Television receiver remote control - uses two ultrasonic frequencies to avoid false switching by local interference

摘要

Two ultrasonic frequencies, F1 and F2 are used in this control system. In the transmitter, one of several switches can be operated which causes the main oscillator to be energised and F1 to be transmitted. After a time period, determined by the switch selected, an additional tuning condenser changes the oscillator frequency to F2. In the receiver, after receiving F1, a chain of pulses is triggered which operates a counter circuit. After receiving F2, the counter stops. The counter output is decoded and operates a remotely controlled circuit. This is suitable for television receiver control and is not susceptible to local interference.