Patent GB-1219557-A (GB)
Title: Single wire control system
IPC: H03F3/195
Filed: 1969-08-18
Abstract: 1,219,557. Remote control systems. FORD MOTOR CO. Ltd. 18 Aug., 1969 [9 Sept., 1968], No. 41084/69. Heading G4H. A single-wire control system for selectively actuating a plurality of remote switches 134, 136, e.g. in a motor vehicle, comprises an electronic oscillator connected to each switch and near it, the switch being actuated when the oscillator is oscillating, each oscillator working at a different frequency and having a feedback loop from output to input and an input transistor connected to the control wire 38 and adapted to turn off the oscillator when the resistance to the oscillator frequency presented by the control wire is high, the control wire being connected to a control module 24 having a manual switch 30, 32 for selectively reducing the impedance to earth at each oscillator frequency to turn on the corresponding oscillator. Components 40, 42 to be controlled have adjacent transistor amplifiers 44, 46 formed as integrated circuits (Fig. 2, not shown). The output terminal 8 of amplifier 44 is connected by a resistor 94 to terminal 98 and a piezoelectric crystal 102 connects terminal 98 via line 106 and capacitor 110 to the input terminal 1. Terminal 98 is connected to earth via resistor 114 and lead 106 is connected to earth via resistor 118 and crystal 122. The supply lead 22 from battery 20 is connected to the anodes of diode 130 connected via power transistor 134 to the component 40. The base of transistor 134 is connected via resistor 138 to the collector of transistor 142, the emitter of which is connected via resistor 150 to earth. Terminal 6 of the amplifier is connected to the base of transistor 142 and via resistor 154 and capacitor 156 to earth. The amplification of amplifier 44 is determined by feedback resistor 90 and the frequency of oscillation by crystal 102. The corresponding crystal 34 in the control module has the same operating frequency. Other operating frequencies differ by at least 4%. Inductor 26 in the control module passes to earth any D.C. voltage on lead 38 but presents a high impedance to the A.C. signals. When switch 30 is open there is a high A.C. impedance between the amplifier 44 and earth. The amplifier then has a low gain and the oscillator is quiescent; transistors 142 and 134 are non-conducting. To operate component 40 switch 30 is closed so that the amplifier 44 has a high gain and oscillation starts. The oscillations on feedback loop 106 are rectified by a diode in the amplifier unit 44 to give a D.C. bias on lead 6 causing transistor 142 to conduct and turn on the transistor 134, applying the battery voltage to the component 40. There may be another control module 24<SP>1</SP> having a switch 176 and a crystal 34<SP>1</SP> and performing the same function as switch 30 and crystal 34. In another form (Fig. 3, not shown) amplifier 44 has three feedback loops with crystals of different operating frequencies. The control module contains three switches with three corresponding crystals. When one of the switches is closed the amplifier oscillates at the corresponding frequency due to the corresponding crystal in one of the feedback loops. The signal in this loop is rectified to give an output on one of three leads. This system may, for example, be used to operate the heater blower motor at three different speeds.