[Infrared] principle of infrared remote control, infrared remote control

[Infrared] principle of infrared remote control, infrared remote control

Abstract:
The infrared remote control device has the characteristics of small size, low power consumption, strong functions, and low cost. Therefore, after the color TV sets and video recorders, infrared Remote Control has also been adopted on recorders, sound equipment, air litter machines, toys, and other small electrical devices. In industrial equipment, infrared remote control is completely reliable and can effectively isolate electrical interference in environments such as high voltage, radiation, toxic gases, and dust. This article focuses on

Keywords: infrared, remote control, decoding, encoding

1. Overview

The infrared remote control system consists of the transmitting part and the receiving part, and uses a dedicated IC chip for editing/decoding to control the operation, as shown in figure 1. The transmitting part includes the keyboard matrix, encoding modulation, and LED infrared transmitter. The receiving part includes the optical/electrical conversion amplifier, demodulation, and decoding circuit.

Figure 1 Infrared Remote Control System

2. encoding format

(1) Bit definition:

As shown in 2, "0" and "1" are represented by the same high width and different low width respectively (the receiving end is the front low and back high ):
1. "0": the binary "0" is represented by a combination of 0.565 ms (pulse width), 0.56 ms (interval), and ms (cycle).
2. Representation of "1": the binary "1" is represented by a combination of 0.565 ms (pulse width), 1.685 ms (interval), and ms (cycle ".

Figure 2 a transmitter encoding "0" and "1"

Figure 2 B receiver encoding "0" and "1" (opposite to transmitter level)

(2) Encoding

The binary code consisting of "0" and "1" is modulated twice with a carrier frequency of 38 kHz to improve the transmission efficiency and reduce power consumption. Then, infrared emission diodes are used to generate infrared emission into space.

Currently, most remote controls on the market use the 32-bit encoding method. The 32-bit remote control code is a continuous 32-bit binary code group: the first 16 digits are user identification codes (different electrical equipment, to prevent remote control codes of different types from interfering with each other). The last 16 bits are 8 bits (function codes) and Their Reverse codes (used to check whether the data is accurate ).

When a key is pressed for over 36 ms, the oscillator activates the chip and will emit a set of encoded pulses of milliseconds, which transmit code from a boot code (9 ms ), one result code (4.5 ms) with a low 8-bit address code (9 ms ~ 18 ms), 8-bit high address code (9 ms ~ 18 ms), 8-bit data code (9 ms ~ 18 ms) and the 8-bit data back code (9 ms ~ 18 ms), as shown in 3. If the key press exceeds limit ms, the code to be sent will only consist of the Start code (9 ms) and end code (2.25 ms), as shown in figure 4.

Figure 3 remote control signal coding Waveform

Figure 4 waveform of remote control bursts of Signals

Figure 5 guide code figure 6 send code

(3) code width calculation:

Minimum 16-bit address code width: 1.12 × 16 = 18 ms;
Maximum 16-bit address code width: 2.24ms × 16 = 36 ms.
The width of the Eight-bit data code and its eight-bit anti-Code remain unchanged: (1.12 ms + 2.24 ms) × 8 = 27 ms
The width of the callback 32-bit code is (18 ms + 27 ms )~ (36 ms + 27 ms)

3. remote signal reception

The receiving circuit can use an integrated infrared receiver that combines infrared reception and amplification without any external components, it can complete all the work from the infrared to the output compatible with the TTL level signal, and the size is the same as that of the common plastic transistor, it is suitable for a variety of infrared remote control and infrared data transmission.

The receiver has only three external pins: Out, GND, Vcc, and single-chip microcomputer interface, as shown in figure 7.

Figure 7 infrared receiver
① Pulse signal output is connected directly to the single chip microcomputer IO port.
② Ground line of the GND System (0 V );
③ Power Supply positive pole (+ 5 V) of the Vcc system );

4. Decoding

The key to decoding is how to identify "0" and "1". From the bit definition, we can find that "0" and "1" both start at a low level of 0.56ms, the difference is that the width of the high level is different, "0" is 0.56 ms, "1" is 1.685 ms, so the difference must be based on the width of the High Level "0" and "1 ". If it is extended by 0.56 ms after the 0.56ms low level, if the read level is low, it indicates that this bit is "0", and vice versa is "1", for the sake of reliability, the latency must be longer than 0.56ms, but cannot exceed 1.12 ms (2*0.56 ms). Otherwise, if the bit is "0", it is the lower level of the next bit, therefore, (1.12 ms + 0.56 ms)/2 = 0.84ms is the most reliable, generally around ms.

According to the code format, you should wait for the starting code (low level) of 9 ms and the result code (high level) of 4.5ms to complete before reading the code.

What is the principle of infrared remote control? The remote control is actually the radio transmitter. when the key is pressed, the chip in the key will press the control area on the circuit board to send the infrared rays to the receiver for receiving, so that the remote control is triggered by each key and the infrared wavelength sample is sent to realize the key (or multi-key combination) control thing happening
As for the use of infrared because the infrared wavelength is long, large objects that touch the size can be diffraction, so as to bypass the obstacle to implement remote control
Infrared Remote Control Circuit Diagram net write simple infrared remote control

Point: Figure 2-97, 2-98 ...... View chart
Go to http://www.leyuandz.com/farc/zuijiandanhongwaifasheqi.asp.

Figure 2-97 circuit diagram of an infrared transmitter consists of a few components. The output frequency of a Multi-harmonic oscillator circuit is controlled by R2 (Ω resistor adjustment ).

The duty cycle of the output signal is about. In other words, the turn-on time of the infrared emission diode is about equal to the turn-off time.

The resistance R4 controls the output current of the PH303 emitting diode and slightly adjusts the current below 100mA because the PH303 diode has 50% power-off time.

Average diode current less than 50mA

Figure 2-98 receiver circuit diagram PH302 infrared receiver diode reverse bias mode working by R1 provide reverse bias normally flows through PH302

The current is only weak. The current pulse flows through this circuit every time it receives the infrared radiation pulse from the transmitter.

A small voltage pulse is generated at the junction of R1 and PH302, coupled by C2 to the input of the first-level amplifier.

In fact, when the distance and range of the remote control system are close to the large limit, the voltage pulse is almost at the peak to the peak (Vp-p) value is less than 1mV, so it needs to be quite large.

The signal level is raised to the control relay level only after the magnification.

All of them belong to the common shot amplifier, VT1, VT2, and VT3 which provide voltage gain of over 40 dB. VT2 only has low gain because R0 introduces negative loop.

The signal is amplified by VT2 and the output signal is rectified by the diode VD1 and VD2, And the DC (DC) signal is generated by the C5 smoothing to enable the VT3 to be turned on.

When selecting components, the key infrared emission and receiving diode emission tubes PH303 have two specifications: narrow angle and wide angle infrared emission diodes refer to their tubes.

When the core is made, the angle of the reflection cone (parabolic) is small, and the distance from the strong direction is also far; otherwise, the distance from the wide (WIDE) angle infrared emission diode is also far.

Relatively large area

The component is selected as shown in the following figure:

Debugging is relatively simple, two machines are powered at the same time, press the transmitter control switch S key circuit starting vibration work fine-tuning R2 resistor at the same time PH303 roughly to the receiver

When the direction of the PH302 receiving tube is adjusted to R2, the sound-absorbing line is listened to by the relay. Because the receiver has no special requirements on the transmitting frequency, the R2.

Relay

The remote control distance between the two devices is greater than 8 m and less than 30 degrees when a narrow-angle infrared transmitting tube is used.

This remote control uses children's toys, camera shutter remote control, Home Appliance Remote control, and other shortcomings. Poor stability is easily affected by its continuous light source.