A QUEST: designing simple battery monitor circuit

[lamazoid]

Recently i had a need for an advanced battery monitor.
Most of such circuits have two LEDs (say, red or green). And they simply switch one with another when voltage drops below/rises above a given threshold.
But i want it to use SINGLE LED, operating in flash/constant ON mode.
(say, when voltage drops below given threshold, it should flash, otherwise - stay ON.)
I had no success with Gooogl'ng something appropriate, except microcontroller projects.

I can also use microcontroller and easily solve the task that way. I was raised in analog circuits world, but MCU's are part of today's reality and some time ago i also was forced to learn and work with them. But i don't like to use microcontrollers to just flash a led or make simple comparator - analog circuits do this easier and definitely look better
So, let it be "the worst case plan"

Let's design something simple and unconventional, just for brain exercising & fun.

here's a list of goals:

1. use of single LED. good voltage = constant on, low voltage = flashing.
2. simplicity. use of widely spread and cheap parts. standart logic ICs, basic Op-amps, etc. - allowed.
3. working voltage range 5-15V DC.
4. threshold of detection should be easily programmed. preferably with Zener diode or something like, e.g. just one non-adjustable part which can be easily replaced to get another level.
5. flashing rate 1-2 Hz.

What i think at the moment: get an lm386 and use one half as comparator, another as square wave gen (for flashing). certain voltage zener diode for comparator reference.

Waiting for your thoughts & comments

P.S. have a good summer, @all

[Gary Lecomte]

An LM386 is a Single Power Amp. Not Dual.
An LM393 is a Dual Comparator.

Constantly ON is a Waste of power on the Battery.

[lamazoid]

Jul 20, 2016 5:05:55 GMT -8 Gary Lecomte said:

An LM386 is a Single Power Amp. Not Dual.
An LM393 is a Dual Comparator.

Constantly ON is a Waste of power on the Battery.

oops, i meant LM358. i have hundreds of them

yes, constant on is a waste, but it's allowed by goal. (actually, the device will have very short operation time, then it's physically disconnected from battery)

[Gary Lecomte]

I am quite sure it is possible, Sorry but not something I am interested in working on.

I would suggest to Modify the one below, but use a dual LED (Green/RED) in a single package.
Your Op-Amp can Oscillate the Red, Than you get the Constant Green, Turning RED when Flashing

(Most of such circuits have two LEDs (say, red or green). And they simply switch one with another when voltage drops below/rises above a given threshold.)

[harryn]

For advanced batteries, especially Li types, the charge / discharge curves are very flat, and often temperature effects are larger than the voltage variation due to state of charge. A potential alternative is to actually measure the current flowing in / out of the battery using hall effect sensors. For example, these parts from Allegro look interesting.

www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx

I have not tried them yet, but I have a project that needs to measure battery state of charge as well.

[lamazoid]

Aug 4, 2016 15:19:10 GMT -8 harryn said:

For advanced batteries, especially Li types, the charge / discharge curves are very flat, and often temperature effects are larger than the voltage variation due to state of charge. A potential alternative is to actually measure the current flowing in / out of the battery using hall effect sensors. For example, these parts from Allegro look interesting.

www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx

I have not tried them yet, but I have a project that needs to measure battery state of charge as well.

yes, there are also some special MCUs on the market, for battery control. they measure, calculate and record total energy amount which comes in and out, charge time, charge cycles, temperature, etc...

but it's a higher level electronics, compared to what i want to design here