| 摘要 |
1,033,458. Transistor circuits. SONUS CORPORATION. April 28, 1965 [April 28, 1964], No. 17948/65. Heading H3T. [Also in Division G4] A swimming pool monitor may be switched from an alarm " A " condition in which disturbances in the pool actuate an acoustic alarm, to a monitor " L " condition in which sounds in the vicinity of the pool may be monitored. In the " A condition, switches 54a, 54b restrict the bandwidth of amplifier 12 to a range of 500-900 cycles extending upwardly from 2500 c/s. Sounds from hydrophone 10 are amplified by amplifier 12, and the negativegoing half-cycles of the output signal are passed by diode 70 to switch a bi-stable circuit 76, 92 to the state in which transistor 92 conducts. When transistor 92 conducts relay 100 operates, closing contact 100a to apply H.T. to transistor 112. Switch 54e completes a positive feedback path between transistors 122 and 112, and on the closing of contact 100a this circuit oscillates to produce an output at speaker 120. The alarm signal persists until cancelled by switch 94. In the " L condition, switches 54a, 54b connect larger capacitors in circuit, and the amplifier 12 passes all speech frequencies. Switch 54e breaks the positive feedback path and transistors 112, 122 form a further twostage amplifier with negative feedback over capacitor 136. In this condition any signals picked up on hydrophone 10 are amplified and fed to loud-speaker 120. The system also gives an indication of intruders in the pool vicinity. |
