Making Things Talk

WIRELESS COMMUNICATION 189

When you’ve got the microcontroller pro-

grammed, open the serial port that the receiver

is connected to using your serial terminal program,

at 2400 bits per second (thus far you’ve operated at

9600 or 19200 bps. For this example, just set your serial

terminal program to communicate at 2400 bps instead

of 9600). You might see a string of garbage characters.

That’s because the transmitter started sending before the

receiver was activated. Reset the microcontroller while

the serial port is open. After a few seconds, it should start

sending again, and you should see a string of numbers

representing the potentiometer’s value, like this:

127

128

128

129

130

129

You may also get garbage characters on the screen, even

when the transmitter is turned off. This is because the

receiver’s picking up random noise in its frequency range.

This can be generated by a wide range of sources. All elec-

trical devices emit some RF waves, so if your receiver is

sitting beside an LCD or CRT display, for example, it could

be picking up noise from that. In the absence of a signal

from the transmitter, the receiver will display anything it

gets. This is one of the downsides of working with simple

transmitter-receiver pairs like this: you need to filter out

the garbage in your program. More advanced transceivers

like the ones in the next example will do some or all of that

filtering for ...