Megasquirt on lawnmower

[Robert W. Hughes]

Most of the lawnmower type magnetos use a set of points. The wire coming
up to the kill switch is connected to them and the signal there is quite
similar to the signal on the usual inductive switching ignition. It is
probably a little more sensitive to extraneous current drain so you
might want to buffer the input to the optocoupler with a transistor -
one of the simple tachometer circuits would work.

> It actually is quite easy to trigger MegaSquirt with a magneto. This is why 
> I used an optocoupler:
> 
> Wrap a few turns of wire (2 -3 turns is enough) in a loop about 1 inch or 
> so in diameter, and pass the spark plug wire thru the loop. Ground one end 
> of the loop and hook the other end to the TACH input.This will trigger 
> MegaSquirt all day long, and reliably, unless the plug fouls out. The 
> back-biased diode keeps reverse voltage from killing the optocoupler. You 
> can even eliminate the 330 ohm current limiting resistor - the average 
> current in this setup is so low no damage will occur to the optocoupler.
> 
> - - Bruce
> 
> 
> 
> >------------------------------
> >
> >Date: Fri, 09 Nov 2001 19:58:48 -0800
> >From: "Michael Gough" <mdg3369 at mac.com>
> >Subject: Megasquirt on lawnmower
> >
> >Hey all,
> >Just a little on the megasquirt powered lawnmower. Sounds like a good idea
> >for fooling around but.....
> >Most (All) lawnmowers I've seen have a magneto (sp?) for the spark. This
> >could cause you trouble for the RPM signal.

-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
Houston, Texas "The city with too much Oxygen"
rwhughe at ev1.net

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