interference from ignition systems

[Dan Zorde]

Try taking the power and gnd directly to the battery terminals (not car
chassis), ensure the box is connected to the the car chassis as a
shield.  Ensure no gnd from the circuit inside the box is connected
directly to the box (will compromise the shielding).  Decouple your
incoming power and gnd (from battery) to chassis via 0.1uF caps, also
connect a 1Mohm resistor from incoming gnd to chassis (helps remove
noise spikes and bleed off any static charges).

Also have a look at the FTP site there should be a copy of a nice psu I
use for our automotive equipment.  Can't remember what the file is
called though, but if you can find it you could rig up the filtering
section of the front end.

Alternatively (if possible), try putting a coffee tin (connected to
chassis) over the distributor, the police used to do this years ago,
when high power ignition systems came in and they started to interfere
with the radios.

Dan  dzorde at erggroup.com


On Tue, 2 Oct 2001 13:33:42 +1000 "David Sackett"
<david.sackett at optusnet.com.au> writes:
>
> I have been having trouble with accurate measurement of RPM and I
> believe it
> is due to interference from the ignition system.

> If the engine is running at 1000rpm
> occasional values of 3000, 5500 & 15000 will be calculated by the
> computer.
> I thought that the input and power supply filtering I had designed
> was
> inadequate so I constructed a new circuit board based on the
> megasquirt's
> power supply, coil based external interrupt trigger and TPS input
> (thanks
> for the design Bowling and Grippo). I still get the same
> interference!

> David




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