power supply noise filtering

Ethan

·i want to use my basic stamp in my car and use the car's batery as my power source, i called parallax tec and they said i would definately need to do something about noise, they were very vague, does anyone know of a good source of information that could help me? or has anyone gone through this with their project? any help would be great, thanks

Forrest

Here's a +5V power circuit for automotive use www.seetron.com/an_vpwr1.htm

N8YX

The only quibble I have with that circuit is their choice of power connections. A car's cigarette lighter
socket is a questionable thing at best. You may consider running a fused power lead from the "AUX" connection
in your car's fuse box to the circuit. Better still, go directly to the battery - don't forget to insert an on-off
switch in series with the lead - along with an indicator light - or you may end up with a dead battery
should you forget to turn your project "off" and leave it running for a long period of time.

Post Edited (N8YX) : 11/23/2005 12:41:17 PM GMT

Chris Savage

Ethan said...
·i want to use my basic stamp in my car and use the car's batery as my power source, i called parallax tec and they said i would definately need to do something about noise, they were very vague, does anyone know of a good source of information that could help me? or has anyone gone through this with their project? any help would be great, thanks

Ethan,

·· If Tech Support seemed vague, it's probably because we didn't provide an exact answer to your power supply filtering questions.· This would be nearly impossible to do, since the noise in a given system can vary or be non-existent altogether.· We have no way of knowing.· We can simply point out possibilities which you will then have to research.

·· I see Forrest provided you with a link to the one published on the Scott Edwards site, and that's a nice circuit.· But it also may be overkill.· At one time that circuit was probably necessary in some automobiles, but more modern cars have cleaner electrical systems, in part due to improvements in technology, but also in part due to the increasing number of controllers now present in automobiles, for such things as ABS brakes, Air Bags, Climate Control, Cruise Control, Traction Control, etc.

·· So you can see that there are a lot of variables involved, including when the car was made.· Your question actually come after I was charged with testing the stability of the electrical system in a current car, a task I will be working on next week.· In this test case I will be running a BS2, DS1620·and a DS1302 with no power supply filtering, from the cigarette lighter socket in my car.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

japer

hello Forrest
Thanks for the Link
Just what i was looking for.

japer

Beau Schwabe

Ethan,

Here is voltage regulator filter design that I have used in a "noisy" electrical environment
with great success. It's similar to the one that Forrest provided a link to, but this version
provides additional filtering on the output of the voltage regulator.

http://forums.parallax.com/attachment.php?attachmentid=39280

Description:
The "first" diode from Vsupply in conjunction with the 1000uF cap creates a typical Diode-Capacitor
buffer. The "third" diode (Output of the regulator) forms a second Diode-Capacitor buffer with the
10uF. The "second" diode (Regulator Ground) is a bias diode to the "third" diode. The 100uF simply
provides more stability between the main regulator output and ground.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Forrest

Beau,
Won't that diode on Vout drop the voltage down to 4.3V?

Paul Baker

Actually no, because he cleverly placed a diode on the ground line of the regulator meaning it will be 1 diode drop above true ground, do the math and you'll see they offset each other. [noparse]:)[/noparse]

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·1+1=10