RC-5

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RC-5 is a network protocol for data transmission via an infrared interface and is used in particular for infrared remote controls for televisions or audio devices. The code was developed by Philips in the late 1980s .

construction

The serial data bits are combined into a frame and transmitted using Manchester code on a carrier frequency of 36 kHz. The 14-bit frame consists of:

  • A start bit that is always logical 1 and allows the receiver to select the correct gain for the subsequent data bits.
  • A field bit that is used to differentiate between a lower command area with a value range from 0 to 63 and an upper command area with a value range from 64 to 127.
  • A control bit that changes its state each time a button is pressed on the remote control. This allows a distinction to be made between the permanent holding of a key and the repeated pressing and releasing.
  • A 5-bit system address to choose between 32 different device types.
  • A 6-bit long command value that selects a function from a set of 64 options (or in combination with the field bit 128). A specific command value is assigned to each function, such as adjusting the volume.

The duration of each bit sent is 1.778 ms, the 14 bits of a frame require 24.889 ms for transmission. The data frame is repeated every 113.778 ms when the button is pressed.

modulation

Comparison of modulated (above) and demodulated signal (address = 20, command = 13, toggle = 0) transferred word: 110 10 100 001 101 (falling edge = 1)

The square carrier generated with a 144 kHz generator is coded using Manchester code and, due to its frequency, has transmission pulses of 6.9444 µs (1 second / 144 kHz = 1 cycle). In order that a signal modulated with 36 kHz can be generated (1 second / (pulse duration + pause duration) = 36 kHz), the pauses must be 20.8332 µs (= 3 cycles) long. Nothing is sent for the "idle" state, that is, the logical value that is taken before and after the transmission (minimal to no amplitude ). For the other logical value, the square-wave signal is sent with maximum amplitude. Thanks to this modulation, the receiver can use a high-pass filter to differentiate the signal from the noise of the ambient light (especially mains oscillations at 50 Hz, which are generated by many lights). In order to keep the electronics in the receiver as simple as possible, manufacturers have mostly been using an integrated circuit ( IC ) in a colored plastic housing since the 1990s , which greatly reduces non-infrared light. The component contains a photodetector , a regulated amplifier and a demodulation circuit . The digital Manchester code is available at the output, which was initially modulated in the remote control.

Individual evidence

  1. ↑ Philips Semiconductors: Remote Control System RC-5 Including Command Tables , December 1992, publication number: 9388 706 23011
  2. ↑ buyer: RC5 - remote control code. In: www.opendcc.de. Retrieved January 6, 2017 .

literature

Web links