I finally got some small 433MHz radio transmitters and receivers and I needed an encoder/decoder circuit to make use of them for controlling equipment remotely. One could realize this by using Motorola MC145026-8 integrated circuits as well, but they need space and a few external components that must be calibrated by the user.
The encoder/decoder parts are to be connected to a transmitter/receiver module which takes care of the transmission of digital signals by radio or infra waves. The communication signal format is designed to be used for radio transmission (it has a constant 50% signal/silence ratio), but it can work with infrared devices as well. The transmitter has a varying number of buttons and sends the states of these inputs to the receiver. The receiver device decodes the message and sets the outputs accordingly. There are two protocols in the sources: the older version V2 represents digital 0 and 1 as different frequency pulses (800 and 1600 Hz), while the newer V4.0 outputs standard Manchester code (400/800 Hz). I recommend using the Manchester versions as the max. generated frequency is lower and the reception is more stable even with low speed or timing-inaccurate transmission channels.
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