I'm building a robot that I plan on running off of 12 volt
sealed, lead acid batteries ( UPS Batteries )
One of my 'things to do' is to figure out how to have the
robot recognize that the batteries are running low.
Is there a simple circuit ( that won't consume a lot of power
it self ) that will report the battery charge level via a
couple of I/O pins or RS-232 signals?
Thanks - jack
The voltage of most batteries goes down as the battery is discharged. A
simple battery monitoring circuit merely samples that voltage.
One older method is to use a bargraph IC. These ive you output pins that
can indicate voltage within a fairly narrow range. The IC is intended to
connect to LEDs, which you can use for visual feedback. Pick one or two
pins to connect to your microcontroller as "getting low" and "really
low." Look on Google for some circuit ideas.
If you are connecting to an MCU with an ADC, you can connect a resistor
across the battery and load (a fairly high value to limit drain). Use
Ohm's Law to calculate the voltage.
Maxim and others make battery monitor ICs you might try out. Many of
these companies will send free samples. Some of these have 1- and 2-wire
serial interfaces. They're made for polymeer and rechargeable lithium
cells, and are probably more sophisticated than you need for lead acid,
A somewhat crude but workable method is to use a zener diode, which
"folds back" if the voltage drops below a certain level (essentially,
outputting a HIGH or LOW depending on battery level). You select the
zener based on the minimum voltage desired from the battery, and the
characteristics of the zener. Google should have circuit examples.
RS-232 wouldn't be as easy, but it could be done with a PIC or AVR using
just the analog comparator inputs. Some PICs and AVRs have serial
UARTs, but you may need a MAX232 chip or equivalent if you need real
Author: Constructing Robot Bases,
Robot Builder's Sourcebook, Robot Builder's Bonanza
Jack Snodgrass wrote:
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