This short tutorial is a discussion of the implementation of serial communication via RF for my final project. Rather than communicate using the radio side of the project board, I purchased and integrated RF modules from Linx Technologies: these are low-cost, pre-tuned receivers and transmitters that make it easy to add RF capability to a device with a microprocessor. Linx offers several models, including those that take/give a transmission-encoded stream as input/output, and those with built-in encoders and decoders for direct expression of transmitted bits on their output pins.

I started by building two instances of the PIC project board, and attached Linx KH series components to enable RF communication at 418 MHz. The KH series components are receivers and transmitters with built-in encoders and decoders; hence, one can express a direct bitstream at the inputs of the transmitter and receive the same bitstream at the output pins. Hence, digital sensors could be connected directly to the modules. Each chip acceptance of 8 parallel data bitstreams, so multiple devices can be linked to one transmitter or receiver. With the KX chips, one matches receiver/transmitter pairs by specifying 10 tri-state address bits on the receiver and transmitter. Hence, one can multiplex one entity to multiple opposites by actuating the address bits using a PIC, and then listening for the specific transmission.

See the data sheets for the KH components: KH transmitter data sheet, KH receiver data sheet.

And a list of other Linx receiver/transmitter pairs: http://www.linxtechnologies.com/ldocs/f_prod.html.

Here are circuit diagrams for the PIC-RF connections. RF transmitter board circuit diagram; RF receiver board circuit diagram. Note that the transmitter can take 5V Vcc from the project board, but receiver requires a ~3.3V, which is achieved by placing a 200 Ohm resistor between the power pin and Vcc at 5V.

For all other connections to the PIC, refer to Matt Reynolds' documentation for the project board: http://www.media.mit.edu/physics/pedagogy/fab/micros/MAS863picproject.pdf

Linx Technologies: http://www.linxtechnologies.com/

Wireless Design and Development, trade magazine for wireless communications technology: http://www.wirelessdesignmag.com/scripts/default.asp

A variety of links to PIC programming and networking sites: http://www.dontronics.com/piclinks.html