How a TV Remote Control works

The IR Transmitter –TV remote:

Today’s modern remote controls work by modulating a infra-red LED. A series of pulses usually 10-20 pulses of varying width are sent to a gate that turns on or off, the modulator which is usually 37-40KHz. The reason for modulation is to separate the remote light from natural light. In the receiver there is a tone decoder, which responds well to whatever the remote is, 37-40KHz. The microprocessor decodes the series of pulses and determines whether it is valid and if it is, will respond to that function.

In late 1980s RC-5 protocol was developed by Philips as a semi-proprietary IR(infrared) remote control communication protocol for consumer electronics. However, it was also used by most European manufacturers, as well as many US manufacturers of specialty audio and video equipment. The other main protocol used by consumer electronics manufacturers is the NEC protocol. This protocol is largely used by Japanese manufacturers.

IR RECEIVER used at the TV end:

Description

A typical type is TSOP17 – series which are miniaturized receivers for infrared remote control systems are used inside the TV. The demodulated output signal from is directly be decoded by a microprocessor. TSOP1738 is the standard IR remote control receiver series, supporting all major transmission codes.

Features

• Photo detector and preamplifier in one package
• Internal filter for PCM frequency
• Improved shielding against electrical field disturbance
• TTL and CMOS compatibility
• Output active low
• Low power consumption
• High immunity against ambient light
• Continuous data transmission possible (up to 2400 bps)
• Suitable burst length .10 cycles/burst
• Carrier frequency should be close to center frequency of the band pass (e.g. 38kHz).
• Burst length should be 10 cycles/burst or longer.
• After each burst which is between 10 cycles and 70 cycles a gap time of at least 14 cycles is   necessary.
• For each burst which is longer than 1.8ms a corresponding gap time is necessary at some time in the data stream. This gap time should have at least same length as the burst.
• Up to 1400 short bursts per second can be received continuously. Some examples for suitable data format are: NEC Code, Toshiba Micom Format, Sharp Code, RC5 Code, RC6 Code, R–2000 Code, Sony Format (SIRCS). When a disturbance signal is applied to the TSOP17.It can still receive the data signal. However the sensitivity is reduced to that level that no unexpected pulses will occur. Some examples for such disturbance signals which are suppressed by the TSOP17 series are:
• DC light (e.g. from tungsten bulb or sunlight)
• Continuous signal at 38 kHz or at any other frequency