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Currently, I working on a project to make a car tracker device. At the moment, the device can work well, but I want to improve it.

The situation is that my device is running on a external power (lead-acid battery) and I want to send an alert to remote server when the device is in low-battery.

As far as I know, one way to do it is to check frequently the remaining of battery which is complicated (using more hardware and complex algorithm).

My design is based on an Arduino uno R3, and a Sim080 module.

I just need to trigger the remote server when it is in low-power, no need to define the accuracy measurement of remaining in battery.

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Since you haven't included info about hardware, just mentioned a device.

A low power detection circuit is quite simple, a OP-amp, zener diode and a couple of resistors/potentiometer is all whats is needed.

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  • I use arduino uno R3 + module Sim808. Can you explain in detail how to do it ? As I have a little experience in electronics and power consumption. – juggernaut156 Feb 22 '18 at 8:23
  • If you are using a Arduino it has several "A/D input" converter and all you need then is a voltage divider (two resistors) and a code that compare the current voltage with your "low-voltage" limit and sends a "Low voltage" message to the remote server. And please add as much info you can, DON'T use device, remote server as they are generic terms and it looks like you wan't a detailed answer! – MatsK Feb 22 '18 at 8:31
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As far as I know, one way to do it is to check frequently the remaining of battery which is complicated (using more hardware and complex algorithm).

but

I just need to trigger the remote server when it is in low-power, no need to define the accuracy measurement of remaining in battery.

You have the scope with this design to collect data which will help you to trigger this event at the best time - this is the great advantage of IoT designs compared with trying to implement a feature without two-way connectivity.

The lead-acid battery is a fairly simple beast. On charge, the voltage rises to around 14.2V, and will drop over time (at rest) to 12V. With a load, the voltage will drop a little - depending on the load. Close to discharge, it will drop faster. See this answer for an example discharge curve.

With a 10V zenner dropper and a clamping circuit, you can measure 10-13.3V full-scale using the ADC. This is enough to identify discharge, but you will want to monitor and adjust the threshold that you use. You might find that temperature affects the threshold that you use, along with time since the engine was running (and many other variables).

By collecting more data, you have the opportunity to make indirect measurements, and even to identify changes in behaviour which can give you early warning of faults.

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