SELECTIVE TIMER ALARM

1.  A timer circuit using IC 4060 is given here. The IC 4060 is a 14 stage binary counter with a built-in oscillator.
2. R2, R7, C1 are the components that determine the frequency of the oscillator and the outputs will become high one after other and only one at a time.
3.  The last five outputs are only used here. The high pulses from the outputs are used to trigger the NE555 IC.
4.  Here NE555 is wired as a monostable multivibrator. The buzzer will produce the alarm when the output of IC2 goes high.
5.  The duration of the alarm depends on the components C3 and R5.The duration can be adjusted by varying the value of C3.
6.  The alarm will automatically turn OFF after the predetermined time. The trigger pin of IC2 will be normally positive.
7.  When the Q1 is forward biased by the positive pulse at its base from IC1, the capacitor C2 becomes charged and reduces the voltage at trigger pin of IC2.This triggers the IC.When the capacitor is fully charged the pin 2 becomes again positive.
8.  The maximum duration from timer IC 4060 will be at pin 3. The times decrease by half in the pins 2, 3, 15, and 13 respectively. The timer duration can be varied by varying the capacitor C1.

       NOTES:

• Use 6V DC for powering the circuit.
• Assemble the circuit on a good quality PCB.
• Mount the ICs on holders.
• The switch S2 can be a single pole five throw rotary switch.
• The switch S1 can be a push button switch.
• S1 is used to reset the timer.
• S2 is used to select the alarm time.
• R7 can be used for the fine adjustment of alarm time.