Patent GB-1283543-A (GB)
Title: A tuning indication circuit operating device
IPC: H03K17/96
Filed: 1969-08-18
Abstract: 1283543 Automatic frequency control; touch operated switches; tuning indication MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 18 Aug 1969 [22 Aug 1968 24 Oct 1968 30 Oct 1968 (2) 13 Nov 1968 18 Nov 1968 26 Dec 1968 27 Feb 1969 (2) 23 May 1969 25 June 1969] 41202/69 Headings H3A H3B and H3Q A tuning indicator circuit for television utilizes the capacitance of a human body to operate a switch controlling its operation. A switch 12 in the form of a pair of arcuate electrodes mounted on a tuning knob, Fig. 1 (not shown), is connected in shunt across the input of a switch comprising transistors 21, 22. If the switch 12 is touched by the hand the high frequency supply from oscillator 11 is shunted by the capacitance of the human body to earth so that transistors 71, 21 become non-conductive and the supply + B2 is impressed on the tuning indicator circuit 23 to operate it. Tuning is then carried out by rotating the knob of switch 12. When the hand is removed from switch 12 the latter is open so that the 3À85 Mc/s. signal is applied to transistor 17 to render it and hence transistor 21 conductive to render the tuning indicator circuit non- operative. Transistor 17 may be replaced by a diode detector and a smoothing circuit, Fig. 5 (not shown). An inductor may be connected in parallel with the switch 18 to form a circuit resonant at the 3À85 Mc/s. frequency when the switch is not touched to increase the speed of switching, Fig. 6 (not shown). The high frequency oscillator 11 may be the horizontal line time base valve, Fig. 7 (not shown). In order to prevent leakage of the high frequency signal through the human body when the switch 12 is touched which would produce unwanted radiation transistor 17 is replaced by a diode detector, smoothing arrangement, switch 12 is placed between the winding 15 and capacitor 16, a resistor is connected in shunt across the switch 12 and a diode is connected in series between the winding and capacitor, Fig. 8 (not shown). The arrangement is such that only a D.C. voltage appears across the switch 12 when it is touched. Alternatively Fig. 9 (not shown) a voltage doubler may be connected between capacitor 16 and transistor 17 and a capacitor connected in series and one in shunt with the switch 12. By connecting a parallel circuit resonant at the supply frequency in shunt across the transistor switch, Fig. 10 (not shown), activation of the circuit by extraneous signals coming in through the body may be avoided. A.F.C. circuit, Fig. 12.-When switch 61 is not touched, i.e. is open, transistor 67 is rendered conductive by the 3À85 Me signal from oscillator 55 resulting in zero voltage being applied to tuning indicator circuit 59 to render the latter inoperative. At the same time transistor 71 does not conduct so that a voltage is applied to the collector of transistor 73 to render it conductive and thus allow an A.F.C. signal to be obtained from terminal 93, an I.F. signal being applied to terminal 74 and thence via detector circuit 84, 85, 86, 87 and 88 to transistor 73. When switch 61 is touched the 3À85 Me signal is shunted to earth and transistor 67 rendered non- conductive so that the supply voltage +B is impressed on the timing indicator circuit 59 to render it operative and transistor 71 conductive so that transistor 73 conducts and no A.F.C. signal is derived on terminal 93 during the period of tuning. Waveband switching, Fig. 13.-A touch capacitance switch 100 is provided in the local oscillation frequency adjusting knob of the U.H.F. tuner and is operated when the operator touches the knob to rotate it. If a U.H.F. broadcast is being received as shown with the changeover switch 109 in the position shown then when the switch 100 is not touched transistors 101, 102 conduct due to the signal from oscillator 96 and control circuit 119 of the tuning circuit is de-energized. When the switch 100 is touched transistors 101, 102 are rendered non- conductive and the control circuit 103 energized. With the changeover switch in the position shown the voltage developed at d is substantially zero so that transistor 101 is controlled solely by the touching of switch 100. If the switch 109 were set so that a V.H.F. broadcast was being received then a voltage of about 10V is obtained at d which renders transistor 101 conductive and the control circuit 103 is de-energized independantly of whether or not switch 100 is touched. In order to achieve V.H.F. tuning switch 105 has to be turned on to render transistor 101 non-conductive. In order to prevent the switching circuit from being erroneously actuated due to a change in the power source voltage a voltage dependent upon the power source voltage is applied to the switching circuit as a bias voltage, Figs. 15, 17 (not shown).