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How to build Amplifier Timer Circuit Schematic

2015-01-02 22:17  
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This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting.

Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.

Circuit diagram:

Circuit diagram


R1,R8___________1K 1/4W ResistorsR2,R3___________4K7 1/4W ResistorsR4_____________22K 1/4W ResistorR5______________4M7 1/4W ResistorR6,R9__________10K 1/4W ResistorsR7______________1M5 1/4W ResistorR10___________100K 1/4W ResistorR11____________15K 1/4W ResistorR12____________10M 1/4W ResistorR13_____________1M 1/4W ResistorR14_____________8K2 1/4W ResistorR15_____________1K8 1/4W ResistorC1____________470μF 25V Electrolytic CapacitorC2,C3,C6______100nF 63V Polyester CapacitorsC4,C5__________10μF 25V Electrolytic CapacitorsD1_____Diode bridge 100V 1AD2,D7________1N4002 100V 1A DiodesD3__________Red LED 5mm.D4_______Yellow LED 5mm.D5,D6________1N4148 75V 150mA DiodesIC1___________78L12 12V 100mA Voltage regulator ICIC2___________LM358 Low Power Dual Op-ampIC3____________4060 14 stage ripple counter and oscillator ICQ1____________BC557 45V 100mA PNP TransistorQ2____________BC337 45V 800mA NPN TransistorJ1______________RCA audio input socketP1_____________SPST Mains suited PushbuttonP2_____________SPST PushbuttonT1_____________220V Primary, 12V Secondary 3VA Mains transformerRL1___________10.5V 270 Ohm Relay with SPST 5A 220V switchPL1____________Male Mains plugSK1__________Female Mains socket


Simply connect left or right channel tape output of your amplifier to J1.You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.The delay time can be varied changing R13 and/or C6 values.Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.

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