Using automobile power point to power stamp?

cutsrock

I am going to use the power point in my automobile to power both a GPS receiver and my stamp.· Will the stamp need anything besides regulating the power to the 5 Vdc(Vdd) that will be provided through the Voltage regulating circuit?

I am including the schematic.

The Bitmap file does not show well so I included a word doc also.

·

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EPIC FAILURE -·When everyday run-of-the-mill failure just isn't good enough.

Post Edited (cutsrock) : 3/25/2008 1:16:38 AM GMT

Mike Green

Your schematic would work fine with a 12V Gelcell battery powering just the GPS and Stamp, but an automobile is very very noisy electrically. You should really have a lot more filtering ahead of the regulator. At a place like RadioShack, you can get filter chokes for automotive use with electronics. Put this in the +12V supply lead. Also beef up the regulator's input capacitor at least to several hundred uF and use a 25V or 35V electrolytic. I'd also suggest a fuse before the choke. Even if the GPS runs off the 12V supply, I'd give it the benefit of the choke and electrolytic and connect the GPS to +12V at the regulator.

You might connect a diode in series with the +12V supply after the fuse and before the choke to save you if the battery ever gets connected backwards. It happens.

cutsrock

Thanks Mike, I appreciate your responce. I am in the process of implementing your suggestions. I have a 1 amp fuse protecting the GPS and intended attaching the stamp Vin after that fuse, but attached it before the fuse. The GPS Vin can be an unregulated 8 VDC to 40 VDC, optimized for 12 VDC. Typical operating power is 800mW. This voltage drives a switching regulator with a nominal 5 VDC output, which powers an internal linear regulator, producing the system Vcc.

My plan is to: Add filtering, beef up the input capacitor, add a fuse befor the filter choke, and connect the GPS a the +12V at the regulator.

Will post updated schematic when done.

Thanks again Mike

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EPIC FAILURE -·When everyday run-of-the-mill failure just isn't good enough.

Post Edited (cutsrock) : 3/25/2008 3:32:53 PM GMT

QuattroRS4

Perhaps a few worthwhile links - in terms of filtration ..

www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol2/col/nv53.pdf

http://forums.parallax.com/showthread.php?p=645131

As Mike has pointed out - the automotive environment is a noisey place .. a suitable supply/regulator design is critical
www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,P36533
is a switched mode regulator I.C made by Linear technology - particularly suited to automotive apps..


Regards,
John Twomey

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'Necessity is the mother of invention'

cutsrock

Thanks John.· I will review the information you passed along.· I did update my schematic using a RF Choke and Diode, but not sure if I made the correct selections.

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EPIC FAILURE -·When everyday run-of-the-mill failure just isn't good enough.

Mike Green

Schematic looks pretty reasonable. The LM2940 regulator is protected against reverse polarity by itself, but the input capacitor is not and the diode will protect both.

cutsrock

Thank you, MIke. Will now proceed with my ptototype.

Jim

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EPIC FAILURE -·When everyday run-of-the-mill failure just isn't good enough.