MCP9700A - Battery Monitor / ADC / Divider

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TMeyer
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MCP9700A - Battery Monitor / ADC / Divider

Post by TMeyer » Thu Nov 29, 2012 3:48 am

Greetings Ron:
In the article's section titled “USING THE FVRSETUP AND ADCCONFIG COMMANDS” in paragraph 3 you write….

“Using a voltage divider definitely won’t work. For example, suppose we set up a voltage divider on the supply line with two resistors of the same size. When the battery is fully charged, a readadc value will be about 128, because two equal resistors divide the ADC range in half. When the battery supply is on the verge of total. exhaustion, the readadc value will still be about 128; in fact, it will always be at the midpoint no matter what the condition of the battery”.

I don’t understand.

Would not two resistors of the same value divide the voltage in half? A fresh battery will provide one ADC reading and as the battery weakens the ADC value (always representing half of the voltage) will fall.

By coincidence, a project completed at home 2 weeks ago monitors a remote battery. The divider used was a 22K/10K configuration. This brought the 12V from the battery into the 3.75V range.

The project works and follows a remarkably similar structure to your code. Employing FVR, taking a reading, using modulus divide for a “decimal” and sending the result to the term.

Am I missing something?

Thanks

Terry

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