Patent GB-1307563-A (GB)
Title: Control systems responsive to remotely transmitted acoustic control  signals
IPC: H04N5/44
Filed: 1970-05-08
Abstract: 1307563 Controlling by sound; selective signalling RCA CORPORATION 8 May 1970 [14 May 1969] 22475/70 Headings G4F and G4H [Also in Division H3] In a remote control system, a receiving means 14, 36, 22 provides corresponding electrical signals in response to remotely transmitted acoustic control signals, control circuits 26 for controlling functions of apparatus are coupled to the receiving means 14, 36, 22, a detector circuit 30, 34, 50 is coupled to the receiving means for detecting spurious amplitude variations of signals and a switching circuit 52 is connected across the output of the receiving means and is responsive to the detector circuit when the signals of spurious amplitude variation are detected for by-passing the electrical signals for inhibiting erroneous operation of the apparatus functions by the signals having the spurious amplitude variations. As shown the transmitter 10 which may be hand held, includes a transistor oscillator which is actuated by pressing a button to produce one of eight ultrasonic control frequencies which is transmitted by a sonic transducer. With no input signal transistor 36 is saturated. When a sound signal is received by microphone 12 and amplified by amplifier 14 the negative half cycles cut off transistor 36 causing the inductance 20 and capacitance of a voltage dependent resistor 28 to ring. One positive polarity output pulse is developed across the ringing circuit 20, 28 for each cycle of the signal applied to the transistor 36 as the negative portions of the ringing signal are attenuated by the conduction of the collector-base junction of the transistor 36. The first several positive going ringing pulses are attenuated by a low impedance path comprising resistor 21, diode 23 and capacitors 19 and 34 charging capacitor 19. The periodic non-conduction of the transistor 36 causes the average current through the resistor 30 to decrease and the voltage at 42 to increase to a positive value at a rate determined by RC 30 and 34. This transient increase in voltage at 42 causes diode 50 to conduct and charge capacitor 54. When the capacitor 54 has charged sufficiently positive transistor 52 conducts and discharges capacitor 19 and shunts the positive going ringing pulses to ground. When the positive going transient at 42 becomes less steep, the diode 50 becomes non-conductive and transistor 52 turns off. Then the ringing pulses across the primary 20 are attenuated by the circuit including diode 23 until capacitor 19 is charged. After the delay such as 100 ms. provided by the above operation the ringing pulses are passed from the secondary winding 24 for application to the control circuits 26 of the T.V. receiver. The voltage dependent resistor 28 prevents spike voltages from developing across winding 20 which may cause breakdown of the transistor 36. Spurious signals may contain other frequencies as well as ones close to the desired control channel and the non-linear interaction of the various components of the spurious signals produce beat frequencies of lower frequency. Consequently the repetition rate at which transistor 36 is turned off is modulated by these lower beat frequencies. However, the time constant of resistor 30 and capacitor 34 produces signals which are detected by diode 50 and are used to turn on transistor 52 so that ringing pulses developed across the primary winding 20 are attenuated to prevent the spurious signals from falsely actuating the control circuits 26.