Infra-red remote control

EE December 1986 INFRA-RED REMOTE CONTROL With the ready availability of infra-red emitters and sensors at very reasonable prices, it has become possible to construct remote control units for operating garage doors, hi-fi sets, and light switches, to name but a few The proposed remote control system is based on a four-channel infra-red (IR) transmitter and associated re- ceiver. A block schematic of the system is shown in Fig. 1. In essence, the transmitter is a four- channel CW (continuous wave) type; each key on the control keypad pro- duces a specific carrier frequency for a fixed duration. In the receiver, a phase-locked loop (PLL), dimensioned for one specific transmitter channel detects the car- rier and activates the output cir- cuitry, i.e. a LED for visual feedback and a relay which switches the mains load. Note that the receiver will only respond to one of four possible transmitter channels; therefore, each load to be controlled requires its own receiver. As there are re...