Low-volts alarm

Posted on Jul 8, 2012

This inexpensive dc supply-voltage monitor sounds a warning when the voltage falls below a preset value. It is ideal for monitoring rechargeable batteries since it draws only a few microamperes when not sounding. The voltage at which the alarm sounds is determined by the zener diode. When the voltage falls below the zener voltage, the alarm sounds.

Low-volts alarm
Click here to download the full size of the above Circuit.

The alarm tone is determined by the RC time constant of the 39 k resistor and 0.01 mf capacitor.

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