Audio operated relay

  
Ql and Q2 are general purpose transistors. The 10 K input pot is adjusted to a point just short of where Ql turns on as indicated by K pulling in. K is any 5 V reed relay. With the values shown for R (100 K) and C (47 µf), timing values from 5 to slightly over 5 seconds can be achieved
Audio operated relay - schematic

B shows the addition of a 22 ? series resistor to the 10K input pot if a 12 V supply is used. A suitable 12 V reed relay must be used at K.




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