thanks larry, i will follow word by word all your advice, really lots of
fun awaits me

RVP.


Larry Bradley wrote:

> I use the National LM2931 series of low dropout voltage regulators in
> marine engine applications. There is an adjustable version, plus a 5 volt
> foxed version. These are designed for automotive applications, where
> transient voltages on the battery can be quite high. Check it out in the
> National Semi web site
>
> http://www.national.com/design/index.html
>
>
> As to noise - filter, filter, filter. Use an RC filter on all inputs from
> sensors - the values will depend on the expected rate-of-change of the
> sensor data. I tend to use a 1K resistor and a 10uf capacitor with a
> 0.1 uf
> capacitor in parallel on all input signals in "slowly changing" systems.
> Tie all unused inputs to ground.
>
> Use a filter on the 12V input (before the regulator) to help keep
> noise out
> of the power supply.
>
> Don't use the automotive ground for sensor return if you can help it. For
> example, if you have a series resistor (shunt) to measure current, use a
> 4-wire connection for the shunt - connect it in the circuit to be
> measured
> with the normal leads, then connect two more wires to the resistor closer
> to the resistor body than the normal leads to use as your sensor wires.
> Then use an opamp in a differential configuration connected to the sense
> wires (if you need more info on this get back to me) to help eliminate
> noise on the sensor wires.
>
> Use a separate wire for the emitter of the switching transistor - don't
> just use the negative supply line to your PIC circuit. Connect this
> wire to
> ground at the engine block, or some such ground point. You don't want the
> switching current going through the negative supply line to the PIC -
> nasty
> spikes. I'd even be tempted to mount the switching transistor close to
> the
> coil, rather than as a part of the PIC circuitry, and just
> feed the base drive voltage to it from the PIC - again, with a filter on
> this lead - the filter values probably need to be smaller than 1k/10uf
> since the filter will effect the rise time of the switching pulse.
>
> And you might think about building it in a metal box, rather than a
> plastic
> one.
>
> Have fun!
>
> Larry
>
> At 02:56 AM 1/7/2003 -0400, you wrote:
>
>> Hi All,
>>
>> i'm developing a pic based automotive electronic ignition, it's based on
>> a mc10012 darlington as the main coil switch, a very low value
>> resistance for current feedback/sensing and a pic for controlling the
>> dwell angle at various rpm. in paper and in my desk works well, but i
>> think that the voltage regulator must be a little more than a 7805, so,
>> where i can find information (or schematics) for build a reliable
>> voltage regulator?, and what precautions i must follow to minimize
>> noise, etc? (it's for a jeep, and i don't want the motor to stall
>> climbing a hill)
>>
>> any help will be great!
>>
>> thanks
>>
>> RVP.
>>
>> --
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>
>
> Larry Bradley
>
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>
> Orleans (Ottawa), Ontario, CANADA
>

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