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When implementing a custom protocol, microcontrollers are typically the data source. A UART is a standard serial interface on most microcontrollers, so it is tempting to use them to output the protocol. However, UARTs do not work well for passing data over the air, their standard data structure and tight tolerances are designed for a wired system and they are not forgiving of the noise typically found in the RF environment. The best way of implementing the protocol is by bit banging a general purpose output. Bit banging involves setting the output high or low for the bit to be sent, waiting a bit time, and then setting the output for the next bit. The receiving microcontroller looks for the rising edge of the noise filter. It starts a clock on the edge and then stops it on the falling edge. If the time is within the specified window for the pulse, then the data is collected and conducts a logic filter check. One thing to note is that some radios constantly output data, most of which is random noise similar to the static on a TV when not tuned to a channel. When this continuous data is fed into the microcontroller it is constantly running, timing the pulses. This is a consideration for power consumption since the controller will not go to sleep in these cases.
