LED voltage indicator. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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LED voltage indicator. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The device is designed for light indication of the voltage value of batteries or power supplies. It indicates three voltage levels: less than normal, normal, more than normal. In the first case, the two-color LED flashes red, in the second it is permanently lit yellow (orange), and in the third it flashes green.

The indicator scheme is shown in fig. 1. Voltage comparators are assembled on operational amplifiers (op-amps) DA1.1 and DA1.2, and on the resistor R4 and the emitter junction of the transistor VT1, connected in the opposite direction, there is a reference voltage source (about 6 5 V) Capacitors C1 and C2 increase noise immunity indicator.

LED voltage indicator

Logic elements DD1.2, DD1.3 made a generator of rectangular pulses with a repetition rate of several hertz. Element DD1.1 performs the function of 2I-NOT, and an electronic key is assembled on the transistor VT2.

The device works as follows. The comparator at the op-amp DA1.1 switches when the supply voltage is at the lower limit of the normal zone, and the comparator at the op-amp DA1.2 switches near the upper limit. When the voltage is below normal, the output of the op-amp DA1.2 is a high logic level, and the output of DA1.1 is low. As a result, the output of the DD1.1 element is a high logic level and the generator starts to work. Transistor VT2 periodically, with the frequency of the generator, opens and the left LED according to the scheme (red) flashes at this frequency.

When the voltage is normal, high logic levels appear at the outputs of the op-amp, and low at the output of the DD1.1 element. The generator is not working, there is a high logic level at the output of the DD1.4 element, so the transistor VT2 will open. Both LEDs will shine continuously, creating a yellow or orange overall glow color.

When the voltage exceeds the upper limit of the normal zone, a low logic level will appear at the output of the op-amp DA1.2, the generator will start working and the green LED will flash.

In addition to those indicated in the diagram, the device can use dual (K140UD20) or single (K140UD6, K140UD7) op-amps, the K564LA7 chip, any transistors of the KT312, KT315, KT3102 series, any suitable multi-colored LEDs - either two single or one two-color with a working current of 5 ...20 mA, for example ALC331A. Trimmer resistors - SPZ-19, constant - MLT, S2-33, polar capacitors - K50-6, K50-16, non-polar - K10-17a.

All parts are placed on a printed circuit board (Fig. 2) made of double-sided foil fiberglass. One side is used as a common wire (power minus), the leads of the parts to it are passed through the holes in the board. The mounted device is shown in fig. 3.

LED voltage indicator

Establishing the indicator is reduced to the selection of resistors R5, R6 to obtain the required brightness of the LEDs. If it is necessary to change the frequency of the generator, select capacitor C4. The operation voltage of the comparators is set by resistors R2, R3.

Author: I. Nechaev, Kursk

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