[Diy_efi] Ignition Pickup

[marko.cosic]

Hi all

I've been asked by a friend to make a little 'black box' to pick up an
ignition signal from the coil and output a similar pulse at half the
frequency to the tacho.

Its for a 1000cc V-twin Moto-Guzzi bike, origionally had an unreliable OE
ignition system and has been replaced with an electronic wasted-spark
system. Unfortunately the wasted spark means the tacho reads tiwce as fast
as it should and so he needs a little black box to eliminate every other
pulse.

How should I go about this, and what further info do I/you need? The spark
is from two (6v)  ignition coils wired in series, positive end connected to
ignition pos 2/3, negative end switched by the electronic ignition module.
Big bike, so "proper" 12v is available.

I initially thought I could 'just' stuff a d-type flip-flop on there wired
to halve output frequency, totally neglecting to think about the ringing
voltages across the LT side of the coil - resulting in a bike htat didn't
start for 10 seconds, and then one very hot, very smelly d-type lfip-flop
with BBQ protection diodes!

I'll no doubt get asked, so yes there is a potential commercial aspect to
this, but nothing special - a dozen or so units then if they work about 50
more, and they'd have to retail at <£20 so I'd have to be able to make them
for ~£5 to sell at £10. "Commercial" yes, but onyl some 'funny-money' for me
that I can spend on my car without feeling guilty ;-)

--
Marko
Land-Rovers; Rover 820 Turbo
http://homepage.ntlworld.com/marko.cosic



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