Arduino 433Mhz RF link. Select a number to transmit (0-7) using the
dip switch on the transmit side. The press the button to transmit the
number. The receive side will then blink the onboard LED the received
number of times.
The 433Mhz RF link transmitter and receiver were purchased from
RobotShop.com
Circuit diagrams of the TX and RX circuits: