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