Pulse doubler schematic

[Steve Ravet]

jdzura at csc.com wrote:
> 
> >I think I like Bruce's original idea the best, though.  Two 555s, each
> >in monostable mode, one on the positive edge and one on the negative.
> >That's one IC (556) plus some passive components, plus a couple
> >transistors to combine the outputs.  Battery voltage works fine.  It
> >also avoids programming the PIC.  You won't get a 50% duty cycle at all
> >speeds, but it doesn't sound like that's a problem since the ECM uses a
> >zero crossing detector.
> 
> I agree, KISS (keep it simple s.....) where ever possible. The only thing I worry
>       about is the drift and resulting pulse width change over time and
>       temperature. 

The 555 solution may not be good for driving an electronic speedometer,
but even with drift it should be fine for the ECM.  As someone else
pointed out, the ECM doesn't know about the rear end ratio, what gear
the trans is in (except 4th gear switch on 700r4s), etc.

> 
> If the ECM uses a zero crossing detector, does that mean all the signals are AC.
>       Also, what is the Peak to Peak Voltage level? Do we have any idea of what
>       minimum pulse width the ECM can detect?

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com