Electronic flasher. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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It is unlikely that anyone has not seen special police cars on the roads, equipped with either light "flashing lights" or flashing beacons mounted on their roofs. Such a "flasher" can be mounted on the roof of a car, which, together with a 3-hour generator, will give light and sound signals announcing the right of way on the highway and through intersections.

"Flasher" (Fig. 1) consists of two red (HL1, HL2) and two green (HL3, HL4) LEDs, switched on by the control unit. The basis of the block is a master oscillator made on inverters DD1.1 and DD1.2.

From the output of the generator, a signal with a frequency of about 20 Hz is fed to the counter DD2. A high level signal appears sequentially at the outputs of the counter. Diodes VD1 -VD4 are connected to certain outputs of the counter together with resistors R2, R3. The inputs of the inverters DD1.3, DD1.4 and DD5, DD6 are connected in pairs to the resistors. The outputs of the pairs of inverters are loaded on the corresponding pairs of LEDs - HL1, HL2 and HL3, HL4. Diagrams of signals at various points of the block are shown in fig. 2.

Consistently appearing at the outputs of the counter DD2, high levels switch the inverters through the diodes to a low level state at the outputs, thus turning on the LEDs. HL1 and HL2 flash when a high level appears at outputs 0 and 2 (pins 3 and 4, respectively), and HL3 and HL4 flash when such a level appears at outputs 5 and 7 (pins 1 and 6). Therefore, when the generator is operating at the frequency indicated above, the LEDs will flash twice, either red or green, simulating the operation of a real flasher.

All parts, except for the LEDs, are placed on a printed circuit board (Fig. 3) made of one-sided foiled fiberglass.

The LEDs are placed on the roof of the car model (Fig. 4) inside a plastic housing lightly painted around the edges with blue paint. Naturally, at each edge of the case there is one red LED and one green LED.

Establishing the device comes down to setting the desired flashing frequency of the LEDs by selecting the resistor R1.

Having slightly complicated the design, get a "flashing light" (Fig. 5), which provides alternate triple flashing of pairs of LEDs. Moreover, their flashes will be relatively short, impulsive. Some real "flashing lights" have such a mode.

As in the previous design, the master oscillator is made on the inverters DD1.1 and DD1.2, the pulses of which are fed to the counter DD2. RS-flip-flops of the DD3 microcircuit are connected to the outputs of the counter, which control the passage of the signal from the generator to the pairs of inverters DD1.3, DD1.4 and DD1.5, DD1.6. The outputs of the inverters are loaded on the same pairs of LEDs as in the previous design.

The principle of operation of this option is somewhat different from the previous one, therefore, the signal diagrams at different points are somewhat different (Fig. 6).

When the generator is running, high-level signals will appear sequentially at the outputs of the counter DD2. Such a signal at output 0 (pin 3) will switch the upper trigger of the DD3 microcircuit to a high level state at its inverted output. The diode VD1 will close, and the pulses from the generator will begin to flow through the resistor R2 to the inputs of the inverters DD1.3, DD1.4. LEDs HL1, HL2 will flash in time with these pulses. The fourth pulse will transfer the counter DD2 to a high level state at output 3 (pin 7). The low level that appeared at the output of the upper trigger will open the diode VD1 and prohibit the passage of the generator signals through the inverters DD1.3, DD1.4 - their outputs will be high. The LEDs will turn off.

The sixth pulse of the generator will put the counter into a state in which a high level will appear at output 5 (pin 1). The same level will be at the inverse output of the lower trigger according to the circuit. The diode VD2 will close, the generator pulses will begin to flow to the inputs of the inverters DD1.5, DD1.6, the LEDs HL3, HL4 will flash. After the LEDs flash three times, the high level that appears at output 8 (pin 9) of the counter will turn off the indicated LEDs. The LED switching process will continue.

The details of this device are mounted on a printed circuit board (Fig. 7) made of one-sided foil fiberglass. The location of the LEDs is similar to the previous version.

In addition to those indicated in the diagram, in both cases it is permissible to use microcircuits of the K564, KR1561 series. Diodes - any low-power silicon or germanium. LEDs - any domestic or imported with the highest possible light output. In place of the green LEDs, it is desirable to install blue ones for greater resemblance to a real flasher. Resistors and capacitors - any small-sized.

Author: I.Potachin, Fokino, Bryansk region

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