How do I reduce ignition noise. (HELP!!)

[Sandy]

Start off by getting a scope on the reset line and lookin at what it sees,
this is start point one. Next check the power supply with the scope and see
what kind of trash is on that.  A filter cap large uF size and a .1uF will
help, look at the powersupply for the SUBDRV board on the EFI Ftp site for
simple power supply. Run the CPU off a seperate supply and see if it still
resets. If so, then you may not have enough supply to run a coil and the
CPU from the same. All external leads that attach to the PC board and
sensors are antenna and will bring back a load of crap into the CPU and
related circuits,  again, check the amount of trash with a scope. A simple
filter can help, check out mouser/digikey for some EMI/RFI filters.
Grounds are very inportant, good grounds and shileding are mandatory. Also
in general, check for good design rules in the CPU board, all parts should
have a bypass cap close to the VCC and GND as pratical, and the last gasp
for getting it working is to have the CPU IN A METAL BOX. Again note that
the leads will act as antenna right into the box, so a ferrite bead on the
incomming wires may also help.

Just some things to try, but use the scope as a way to see what is really
getting hosed, could just be the power supply boucing from the kick of the
coil, could be the reset line and bouncing, could be a lot o' things, but
start with the scope on the power and work around. If you don't see a lot,
put in metal box, and filter all leads into the box. The Halltech unit when
I openend it up (thus voiding the warrenty) really didn't have a lot, but
they have it pretty well shielded in the metal case so that alone may be
the problem.

One question, if you did anything with wirewrap, it will not work. ;-) Lots
of antennas...

Sandy (rambeling, and spelling badly)

At 01:10 AM 5/12/98 -0700, you wrote:
>To all in EFT land:
>	I have recently designed and built a simple EFT system based on a
>Mot. HC12.  All has gone well until now.  I can't keep the MCU from
>reseting whenever the ignition fires.  I am only a sophomore EE student so
>I don't exactly know where to start.  
>
>Here is a quick outline:
>	-The MCU is physically isolated from the coil etc (5ft), but they
>	share the same battery.
>	-I'm using a standard points ignition...I'd do a electronic, but I
>	have to be done by this Friday.  
>	-The MCU supply is regulated with only a LM2935 (an automotive
>	specific device).  Only a .1 cap on the inputs.
>	-It seems that reset occurs most whenever a open arc is present,
>	arcing in distributor cap included.
>	-The problem is independent of my triggering pulse (from
>	coil)...so I'm guessing it is due to voltage spikes/drops or it is 
>	"in the air" (EMF?).
>
>I don't know what to do and I gotta have the done by Friday for a design
>competition.  Any advice would be greatly appreciated!!!	
>	Thanks,
>	  Chris Vondrachek
>          EE student, University of Portland
>  	  chrisv at egr.up.edu
>