ecu voltage problem

[Tom Cloud]

I would investigate other things than the PS.  Your symptom
zounds like a glitch somewhere's else.  Not knowing your setup
nor your code puts me at a disadvantage, but I can't
see why the power supply would be good enough to allow the
confuzer to put out a pulse synchronized with the tach but
not good enough to allow it to adjust the width of said pulse ???
Still go back to ground loop, but how can that cause a fixed
pulse ??  Does the confuzer generate the pulse or does it
just load an external (or internal) counter with the pulse
width ??

>We are using a 7805 1 amp voltage regulator.  We also tried a 1000 uF cap
>between 12 volts and ground to no avail.  I am going to run over to the 
>ECU and analzye the ground situation since we had the computer
>running the engine on a stand but as soon as it was in the car it
>crapped out.  Other information: the regulator seems to put out 5 Volts
>down to a 7-8 volt input.  The cmos in the 68hc11 will work down to 4 1/2
>volts with little problem and can probably drop a bit below that
>sometimes. 
>Sean
>On Wed, 30 Apr 1997, Tom Cloud wrote:
>
>> >I am an FSAE student and we built an EFI computer for the competition.
>> >There seems to be a problem running it off the car's power supply, ie the
>> >battery.  When it is hooked up to the battery the computer holds pulse
>> >widths at around 1 ms per revoltution regardless of throttle position.
>> >When we hook it up to the standard voltage regulator used for testing in
>> >the lab the car works perfectly with full rpm and throttle range, but
>> >can't move because it is attached to an extension cord.  We're using a
>> >68hc11 processor.  If anyone has had any weird voltage problems like this
>> >any help would be appreciated.  Thank you,
>> 
>> What kind of regulation circuitry are you using to drop
>> the voltage from the automotive 12 volts to your circuit.
>> Keep in mind that your regulator needs to be able to deal
>> with voltages as low as 8 or 9 volts (cranking) to over
>> 15 volts, with voltage spikes maybe as high as several
>> hundred.  A resistor/zener or varistor input could squelch
>> the spikes (lo-R so you don't lose voltage from current
>> drain of circuit).  Put this before your regulator.
>> In-line inductors (chokes) work also, but they can
>> get big.  Also consider you may have some sort of
>> ground loop going on.
>> 
>> Tom Cloud <cloud at peaches.ph.utexas.edu>
>> 
>
>
>

Tom Cloud <cloud at peaches.ph.utexas.edu>