GB1376387A - Automatic tuning circuit - Google Patents

Abstract

1376387 Touch responsive switching systems SABA SCHWARZWALDER APPARATE -BAU-ANSTALT AUGUST SCHWER SOHNE GmbH 18 Dec 1972 [17 Dec 1971] 58281/72 Heading G1N [Also in Division H3] In an automatic tuning circuit for a receiver in which capacitance diodes are used for tuning and the tuning voltage UT is obtained by charging and discharging a capacitor 15 via two constant current means 13, 14, the charging and discharging action by means of a respective bi-stable 9, 10 is automatically interrupted on reaching a received signal 27 and the existing charge is retained by a fine tuning voltage 28, and tuning is effected by touching an electrode 1, 2. Touching an electrode 1, 2 suppresses an oscillator 3, 4 such that brief touching initiates automatic tuning by producing an impulse through a capacitor 7, 8 to set an associated bi-stable 9, 10 whereas a longer period of touching the electrode causes a time constant circuit 17, 18 to be switched in after a predetermined delay to se the associated bi-stable 9, 10 and cause continuous tuning which is interrupted after releasing touching the electrode by a reset impulse to the bi-stable derived from a received signal 27. To avoid accidentally initiating continuous tuning operation due to successively touching the electrode 1, 2 a capacitor 23, 24 is discharged in the intervals between touching the electrode via a diode 21, 22 and a transistor 5, 6. The bi-stable 9 or 10 set by a brief or a larger touching of the electrode 1 or 2 causes the capacitor 15 to charge or discharge via current source 14 or current drain 13 until a received signal is obtained at 27 to reset the bi-stable 9 or 10. The tuning voltage UT is then maintained by the fine tuning voltage obtained at 28 via the FET 16. When the electrode 1 or 2 is touched for the longer period the suppression of oscillation at 3 or 4 turns off the transistor 5 or 6, after 1-5 seconds capacitor 23, 24 has charged sufficiently and the circuit 17 or 18 operates to set the bi-stable 9 and 10 to provide continuous tuning. The diodes 25 and 26 are provided to reset the bi-stables 9, 10 when the tuning voltage UT reaches an upper or lower limit.