The simplest 12v low-battery chirp possible. Which off the shelf components?

[Ed.Kloonk]

I've noticed a few peeps on here and also folks in my 'hood are suffering from flat battery syndrome.

For people with lawn mowers, boats, even cars, could we design a very low-power smoke-alarm type of chirp when a battery is getting flat?

Whats the best way to get lowest possible power consumption, 555 or transistor?

[sleemanj]

A microcontroller that goes into deep sleep and wakes up periodically for a few ms to check, a linear reg with low quiescent current, and a piezo beeper.

These are all things I have on my shelf at least.

[ozcar]

If you want a smoke-alarm type of chirp, what better than a smoke alarm chip?

[Ed.Kloonk]

The circuit I imagine would be much more simple for a beginner to tackle. I'm talking vero-board.

Or does such a design chew too much current?

[Ian.M]

A microcontroller that goes into deep sleep and wakes up periodically for a few ms to check, a linear reg with low quiescent current, and a piezo beeper.

These are all things I have on my shelf at least.

It will also need either a micropower OPAMP to buffer a very high impedance potential divider, (to keep the quiescent current of the actual voltage senseing circuit low enough, or a complimentary pair of MOSFETs, to switch the top end of a low-Z divider + level shift from the MCU up to the P-MOSFET gate.

The circuit I imagine would be much more simple for a beginner to tackle. I'm talking vero-board.

Or does such a design chew too much current?

Everything the MCU can do towards the objective on a few tens of uA has to be implemented chip by chip, and if they are hobbyist friendly through hole parts, they are unlikely to be extremely low power.  Also the complexity will be considerable - you need to compare a divided down proportion of the supply voltage to a reference with minimal quiescent current then gate power to the chirp circuit, which must be fairly energy efficient if you don't want to make the problem worse if it triggers when there's no-one around for a couple of days to deal with it, so odds are the simplicity of using a 556 will come with too high current consumption.   I'm thinking: slowly charge a capacitor till there's enough voltage to start an oscillator which provides the audible signal and runs on the energy in the capacitor till it runs out to produce a chirp.

Various ATtiny MCUs can be programmed as Arduino 'boards' using an ordinary Arduino loaded with the  ArduinoISP sketch, so using a MCU isn't the barrier to beginners you think it is.

[ledtester]

It will also need either a micropower OPAMP to buffer a very high impedance potential divider, (to keep the quiescent current of the actual voltage senseing circuit low enough,

I imagine for this application one could forego the opamp and simply calibrate the ADC readings in software.

[strawberry]

active beeper/blinking LED activated by ultra low power cmos comparator
everything above some mA might drain car battery flat within a month

[Zero999]

TLV6703, with a couple of resistors, a decoupling capacitor and a pulsed piezo buzzer.
https://www.ti.com/lit/ds/symlink/tlv6703.pdf

[Ian.M]

Yep, the TLV6703 looks near ideal for the application.  It ticks all the boxes except novice friendly through-hole, and enough output current capability to directly switch significant loads.

However, as T.I. say it can be used on a 'DIP Adapter Evaluation Module', putting it on a SOT23-6 breakout is unlikely to cause instability, so the rest of the project can use through-hole construction.   If necessary, the limited output current capability is easy to solve with a PNP emitter follower, permitting beepers with >40mA inrush current to be used.

Unfortunately there's still the issue of getting the average beeper current low enough to be a negligible drain on the battery, in case the alarm isn't noticed for a while.  Ideally you want the average current to be smaller than the expected self-discharge, which for a typical smaller automotive battery can be as low as a few mA equivalent discharge current.  Therefore the beeper needs to be efficient, and also pulsed with a low duty cycle.

[exe]

Those are called voltage supervisors, there are plenty of them. E.g.: https://www.ti.com/power-management/supervisor-reset-ic/products.html .