Although the RFM12B was designed for FSK (frequency-shift keying), it can also be used for OOK (on-off keying) transmissions. The trick is simply to turn its transmitter on and off via the SPI interface.
This can be used to control simple RF-controlled devices such as the FS20 power control units by Conrad and ELV in Germany. Here’s a sketch which turns a remote device (lamp, etc) on and off:
It turns out that the 868 MHz version of the RFM12B can even transmit 433 MHz signals, at least for simple OOK. The following example turns a device on and off via the low-cost KlikAanKlikUit units sold in the Netherlands, using the same 868 MHz radio module as above:
Both demo’s have been added to the RF12 source code library. Other slow-rate bit-stream protocols similar to the above could easily be added.
No attempt has been made to receive OOK signals right now, though one could imagine reading out the RSSI bit to determine the presence of a carrier…