Low battery indicator in the flashlight. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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Rechargeable flashlights are often used in emergency situations. But you need to be sure that, having stood on the shelf for a long time, he will not let you down at the most inopportune moment. It is difficult to assess the degree of battery charge by the brightness of the light, it is extremely inconvenient to periodically check the voltage with a voltmeter. It is possible to make a control device with an LED, but it is not easy to find a place to install the latter on the lamp body, and it is not always possible to constantly monitor it. The proposed device, designed to quickly check the lamps of railway linemen, makes the lamp lamp flash if its battery is discharged.
The signaling device circuit is shown in fig. 1. When the battery voltage GB1 is higher than the stabilization voltage of the zener diode VD1, the transistor VT1 is open, a high logic level is set at the EI input of the DD1 microcircuit. Since this input is common to all elements of the microcircuit, their operation is prohibited. The logic level at the outputs of the elements (including pin 9) is low. Transistor VT2 is closed, VT3 is open, lamp EL1 is lit.
When the battery voltage drops, transistor VT1 closes. The high logic level at its collector and at the EI input of the DD1 chip is replaced by a low one, turning the elements of the latter into an active state. The pulse generator starts working on the elements DD1.1, DD1.2, DD1.4. Through the element DD1.3, the pulses arrive at the base of the transistor VT2, periodically turning the lamp EL1 on and off. The flashing frequency depends on the values of the resistor R4 and capacitor C1.
The printed circuit board of the signaling device and the location of parts on it are shown in fig. 2. By selecting the resistor R2, it is possible to change the response threshold within certain limits. If the light signal is not enough, you can supplement it with a sound signal.
To do this, from the two remaining free elements of the microcircuit (DD1.5 and DD1.6), an audio frequency generator is assembled according to the circuit shown in Fig. 3. When the EI signal is low, it starts to work simultaneously with the first oscillator that controls the flashing of the lamp. The sound frequency depends on the values of the resistor R7 and capacitor C2. A piezoelectric sound emitter ZP-1 is suitable as a BF1, but the best result is obtained with a "tweeter" from a faulty multimeter.
Author: A.Kalinin, Vologda
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