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

[James Paul]

   Chris,

  A few things I can think of right away would be.....

  1) Put the micro and it's associated circuitry inside a metal box and ground
     the box.

  2) Try using a ferrite choke where the wires enter the box.  Just wrap the
     wires through the ferrite core a couple of times.  This should reduce 
     RFI significantly.  By the way, RFI is the culprit.  It is generated 
     because of the high tension spark discharge is so wide band, it covers 
     most of the RF spectrum.  Just like lightning does to an AM radio.

  3) Use a low value resistor ( <2 ohms) shunted by a low value (.01 - .05 uF)
     capacitance in the power line to the microcontroller unit to aid isolation
     from the battery that also feeds the ignition system.   

  4) Add a .1 to .5 uF capacitor between power and ground at the micro to
     aid in transient suppression.  You might want to add a 10 to 20 uF 
     Tantalum cap here too in parallel with the .1 to .5 uF unit to aid
     transient suppression even more.  

  5) Bring ALL ground leads to a common point to prevent Ground loop currents.


    Hope these suggestions help.  Let me know how you do on your project.


                                                     Regards,

                                                        Jim





At 10:18 AM 5/12/98 -0500, you wrote:
>Chris Vandrachek 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
>
>Chris Vandrachek 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
>
>
>
> Chris,
>
> I would like to help but would need more info. My first
>
>guess (usually wrong!) would be to look at the circuit
>
>between the coil and the MCU.
>
>Have you tried an inductor in series with the power supply
>
>of the MCU board?
>
> If you like, email a circuit diagram.
>
>
>
>  Walter
>