ADCIN car battery monitoring

[mitchf14]

Hi guys i want to build a circuit for my second year school project i was hoping someone could give me some more insight on this circuit i found on this forum.

I touched it up the original circuit a little bit in visio and saved it as a pdf, i added some values that where missing, can someone tell me if they are accurate. And if you would be so kind to give me a explanation on how it works. I Have a general idea already how it works and i seems to be a nice little circuit just a couple of parts i have no idea why they are their.

[amgen]

tell how much you understand already..... as a starting point.
there probably are some unnecessary parts in there.
don

[mitchf14]

Well from i can see here D1 is just for protection in case someone would ever reverse the polarity's, and the 10 ohm in front is soften the blow of the D1. I'm guessing the 47uF cap is to block some ac, i was going to use a 50k var to get a more precise 3:1 ratio, The D3 and D4 is for protecting my pic for reverse polarity's also. If this is all correct, i just can't see what all those extra capacitors do.

looking forward to your explanation

[Archangel]

Well from i can see here D1 is just for protection in case someone would ever reverse the polarity's, and the 10 ohm in front is soften the blow of the D1.

Or give somplace to scrub off some current should the voltage cause the zener to fire.

I'm guessing the 47uF cap is to block some ac,

It does that, it also act as a quick voltage source when the load outstrips the power supply

i just can't see what all those extra capacitors do.

They provide a short circuit path to different frequency noise.

[Charles Linquis]

You shouldn't use a 50K pot as a voltage divider. The source impedance into the A/D shouldn't exceed 5K or so. I like to keep it below 2K. A 5K pot would be a better choice.

[precision]

Resistance should be 30K and 20K for full adc resolution.

12V
+
|
|
/
\ 30K
/
\
|
|------- V 0ut 4.8V
\
/ 20K
\
|
|
--
GND

According to Attachment.

.

[mitchf14]

Thanks for all your reply's guys, i keep seeing people putting a small capacitor in parallel with what is the purpose of that my teacher in school never mentioned anything about that is it important, in this circuit it shows 2 of them the 0.1 uF should do the trick.