a transistor + a couple of caps + resistor + a wire = a transmitter;
an active crystal oscillator controlled by your mcu pin + a wire = a transmitter;
a mcu pin flipping fast and furious + a wire = a transmitter;
I need a very small receiver. I can go upto about 8mm by 8mm. I only need it to toggle a small 3v motor on or off when it receives a signal. I'm not too woried about the size of the transmitter. Although the receiver will be less than 10Mtrs from the transmitter, it won't be possible to use IR as the receiver will be hidden when in use. Any suggestions?