IR TV Remote Transmitter
This page describes Infrared(IR) TV remote transmitter basics. It also mentions IR TV remote receiver. As we know every electronic item available is being sold with remote control. Electronic products such as VCRs, TV, CD player, stereo system, Table FAN are sold with remote controls.
Remote control is a handheld device with battery. It converts user entry into serial digital code which is transmitted over infrared beam to the other part of the system i.e. receiver. The receiver receives the IR beam which is converted back to the codes and based on codes specific action is performed at the receiver end.
Let us understand IR TV remote. The major functions performed by such remote control device are volume control and TV channel selection. There are other functions also performed by such remote devices.
Fig-1 describes IR TV remote transmitter. It consists of keyboard, IR LED driver transistors and IC housing other functionalities. Typically remote keyboard will have 8 rows and 4 columns and houses SPST push button switches. The keyboard is connected to the encoder IC. The encoder circuit converts input user entry into unique binary code. Encoder generates code of size 6 bits and few generates 32 bits. The remotes are available which generates 9 and 10 bits also.
Fig.1 IR TV remote transmitter
The standard NRZ code is generated. The typical bit rate is 30 to 70 kbps. This serial data bit stream makes higher frequency pulse on or off according to binary code 1 or 0.
The IR TV remote transmitter houses clock oscillator which runs at 455KHz using external mounted ceramic resonator. The serial binary data make this 455 KHz pulses ON or OFF. IR source can be one or more IR LEDs as shown so that signal with sufficient power level is reached at the receiver part.
Fig.2 Pulse waveforms used by IR TV remote
As shown in fig.2 , a binary 1 generates pulse of 16 , 455 KHz pulses while at the binary 0 positions no pulses are being transmitted. The fig.2 depicts 6 bit code with the start pulse. The code in this example is 011001. The period T of 455KHz pulses is 2.2 µs. Hence 16 pulses will occupy 35.2 µs. This results into code bit rate of 1/(35.2X10-6 ) or 28.410 KHz.
IR TV Remote receiver
Fig.3 depicts IR TV remote receiver modules. As shown IR photodiode is placed at the front end. The received signal is very small in magnitude. Hence two or more high gain amplifiers are provided to boost the level using AGC. The incoming data pulses are detected and shaped using detector and wace shaper. They are converted into original serial data stream.
Fig.3 IR TV remote receiver
The data is read by the processor and action such as channel selection or volume control is performed accordingly. The other functions such as brightness, contrast and sleep timer etc. are also available.
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