It may not be obvious why I chose that picture, but radio is all around us and we just don't notice it that much anymore. If you look at those buildings, every one of them has antennas on top.
So why doesn't your Robot have one? —Maybe you just need to understand how you can add radio to your 'bot.
Welcome to another "terribly exciting" installment in this short series on how to talk to your robot. This lesson will include sending and receiving radio–frequency signals by the addition of small "modular" circuits.
In the first schematic, you see an oscillator in the FM radio band. As long as we are not on the same frequency as any nearby commercial radio station, this is a good choice of band in which we can experiment. Why? –Because we can use a common FM radio to locate our signal. These circuits are not high quality circuits (Hi-Q), so we will end up with what might be called a "dirty" signal. Our circuit will not send out just one single frequency but rather it will send out one main signal plus several other side signals, called harmonics.
What you need to do is power up the transmitter circuit and turn on your FM radio. Look for the signal to be around 100 MHz. You will likely find more than one signal. Make sure the transmitter is at least 3 meters from the receiver, and try again. If you are far enough from the little transmitter circuit only the main signal will come through. The harmonics are much weaker.
Now that you know your transmitter is working, you can check the receiver. Let's use a circuit like the tone detector shown here. To check for signal let's temporarily put an LED between the +5v. supply and the output of the tone detector at the collector of the transistor. Now if you receive a signal, the LED should light up. The 3.6 KΩ resistor being parallel to the LED will not affect anything. Tune the receiver until the LED lights. If you have trouble with the frequency adjustment of either the transmitter or the receiver, you can spread the coils of inductor L ever so slightly, and check again for a good signal. (If the coil gets stretched out too much, you will need to compress it, and check again.)
(More to be added)