Voltage Alarm For Testing Battery Charge / Discharge Time

[kcarring]

I've been trying to conduct some experiments as outlined for the SSG and other variants, and when it comes to discharging (or charging for that matter) a battery, and trying to stay reasonable scientific about it... one needs to stop charge and stop discharge at certain voltages. Yet the circuits i test are of course, manual operation type devices.

So...

Can you make an alarm from an op amp like the LM324AN?

Or would you need a comparator? Does anyone have a simple circuit that will sound a buzzer or eminate sound from a speaker at a detected voltage? If I made one device and used it, for all tests, it's own consumption could then be negated, as it would be used in all tests.

[FRC]

Battery pack

Small 12v battery booster packs usually have three leds red,yellow,green. When
the battery is fully charged the green led lights up. Maybe you could use one of
these circuits somehow and have the green led set off a buzzer or something.

FRC

[Inquorate]

You want a zener diode and pot to the base of a pnp transistor. Zener and collector to battery positive. Emitter to buzzer to battery negative. That'll tell you when it reaches a charge voltage. Build another one with lower trigger voltage that runs an electric motor. You'd have to listen for it to stop though.