LASER PHONE

LASER PHONE

Materials about the specific features and infinite possibilities of lasers, including semiconductor, have been published in the journal “modelist-Konstruktor” (for example, No. 8’2001). Told also of how to adapt widespread laser pointer (LU) in a homemade optic dash, where it emitted the light pulse performs a function of photon bullets (see “modelist-Konstruktor” No. 12’2001). It was stressed that luminescence intensity and a number of other physical parameters LU depend on the voltage applied to the laser led.

 
Based on these and other publications, the most inquisitive of readers turn to the journal with an urgent request to inform, how by changing the illumination of the LU in accordance with signals of audio frequency and create a channel Amateur telephone communication using a laser beam. The answer can be the development of one of our active authors.

 
The advantages of the proposed homemade transceiver on LOU due to the peculiarities of the optical range in which it works. First, the device is simpler in comparison with conventional radioanlage. Second, the optical communication line is protected from unauthorized listening — “stranger” by his successor more difficult to infiltrate from outside of the beam.
 
Thirdly, it outlines a rather wide range where can be used the transceiver with a laser pointer from wireless or, say, transfer the sound of the television to stealth monitoring the acoustic environment of the protected object, listen to the calls in the depths of the apartment, a country house by the front door.
 
I developed the self-made device, somewhat similar to the famous Amateur sweetlife, consists of two parts: transmitter and receiver. Radiation LOU serves as a carrier of information, everything else is provided by simple electronic components.
In particular, the primary node of the transmitter is fairly powerful amplifier of sound frequencies assembled on the chip DA1 and several hang-on parts, providing the device normal operation mode. Sensitive to the input 1 of the IC through capacitor C2 is supplied to the information — electrical oscillations of audio frequency from an electret microphone ВМ1, DC power supply which is provided dvuhsistemnymi a voltage divider. Moreover, as the R2 uses a “podstreshny” that allows you to adjust the level of the input audio signal entering the amplifier.
 
The output of the amplifier through a resistor R6 to its inner contact connects laser pointer A1. Its metal housing has galvanic contact with the “plus” of power supply. Protect function pointers from the surge protector performs the Zener diode VD1.
 
The circuit diagram of transmitter () and receiver (6), as well as sketches of circuit boards (b) and (d), allowing to organize the Amateur communication link using a laser pointer
The circuit diagram of transmitter () and receiver (6), as well as sketches of circuit boards (b) and (d), allowing to organize the Amateur communication link using a laser pointer
 
As you know, working on LU — powerful special laser or led — has a unilateral conductivity. Given this, it is in addition to the modulating signal voltage is applied to some intermediate level set by resistor R6. The result has been the strengthening or weakening of the illumination of the pointer. That is sent by the transmitter and received by the phototransistor VT1 then the beam contains along with more information and the DC component necessary for proper operation of sweetelena.
 
The constant component of the signal light, which comes from the transmitter, holds the VT1 in the half-open state, and a variable causes it to open slightly more or slightly less than average. Accordingly, the voltage at the collector of the phototransistor will vary, but in time with the audio signals from the microphone of the transmitter.
The receiver amplifier is no different from the previously considered. Containing the information transmitted electric signal, which defines “podstreshny” R2 receiver, is fed to the capacitor C2 cuts off the DC component, and the variable is supplied to the input circuits DA1, as in the transmitter. Only the output of the amplifier instead of a laser pointer is the dynamic head of BA1, which converts the electrical signal 3H in sound waves, identical to those captured by the microphone of the transmitter.
 
In all experiments with a laser pointer need extreme caution. In particular, achieving stable operation of sweetelena should avoid even accidental contact with the beam. If necessary, masking optical communication, a light emitter of a transmitter and a phototransistor receiver should be placed in a hood, a tube or cover with a visor.
 
To complete both units acceptable fixed resistors MINTS with power From 0,125 to 0,5 W, “the trimmers” JS4-1A and as common inexpensive capacitor K73-24 (C2, C4) and C50-6 (all others). If the desired sensitivity of the microphone MKE-332, you must take it a modification to the alphabetic index or In G at the end of the name. Dynamic head can be of the type GDS 0.5-9; for more secretive listening will approach the capsule from handset or microtelephone ear the resistance of the voice coil of the order of 30-100 Ohms.
 
Sources of electricity may be three serially connected galvanic batteries type 3R12 or network adapters with an output voltage of 12 V. In the latter case, it is recommended to install the power switch in the circuit connecting the adapter with electrical 220 V.
 
Mechanical fastening and electrical connection of electronic components both in the manufacture of electric circuits on printed circuit boards or split from the foil on one side of plastic with a thickness of 1 to 1.5 mm Laser pointer and phototransistor are placed on the walls of the respective blocks, or are submitted beyond the housing of the receiver (transmitter). If both parts of sweetelena supposed to be placed stationary, it is expedient to provide a bracket or a stand with sockets, allowing you to quickly and unambiguously specify the desired optical axis “of the emitter — phototransistor”.
Yu PROKOPTSOV

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