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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Receiver in infrared communication line. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / infrared technology Schematic diagram of the receiver in the IR communication line is shown in fig. 61.
Here DA1 is an amplifier-shaper that converts an IR flash illuminating the BL1 photodiode into a voltage pulse with an amplitude of U10@Uc4 (diagram 1 in Fig. 62). Single vibrator, made on the elements DD1.1, DD2.1, etc., expands this pulse * to tf1@R2 C5@15 ms (diagram 2 in Fig. 62) to delay its decline (1) at the input C of the counter DD3 and the formation of a "click" of duration tf1, in a sound generator made on DD2.5, DD2.6, BF1, etc. Single vibrator DD1.3, DD2.3, etc. generates a pulse of duration tf2@R4 C6@1,5 s (diagram 3 in Fig. 62), allowing unhindered counting of pulses in DD3 only in this time interval. The receiver is activated by the front of the first IR flash. It forms a short (tr@R6-C7) a pulse at the input R of the counter DD3 (diagram 4 in Fig. 62), which sets the counter to the pre-start state (it corresponds to 0 - low-level voltage - at all its outputs), and the first unit is recorded in the counter with a decay of a pulse of duration tf1. If the photodetector receives pulses following at a frequency of 2 Hz (remember, IR flashes follow with this frequency if the sensors on the protected object are not disturbed), then output 4 (pin 5) of the counter DD3 remains 0, since the front of the fourth pulse (it will appear in 0,5x4=2 s - at the end of the interval allowing the account tf2 =1,5 s) counter DD3 will be returned to its original state.
The receiver behaves differently if it receives IR pulses with a repetition period of 62,5 ms, i.e. - alarm signal. Since 62,5x4 \u250d 2 ms < tf1,5-3 s, the fourth pulse will transfer the counter DD4 to the state "000100" (5; 1 appears at its output 1 - a voltage close to the supply voltage), the counter in this state will self-lock ( signal 8 at input 1.2 of element DD9 makes it insensitive to signals at input 1), and the red LED HL16 turned on and 5 Hz clicks of the sound generator will bring the alarm to others (diagrams 6 and 62 in Fig. 1,25). This will continue for approximately 2 s (tf0,25 -0,25), after which there will be a XNUMX second pause and the alarm will repeat. When the connection is interrupted, the receiver behaves differently. If the receiver does not detect an IR flash on the time interval trev (trev = R11 C8), the capacitor C8 is discharged through the circuit VD6, R11, DD2.3, the transistor VT1 opens to saturation, the voltage across the resistor R8 increases from -1.4 V almost to the supply voltage , a low-level voltage is set at the output of DD XNUMX and the sound generator begins to emit a monotonous signal with a frequency ftone@1/2R14 C9. With the appearance of the first IR flash, the capacitor C8 quickly charges through the circuit R10, VD5, the tonal radiation stops and the receiver begins to analyze the incoming signals. The printed circuit board of the receiver is made of double-sided foil fiberglass 50x50 mm 1,5 mm thick (Fig. 63) in the same way as it is done in the IR transmitter. The photo head of the IR receiver (BL1, DA1, etc.), which is highly sensitive to electrical pickups in a wide frequency range, must be shielded. The screen is made of tin, its pattern is shown in fig. 64. The dashed lines here are the places of the folds. The bent screen is soldered in the corners, its bottom is leveled and, having installed it in the desired position on the null foil (it is shown by a dashed line on the board), it is soldered to it at two or three points.
Structurally, the IR receiver can be made as shown in Fig. 65. Here: 1 - receiver housing (black polystyrene 2 ... 2,5 mm thick); 2 - holder of a 7-fold hand magnifier (the handle is cut off); 3 - its lens; 4 - printed circuit board; 5 - screen of the photo head; 6 - photodiode FD 263-01. The holder of the magnifier is glued to the front wall of the case, which has a hole with a diameter of 35 mm (glue - pieces of polystyrene dissolved in solvent 647 or in RS-2). The distance between the coaxial photodiode and the lens should be close to its focal length. This will concentrate the incoming light flux on the photodiode and significantly increase the sensitivity of the photodetector to weak signals**.
The same requirements are imposed on the receiver mount as on the transmitter mount: it must be conveniently aimed and securely fixed in the best position. If, according to the conditions of communication, the IR receiver must be taken out into the street (for communication, for example, with a car standing at the end of the house, or with an apartment at its other end), then it is better to compose it in two parts: external, in a moisture-proof housing-hood of which they put only the lens and the front head, and the inner one with everything else. These parts are connected with a thin three-wire cable ("+", "-", pin 10 of the DA1 chip). The receiver can be supplemented with an acoustic emitter of higher power, for example, a dynamic head, included as shown in Fig. 66, or the piezo siren ACT-10 (Fig. 67), which maintains sufficient power even with a reduced supply voltage. As preliminary tests showed, the length of the IR communication line with the IR receiver and transmitter described here reaches 70 meters. A significant increase in it can give a transition In an IR receiver, the lens diameter is more important. With its increase, the illumination of the p-p junction of the photodiode increases and, accordingly, the distance from which the IR flash of the emitter can be fixed to the adjustable optics - if instead of a fixed lens with its approximate focusing, you use a lens from an old camera with focusing by distance, "Range "transmitter" can be increased by another 1,5 ... 2 times or more by increasing the brightness of the IR flash.
On the other hand, in communication lines not exceeding 20 ... 25 m (a car or a "shell" under the windows of a 3 ... 4-storey building, a window of a house on the other side of the street, etc.), optics may not be required in general, in any case - in the IR receiver. *) Recall that with moderate illumination, the duration of this pulse is close to the duration of the IR flash itself. With intense, from a closely located emitter, for example, it can increase by 3 ... 5 times or more due to the relatively slow "resorption" of charges in the p-n junction of the photodiode.
*) The beam divergence angle in the IR transmitter lens, its so-called aperture, must correspond to the IR diode lobe (see the radiation angles of the IR diodes in Appendix 3). Then the lens will "collect" all its radiation. Publication: cxem.net
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