ADCIN car battery monitoring

[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.

[Archangel]

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.

DC flows through the wires, traces etc . . . R/F sorta crawls along the outside, and the .1µF strips it away

[mitchf14]

Thanks for your replies again guys, you've all been very helpful, what would the 5.1v zener do i know its for protection, it will start conducting around 3.3 v only when D1 as blown what is the purpose of that. For my voltage divider i want to build it with a 10k var in series with a 2.5K, and set the 10k at 5k, this will give me accuracy to tweak out the 5% tolerances. With a peak voltage of 15v which the battery should never get that high the out of my voltage divider will be 5 v. This will give me a wattage of 20 mW for the 5k and 10 mW for the 2.5 k now all this to ask my resistors should not get very hot but would this be enough to change resistance values as they get hotter, so as my resistors get hotter i would lose more and more accuracy or is the wattage so low i should not worry about it. Also is their a way to protect my ADCIN if someone would ever use two batteries and would connect them in series which would give me 24 v and 8 v at the output of my ADCIN, so for that to never happen, how can have no more then 5 v output into my ADCIN to protect it i'm trying to make it as dummy proof as possible. thanks