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    Infrared remote control signal transmission and reception


    We have said that by pressing the remote control button on the remote control color TV can be a series of remote control operation, in fact, press the button on the remote control and press the single-chip computer matrix button in a button is essentially nothing Different, they are to the single-chip computer input coding pulse, the difference is that the remote control input to the single-chip computer coding pulse must first be modulated into infrared radiation out, and then processed by the infrared receiver circuit to the remote control system in the single Computer. The following describes the basic principles of infrared remote control launch and reception.
    (A) the principle of infrared remote control launch
    The Block Diagram of Infrared Remote Control Transmitter. It consists of a key matrix, a key encoder, an instruction encoder, a modulator, a buffer amplifier, a scan generator, a clock pulse generator oscillator, an exciter, and an infrared emitting diode. Which key encoders, instructions
    The encoder, the modulator, the buffer amplifier, the scan generator, the clock pulse generator, the oscillators are integrated in the integrated circuit, the patch is mounted on the printed circuit board of the hand-held transmitter, the key matrix circuit and the integrated circuit internal key And the scanning generator is connected with the scanning generator. The working principle of this part circuit is the same as that of the single-chip computer's external key matrix circuit in the remote control system. When the input and output intersections are shorted, the key value corresponding to the key to be pressed will enter the input of the key encoder, and the key value is entered in the key encoder to identify the key bit What command the user has issued to the remote control system).
    Oscillator oscillation frequency by the external ceramic crystal oscillator Zo1 decision, usually Z01 resonant frequency of 455kHz or 48okHz. The oscillation signal all the way through the clock pulse generator frequency, strobe, the clock pulse and about 38kHz carrier frequency signal. Clock pulses sent to the instruction encoder and scan generator, carrier frequency signal sent to the modulator. The command code output from the instruction encoder is modulated on the carrier signal. This signal is amplified by the internal buffer amplifier of the integrated circuit and sent out from the integrated circuit to the excitation amplifier circuit of the infrared emission diode. In the handheld infrared remote control transmitter, the oscillation frequency of the oscillator is about 455kHz, it is close to the semiconductor superheterodyne radio IF, so according to the principle of electromagnetic radiation to determine whether the infrared transmitter oscillator circuit is working properly. The specific approach is to turn on the radio, the band is set in the wave, and set it to the low-end reception frequency (for example, 550kHz), the remote control transmitter near the radio antenna, press the remote control any button, if the radio is loud The alarm is a ceramic crystal bad, or integrated circuit is bad, maintenance is usually the first change, the first time the battery is not the same as the radio, Ceramic crystal, if the fault is still, and then replace the integrated circuit, because the IC is the use of patch technology welding on the printed circuit board, so replace the Ic is actually replace the entire remote control transmitter circuit board. The output signal from the IC output has been sent to the transistor composed of elements such as infrared light-emitting diode excitation drive amplifier, driven by the transistor V101 amplified output to control the flow to the infrared light-emitting transistor V102. When V102 has a forward current flow, the outward radiation is about 932nm infrared is not visible. Infrared light-emitting diode installed in the remote control of the front, shape, with the diode is basically the same positive and negative characteristics, amateur conditions with 47-type multimeter R × 1k block to measure the reverse resistance is infinite, forward resistance of about 30k ohm Gamma. The
    (B) the principle of infrared remote control reception
    Infrared remote control receiver circuit, as the name suggests is able to receive infrared light signal circuit, therefore, this circuit requires a photoelectric conversion device - infrared light-emitting diode photodiode. It is composed of preamplifier integrated circuit infrared remote control receiver circuit. At present, the most commonly used preamplifier integrated circuits for the CX20106A and Hiroshi PC1373H, they are optoelectronic receiver preamplifier.
    A schematic block diagram of infrared remote control receiver circuit composed of infrared photodiode and photoelectric preamplifier. Preamplifier, automatic level control, limiting amplifier, peak detection, waveform shaping circuits are integrated in the circuit. When there is no infrared light, the infrared receiver diode is almost no reverse bias current, the integrated circuit is not output when there is infrared radiation, V, produce photocurrent, amplified by the preamplifier, limiting circuit limit to eliminate interference, and then by peak detection Detect the modulation signal, and finally after the waveform shaping circuit output, sent to the single-chip computer remote control instruction code input port. In the photoelectric preamplifier, the preamplifier has an automatic level control in order to accommodate the same sensitivity of the infrared remote control within a specified distance range. When the remote control, the preamplifier gain down to prevent the circuit saturation distortion caused by remote control failure. As the photodiode by the infrared excitation of the light current is very weak, so the requirements of the photoelectric preamplifier has a high gain. In order to prevent the interference of external spurious electromagnetic waves, the process of the photodiode, photoelectric preamplifier package in the 3 × 3X1.3cm 3 or so metal shielding box, the front of the box with a photodiode location with a mesh window, The purpose is to transmit infrared light, the entire shielding box installed in close proximity to the TV front panel position. When a remote control color TV has a low remote control sensitivity, it is not necessary to remove the metal shielding box or remove the mesh window in order to increase the window area of the transmitted infrared light. This does not increase the remote control sensitivity, but instead increases the interference due to interference So that remote control sensitivity is lower. Usually cause remote control low sensitivity for the remote control transmitter bad or remote control infrared receiver circuit is not working properly.
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