Infrared "business card" generator with encoder. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / infrared technology

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On fig. 38 shows a schematic diagram of an IR generator that forms a packet containing N pulses, where NО{1,...,1023} - can be anything within these limits*.

Here DD1.1, DD1.2, R2, C1 is a controlled multivibrator, the excitation frequency of which is f@160 kHz (f=1/2 R2 C1); DD2 - 14-bit binary counter; R3C2 - a differentiating chain that forms from the meander decay ( 1 at the output of DD1.3) a short - 5 ... 10 μs - pulse that opens the normally closed transistor VT1; VD1-VD10, R6 - encoder (diode-resistor "AND"), the number and placement of diodes in which N is set; SB1 - the emitter on button.

When the power is turned on at the input R of the counter DD2, a "single" amplitude pulse is generated, setting it to its initial state (in this state, a low-level voltage is set at all its outputs), and the multivibrator, having made seven idle "turns", enters the normal mode of operation. Meander frequency at the output 7 DD2 (fourth digit of the counter) F=f/2^4=10 kHz. With appropriate intervals - Tp@100 µs- will follow each other and 5...10-microsecond IR flash emitter BL1.

Rice. 38. IR business card generator (click to enlarge)

The generation of IR flashes will continue until a high-level voltage appears at the output of the encoder - the input of the DD1.6 element, and, accordingly, at its output - a low-level voltage that closes the multivibrator. The number of pulses in a packet depends on the number and "weight" of the diodes in the encoder:

N=VD1+2VD2+4VD3+8VD4+16VD5+32VD6+64VD7+128VD8+256VD9 +512VD10, where: VDi=l if the VDi diode is installed in the encoder, and VDi=0 if it is not. Since N = 1023 and Tp = 10^4 s, the duration of the packet will obviously not exceed 0,11 s.

The amplitude of the current pulse in the emitter itself - in the IR diode BL1 - depends on the supply voltage of the generator Up and the resistance of the resistor R7: Ii = (Up-2,5) / R7 (Ii - in amperes, Upit - in volts, R7 - in ohms) . Here, obviously, I@0,07 A.

However, there is no particular need to strictly follow the indicated ratings and types of elements that make up the generator. Almost any npn transistor with h1e>21 and Ik max>100 mA can be taken as VT100, and IR diodes such as AL1A, AL115A, AL118B, AL119A, etc. can serve as the emitter BL147 (see Appendix 3). As the SB1 button, you can use any of the microswitches listed in Appendix 1.

Rice. 39. Printed circuit board IR generator "business card"

Particular attention must be paid to the capacitor C5 permanently connected to the power supply, since if it is not chosen correctly, it may turn out to be the main energy consumer here. If the IR generator is small and powered, respectively, from a source of small capacity, then the leakage current in the capacitor C5 Ic5<1mkA. With small N, the capacitor C5 may have a smaller capacitance (and a smaller, respectively, Ic5). As a first approximation, you can take C5 (uF)"N.

The printed circuit board of the generator is made of double-sided foil fiberglass with a thickness of ~1,5 mm (Fig. 39). The foil on the side of the parts is used only as a neutral wire; to pass the conductors, it has selections-circles with a diameter of 1.5 ... 2 mm (not shown in the figure).

As a power source for the IR generator, you can take an 11A alkaline battery (Ж10,3x16 mm, Up=6 V, E=33 mAh). Note that in such devices, the electrical capacitance of the power source is not as important as its self-discharge, physical safety. The best of today's batteries - lithium - retain their performance up to 10 years.

*)Record NО{A} means that the element N belongs to the set {A}, i.e. can be one of the elements listed in it.

Publication: cxem.net

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