RC-5

RC-5 is a protocol for transmitting data via infrared interface and is used in particular in infrared remote controls of TV or audio equipment. The code was developed in the late 1980s by Philips.

Construction

The serial data bits are combined into a frame and transmitted at a carrier frequency of 36 kHz by means of Manchester code. The frame to 14 bits consists of:

  • A start bit that always is logic 1 and enables the receiver to select the proper gain for the following data bits.
  • A Field - bit which is used to distinguish between a lower command area with a range of values ​​from 0 to 63 and an upper command area with a range 64-127.
  • A control bit on the remote control changes its state at every keystroke. Therefore one can distinguish between the permanent press and hold a key and the repeated pressing and releasing.
  • One 5 -bit address system to choose between 32 different types of equipment.
  • A 6 -bit command value which is a function of a set of 64 possibilities (or in combination with the Field -bit 128) selects. Each function, such as the adjustment of the volume, while a particular command value is assigned.

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

Modulation

Often manchester encoded data with a rectangular carrier with approximately 35 to 40 kHz are modulated. Here, the "idle " state, that is, the logical value of which is taken before and after the transmission, nothing is sent ( minimal to no amplitude). For the other logical value the square wave signal is transmitted with maximum amplitude. Thanks to this modulation, the receiver, the signal using a high -pass filter from the noise of the ambient light differ (especially network oscillations at 50 Hz, which are produced by many lights ). To simplify keep the electronics in the receiver to an integrated circuit ( IC) manufacturers use since the 1990s, mostly in a colored plastic housing, which greatly reduces non- infrared light. The device includes a photo detector, a controlled amplifier and a demodulation circuit. At the output of the digital Manchester code is at, which was modulated at the beginning in the remote control.