New laser pointer professions. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Laser pointers, which have recently appeared on sale, are intended primarily for teachers of educational institutions to use them when explaining graphic materials. However, such a pointer can also be used in everyday life, for example, for remote control of the operation of electrical and radio appliances. How to do this is described in the published article.

A laser pointer, despite its external simplicity, is a relatively complex product. It contains a semiconductor laser, automatic maintenance of a certain current flowing through it, an optical system, a battery of galvanic cells with a voltage of 3 ... 4,5 V, and a power button. The current consumed by the laser is 30...50 mA.

Although the power emitted by the pointer (wavelength 630...650 nm) does not exceed 5 mW, due to its concentration in a narrow beam, propagation losses are small. Laser radiation can be fixed at a great distance. However, it is strictly forbidden to direct the pointer beam at the eyes - this is dangerous.

The pointer can work in security devices, light phones, home-made toys, bird scaring devices, etc. For now, we will limit ourselves to a story about the construction of an automaton capable of turning on and off household electrical and radio appliances at the signal of the pointer. The pointer itself does not require any alteration.

The automaton (Fig. 1) contains a photodetector on a photodiode VD1, a voltage comparator on logic elements DD1.1, DD1.2, a pulse generator on elements DD1.3, DD1.4, a D-trigger DD2, two electronic switches on transistors VT1, VT2 , actuating element - electromagnetic relay K1 and power supply.

(click to enlarge)

The power supply is made according to a transformerless circuit with a quenching capacitor C6. The alternating voltage is rectified by diodes VD6, VD7, smoothed by capacitor C5 and stabilized by zener diodes VD4, VD5. Power is supplied to the microcircuits from the VD4 zener diode through the VD2 diode and the smoothing capacitor C1.

The device works like this. When the device is connected to the network, a high logic level through the C4R7 chain enters the input R of the trigger and resets it. The trigger output is a low logic level, the key on the transistor VT2 is closed, the relay is de-energized, the load is disconnected from the network. At the input and output of the comparator there will be a high logic level, and at the inputs of the elements DD1.3, DD1.4 - low, the generator is not working. At the same time, a high level is set at the output of the DD1.4 element, the transistor VT1 opens and turns on the HL1 LED.

How does the switch take place? The photodiode VD1 is illuminated with a laser beam, and the voltage across it is significantly reduced. The comparator, after discharging the capacitor C2, is triggered, and a low level appears at its output. A high level is supplied to the outputs of the elements DD1.3, DD1.4, the generator starts to work, the LED blinks, indicating that the photodiode is illuminated.

If we now turn off the laser or move the beam away from the photodiode, then the voltage on it will increase, the comparator will be set to a high output level, and the trigger will switch. A high logic level will appear at its output, the transistor VT2 will open, the relay will work and the closing contacts K1.1 will supply the mains voltage to the load.

In the case of repeated short-term illumination of the photodiode (until the LED blinks), the device will switch to its original state and the load will be de-energized.

Thanks to the use of a relay, it is permissible to connect a wide variety of electronic equipment to the device: radios, TVs, VCRs, etc. with any power supplies, as well as electrical appliances with electric motors, such as fans.

All parts of the device, except for the relay and the VD3 diode, are placed on a printed circuit board (Fig. 2) made of one-sided foil fiberglass. It is designed to use transistors KT315A-KT315E, KT312A-KT312V, KT3102A-KT3102D, microcircuits of the K176, K561, 564 series, any LED from the AL307 series (preferably in a plastic case). Diodes VD2, VD3 - any rectifier, VD6, VD7 - KD102B or similar low-power ones with a maximum allowable reverse voltage of at least 400 V and a current of at least 100 mA, zener diodes - for a stabilization voltage of 8 ... 10 V. Polar capacitors - series K50, K52, C6 - K73, the rest - KM, KLS, K10. Trimmer resistor R2 - SP3-19, constant - MLT, S2-33. The relay should be selected with a response voltage of 12 ... 15 V at a current of not more than 30 mA, for example, RES9 (passport RS4.524.200, RS4.524.201), its contacts must withstand the mains voltage and current consumed by the load.

A few words about the RES9 relay. According to the reference data, its contacts are designed for a voltage of 115 V. However, the long-term practice of using the relay in various devices has shown reliable operation of the contacts at a mains voltage of 220 V. Of course, you can opt for relays of the RKN, MKU-48 types, but the design dimensions will increase significantly.

The board together with the relay is placed in a case of suitable dimensions, made of insulating material. The photodiode and the LED are placed in the openings of the case side by side so that the LED serves as a guide and signals with its flashes that the laser beam hits the photodiode. To avoid interference and malfunctions, you need to install the machine so that the photodiode is protected from light from lighting devices.

Setting up the device comes down to setting its sensitivity (with a tuning resistor R2), the speed of response to laser illumination (by selecting capacitor C2), the blinking frequency of the LED (roughly by selecting capacitor C3, smoothly by resistor R5).

The automaton can be somewhat simplified by eliminating the generator. In this case, the output of the resistor R8, left according to the scheme, must be disconnected from output 3 of the DD1 microcircuit and connected to output 11. The elements R5, C3 are removed, the connection between terminals 2 and 4 of DD1 is removed, and the unused inputs of the elements DD1.3, DD1.4 are connected to the common wire. In this case, when the laser beam hits the photodiode and the comparator is triggered, the LED will go out.

A variant of a simpler machine is possible (Fig. 3), if it uses sensitive trinistors 2U107A-2U107E, which open at a small (less than a volt) voltage on the control electrode and a small (several microamperes) current in its circuit. Its basis is a trigger on trinistors VS1, VS2, which is powered, as in the previous design, from a block with a quenching capacitor.

Let's analyze the operation of the machine. After connecting it to the network, both trinistors will be closed, and the relay will be de-energized. If you illuminate the photodiode VD2 with a laser beam, then due to the photoelectric effect, a voltage will appear on it, which will go to the control electrode of the trinistor VS2, and it will open. The relay will work and turn on the load in the network - this will be signaled by the illuminated HL2 LED. Capacitor C1 will start charging (minus on the right output according to the diagram).

To turn off the load, illuminate the photodiode VD1. In this case, the trinistor VS1 opens, including the HL1 LED. The trinistor VS2 closes, since a negative voltage from the capacitor C1 is briefly applied to its anode. The relay is de-energized, the HL2 LED goes out, the load is disconnected from the network.

If now the photodiode VD2 is illuminated again, the trinistor VS2 will open, and VS1 will close, since a negative voltage from capacitor C1 will be applied to its anode. The load will be energized.

Experiments have shown that AL360A, AL360B LEDs work well as a photodiode in this machine, since they are based on IR emitting diodes. In addition, they are equipped with a focusing reflector, which increases their sensitivity to the laser radiation of the pointer.

The details of the machine are designed to work with the RES9 relay (passport RS4.524.200). They can be placed in a small housing (Fig. 4) made of insulating material. Holes for LEDs and photodiodes are drilled on the front wall of the case, and a power outlet is installed on the back.

When setting up the machine, a capacitor C3 and a zener diode are preliminarily selected. The stabilization voltage of the zener diode should be approximately 4 ... 5 V more than the relay operation voltage, and the capacitance of the capacitor should be such that the current through the relay is 15 ... 20 mA more than its operation current.

The disadvantage of the machine is its low sensitivity, which limits its control range.

When setting up the machine, electrical safety measures should be observed, since its parts are galvanically connected to the network. All soldering should be done only with the machine disconnected from the network.

Author: I. Nechaev, Kursk

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