit, this is 
  the 'point', then you pick an operating point e.g 2500 rpm and set
  the gain of the op-amp, this is the 'slope'. The output pulse
  will be a (almost) linear function of the MAP voltage. 
> 
> Lastly, what can be used to fire injectors? I know saturated type (high
> resistance?) can be fired using just a transistor (how about a TIP-120?).
> What about a P&H type? Is a driver required like what's been discussed in
> the past?

  The simplest would be anything that can handle up to 5A. Then a power
  resistor in series with the injector (~6 ohms?) and a 'fly-back'
  diode between collector and injector power supply.
  However(!)..I have heard about an IRF6210 that supposedly uses
  PWM to control current. This would be perfect. I am trying to get
  some info on it, as soon as I do I'll put up another page with
  some driver circuits.

  One word on circuit application. The idea behind it was to drive an
  extra injector during high loads, low manifold pressure. I don't
  think it's going to work very well if it's the sole source of fuel.
  For a stand alone efi the pulse width has to be a function of MAP*RPM.
  Although you might get away with using MAP plus O2 feedback and a very 
  rough ride :). I'll work on adding O2 feedback to the circuit.

  regards,
   Walter

Fuel equations:
http://efi332.eng.ohio-state.edu/diy_efi/archive/archive_num_19;lines=70-235