Making Things Talk

192 MAKING THINGS TALK

Radio Transceivers

In many cases, one-way communication isn’t enough. For example, you might have

noticed in the previous example that sometimes the message doesn’t get through,

even when you’ve got the circuitry and the code fully working. In that case, you might

want the PC to be able to query the microcontroller occasionally to see the state of

the inputs. Or perhaps you’re making an application in which there’s input and output

on both sides. In that case, transceivers are essential.

There are many different kinds of data transceivers on

the market. Some connect directly to the serial I/O of the

microcontroller and send the data as is. Some, like the

Bluetooth module you saw in Chapter 2, add an additional

protocol layer on top of the data communication, so you

have to be able to implement that protocol on both sender

and receiver. The cost of transceivers varies widely.

Until recently, most digital radio transceivers on the

market implemented only the most basic serial com-

munications protocol. For example, the RTF-DATA-SAW

transceivers from Abacom do a good job of sending and

receiving serial information. They connect directly to the

serial transmit and receive pins of your microcontroller.

Any serial data that you send out the transmit line goes

directly out as a radio signal. Any pulses received by the

transceiver are sent into your microcontroller’s ...