my bad prom

[thergen at svn.net]

If the input requires a 0 to +5v signal, don't power the 555 with +12v if
you're going to use pin 3 to drive the ecm input.  Pin 3 goes from near 
ground to near the positive supply (pin 8).  The 555 will work with
a +5v power supply on pin 8 which will result in a voltage swing of about 
0 to +5v on pin 3.

Tom

On Fri, 3 Sep 1999, Ken Kelly wrote:

> Mike,
> 
> 	This is from an email last year when I was doing the same thing.
> 
> > Easy.  Just get a 555 and connect it up as follows:
> > 
> > Pin 1 is Ground. Pin 8 is +12V. Connect a 0.1 uF ceramic cap between these
> > pins, with short leads, for bypassing. Otherwise it may misbehave.
> > 
> > Tie pin 4 to pin 8.
> > 
> > Tie pin 6 to pin 2.
> > 
> > Add a 3.9K resistor from pin 7 to pin 8. (A 3.3K will be close enough)
> > 
> > Add a 22K resistor from pin 6 to pin 7. (You could adjust this one for
> > precision setting, but it's not needed for this application)
> > 
> > Add a 1 uf capacitor (electrolytic OK) + side to pin 6, - side to pin 1.
> > 
> > Add a 0.1uf cap from pin 5 to pin 1.
> > 
> > Output is on pin 3. It will be approx.
> > -----------------------------------------------------------------
> > Have fun...
> 
> 		Ken
> 
> 
> Mike Rolica wrote:
> > 
> > OK so I know my prom is junk.  It's a hypertech (no It is not the piggy
> > back type-165ecm)now my OEM prom needs a signal from the vats module
> > (5v at 30hz square wave) I have the OEM service manual from gm (it is the one
> > that the mechanics use at the dealership, it's about 4"thick) I have access
> > to allot of them (86-96 and EFI gm car/truck) If anybody is interested just
> > email me. I can scan what you need and send it to you.  Anywayz,  the signal
> > the vat needs, is the amplitude of the wave from 0-5v or is it -5v - +5v?
> > How can I build something to bypass this?
> > Mike  Rolica :)
> > mrolica at meridian-mag.com
> > (519)-245-4040
> > EXT: 260
>