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Dgswaner
05-19-2010, 03:19 PM
I'm using a MCP3208 ADC to read some Srarp IR sensors. I thought that since I will have a few extra inputs that it would be nice to be able to measure the charge of the batteries.

could someone point me to a circuit that I could use to proportionately drop the voltage within the limit of this ADC? my Max voltage is set to 5v.

Thanks

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DGSwaner

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"When in doubt, use C4" - Jamie Hyneman, Myth Buster

Timmoore
05-19-2010, 03:25 PM
2 resistors should do. A fully charged battery will be more than 12V, so prehaps a 10K and a 5K between the battery +ve and gnd, (10K to battery +ve) and connect the adc between the 2 resistors. then 0-15V will map to 0-5V at the ADC.

StefanL38
05-19-2010, 09:28 PM
Hello DGSwaner,

there are a lot of webpages "trying" to explain electronics. My personal oppinion about most of them: they are crap for beginners.

This one seems to be quite good:

Lessons In Electric Circuits -- Volume I DIVIDER CIRCUITS AND KIRCHHOFF'S LAWS (http://openbookproject.net//electricCircuits/DC/DC_6.html)

especially the attached picture shows what Timmore meant with two resistors.

http://openbookproject.net//electricCircuits/DC/00107.png

best regards

Stefan

Dr_Acula
05-19-2010, 09:33 PM
In the 5% E12 resistor values the closest you can get is 4.7k and 10k. In the 1% range, you can get 20k and 10k which divides more accurately into thirds. If you are stuck and (say) only happen to have 10k resistors you can put two in series to get 20k.

Or you could put two 10k resistors in parallel to get 5k above.

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www.smarthome.viviti.com/propeller (http://www.smarthome.viviti.com/propeller)

Dgswaner
05-19-2010, 10:46 PM
Wow, that's incredibly simple. I was anticipating a very complex design.

Thanks

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DGSwaner

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"When in doubt, use C4" - Jamie Hyneman, Myth Buster