Getting rid of noise of car battery/alternator

[passion1]

Hi All

I would like to connect my pic16f73 to my car battery and run the pic while driving.
I was thinking of using the attached voltage regulator, but I was told that the power in a car is very noisy and I should add additional protection against noise to protect the pic?
In the attached circuit I'm using a LM7805 to bring the voltage down from +13.8VDC to +5VDC

Any suggestions what needs to be added to my circuit as to protect my pic, or can I continue to use the circuit in my car as is?
Any help will be appreciated!

[passion1]

In another thread the attached schematic was suggested to monitor voltage of a car battery.
Am I right in saying that, If I am not monitoring the voltage but merely wants to run my pic from the battery,
then I only need the portion included in the red box?
What would be appropriate components/values for Z1, D1, D2?
For Z1, what is best, a 18V transorb or a zener?
For D1, D2, is a 1n4007 good enough?

Thanking you in anticipation!

[mackrackit]

The only thing I would add to the first circuit and it may not be necessary, just a habit of mine, is a 4700uf on the 5 volt side.

[passion1]

Dave

Thank you for the suggestion.
Is the purpose of the 4700uf on the 5 volt side to smooth out voltage spikes?

[mackrackit]

Yes and no.
You should not have spikes coming from the LM7805. Spike being something more than 5V. You can pick up some high frequency noise and the 4700 will help with that.

The other thing a larger cap will do is help on brown outs. Depending on your app, it may not be a concern.

[skimask]

Dave
Thank you for the suggestion.
Is the purpose of the 4700uf on the 5 volt side to smooth out voltage spikes?

That, and probably a bit of a temporary power source for when you turn on your headlights and kill main power down to a couple of volts for a split second. It's not much, but it would probably save your PIC from losing it's mind.

[Luciano]

Hi,

See picture.

http://img259.imageshack.us/img259/5958/powersupply5vhr2.png
Best regards,

Luciano

[passion1]

Luciano

Wow! Thank you for a very comprehensive power supply design!
Can/should I still add the 4700uf to your circuit as well, as suggested by Dave and Skimask,
or does your circuit already provide a bit of a temporary power source for when one turn on the headlights?

[passion1]

That, and probably a bit of a temporary power source for when you turn on your headlights and kill main power down to a couple of volts for a split second. It's not much, but it would probably save your PIC from losing it's mind.
Skimask

Thank you for the explanation!

[Luciano]

Hi,

All depends from where you get the 13.8V.
Ignition key switch? Car battery direct?
Are you using the brown-out detection of the microcontroller?
How much current is drawn by your circuit?

Headlights are not a problem unless your car is like a Christmas tree. (Rooflights).
See picture below. (Starter/battery voltage).

Best regards,

Luciano

http://img132.imageshack.us/img132/7540/voltagels9.th.jpg (http://img132.imageshack.us/img132/7540/voltagels9.jpg)
(Click to enlarge the picture).

[passion1]

Luciano

Thank you for the graph!
I will be using the ignition key switch to activate the circuit.
My circuit will be driving a load of up to 30A via a mosfet.
In this case, can/should I still add the 4700uf to your circuit as well?

[Luciano]

Hi,

How much current is drawn by your board when the mosfet is not activated?
Are you using the brown-out detection of the microcontroller?

Best regards,

Luciano

[passion1]

Luciano

I have not measured it, but it is very little current.
I am not using the brown out detection.

[Luciano]

Hi,

Build a prototype and try it out.
Enable the brown-out detection.

Best regards,

Luciano

[passion1]

Luciano

Thank you for the advice!

[Darrenmac]

If you are still having trouble ty adding a choke in series with the incomming supply as well as capacitor on input and output of reg. Cars can be so noisey!