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Mon 26 Oct, 2015 02:55 pm
I am using a pic microcontroller to monitor a 12v lead acid battery. The pic is a 5volt device with an internal 10bit A/D converter. The circuit power is derived from the battery under test via a 7805 regulator.
The A/D uses an internal reference voltage of 5v and so will have an output range of 0 to 1023 for a 0 to 5v input.
The battery voltage is fed to the analog input pin via a 2 resistor voltage divider to bring the input voltage within the 5 volt range of the A/D.
The problem is that a 12v lead acid battery is considered flat at approx. 11volts and fully charged at 12.8 volts.
So I am only working with a 1.8volt range which means that the A/D is not using it’s full resolution. How can I turn a 1.8volt range into a 5volt range referenced to 0v?
@Lostboy,
Holy Cow, Boy, but that's a good q. First reaction: Reprogram the microcontroller. Otherwise one of these devices
https://www.google.com/?gws_rd=ssl#q=dc+voltage+step+up+converter
...would step it up. But how to get rid of the unwanted 11v is another problem. Simplest way an 11-v zener diode of course
http://www.ibiblio.org/kuphaldt/electricCircuits/Semi/SEMI_3.html#xtocid1093412
...although you'd be at the mercy of temperature while I'm sure there's a far more accurate and reliable way if slightly more expensive. But at 84 I've forgotten almost everything
Doubtless we'll hear a better way from a knowledgeable a2k lad
@Lostboy,
Come on somebody, help us out
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