Build a Stunning Battery Status LED Flasher Circuit

Alerting When a Circuit Battery Reaches Its End, 5V to 12V Operating Voltage

A Battery-status Indicator circuit proves beneficial, primarily for monitoring portable test instruments and similar devices. The LED D1 flashes to draw attention to the situation, preventing unintentional prolonged operation. The circuit generates approximately two LED flashes per second, with an average current consumption of around 200µA. Transistors Q1 and Q2 are configured as a non-common complementary astable multivibrator: both remain inactive almost continuously, activating only when the LED illuminates, contributing to minimal current usage.

Circuit Operation

This circuit functions with power supply voltages spanning from 5 to 12V. The LED flashing can be adjusted to the desired battery termination voltage (situated within the 4.8 to 9V range) by modifying Trimmer R4. Slight variations in the values of R3 and/or R4 can accommodate these changes. As the battery voltage approaches its depletion level, the LED flashing frequency decreases abruptly, alerting the user. Naturally, once the battery voltage drops below this threshold, the LED will remain permanently extinguished. To maintain stability of the battery depletion voltage, diode D1 was incorporated to compensate for variations in the Q1 Base-Emitter junction due to temperature changes. The utilization of a Schottky-barrier device (such as BAT46, 1N5819, or similar) for D1 is essential; the circuit will not operate if a standard silicon diode like the 1N4148 is used in its place.

Circuit Diagram

Components

Note

Further reduction in the circuit's average current consumption can be achieved by increasing the values of R1, R7, and R9.