Battery Level Indicator - del00022
Description.
This
circuit uses a LM339
pdf, a quad comparator. LM339 pdf can work on single or dual supplies,
it has a open collector output that can drive 15mA, low power
consumption. The circuit is an untested design but it should work.
I did it as many
searches were made in my webpages with these keywords.
There are many better
circuits in the various circuit archives i have linked on the front
page, you just have to look around. When you measure the open
circuit voltage of a battery with a high impedance
DMM (10M), the value may be a bit misleading. Apply a dummy load to
bleed
the battery a bit so that proper readings can be taken on Load. The
load
below is a 100 ohms wire-wound fusible ceramic resistor which will heat
a
bit when you test 12V batteries.
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Theory of Operation.
R16 a 5W ceramic wire wound bleeder or dummy load. R15 is a part
of an attenuator for obtaining ranges. D2 is a protection clamp diode.
R10-D1 forms the 5V reference for comparators. Then an attenuator
obtains 1.2, 1.4, 1.6, 1.8 V steps for each
comparator. This circuit is similar to Audio Level meter or VU meter
circuit.
The comparator compares the battery sample voltage to the fixed
reference step. If '+' pin is more positive than '-', or is '+' is more
dominant, then output goes floating 'open collector', so No LED light .
But if '-' is more dominant the output transistor of comparator goes
low impedance or saturates or turns 'ON'. But only spec current can be
switched, do not compare with electrical switch 'ON'. Also on a
dual supply 0V is more dominant or positive compared with -12V, even
though it appears -12V is a big number. The direction of current is
what decides, all measurements are relative.
Data sheets and Information.
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