12V Low Voltage Alarm/Indicator.

Thread Starter

Rhine400

Joined Nov 9, 2020
5
Hey guys,

already got lot of informations out of this forums. THANK YOU FOR THAT.

I´m working on little project but can´t best solution.
In general I need a simple 12V low batterie alarm (with a low current, cut voltage by potentiometer, 1/60Hz Alarm Tone).

I created a circuit with a LM358 with a Trimmer Potentiometer and a piezo etc.
Works fine, but I don´t need a continuous alarm and the current was bit hight (10-20mA passive / 60mA active)

Now I thought making a sound each 1 minute (1/60Hz) is simple, but I have read so many solution that I´m not sure anymore what solution is the best.
Stay to the LM358 and add circuit for the interval tone? Is there any out of the box solution?
 

Thread Starter

Rhine400

Joined Nov 9, 2020
5
Didn´t draw it yet.
I bought this one out of the box:

As you can see here:
the guy also mentions 9,5mA in passive mode.
 

Dodgydave

Joined Jun 22, 2012
9,936
The second video is using a LM339 .

This is the correct circuit diagram .

It only uses one half of the chip so you can modify it for pulsing .

 
Last edited:

Thread Starter

Rhine400

Joined Nov 9, 2020
5
The second video is using a LM339 .
Oh sorry.

I think 10mA would be OK for a car-battery, but in case the voltage is low (buzzer on) the current is about 60mA which is too much. So I thought if I go with a LM358 circuit I should add the oscillator / timer in front of the LM358 to safe some energy...
But after my research I´m still unsure if the LM358 is the right way to go?
 

crutschow

Joined Mar 14, 2008
26,992
In sghioto's circuit, for better temperature stability you could use a TL431 for D1 instead of a Zener.
Its basic reference voltage is 2.5V, but you can compensate for that by reducing the value of R2.

Note that for a predictable trigger-point hysteresis (to prevent dithering) as generated by R4, there should be a small resistor in series with D1.
 
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