Tach input from spark voltage (idea)

[Grant Beattie]

On Sun, 20 Oct 1996, Johnny wrote:

> one box that uses coils that see about 400 volts on the primary side. Some
> of these systems use a standard 12 volt coil, some do not. I know that this
> answer isn't as cut and dried as you had hoped, but they are not all the
> same. If you are looking to do a "standard" ignition, the primary voltage
> is less than 12 volts. Are your concerns for an inductive pickup about
> saturation or calibration or?

The inductive approach works fine for single-cylinder (kart, lawnmower
<g>, ...) engines, but in a car, there are too many stray signals from the
other plug wires and such.  I started playing around with the sensitivity,
but that means I would need different pickups for different engines.  So I
thought maybe if I went back to the source... 

The range 12v to 400v is mildly discouraging.  I know national makes 
devices that might fit this application.  I was hoping to use an 
opto-isolator though, and the limited current range (1mA to 16mA) is 
tough to match to 12v to 400v.   Hmmm.

Thanks for the info,
GB

http://ourworld.compuserve.com/homepages/grantb
(Data acquisition for racing)