This simple alarm timer circuit is made with 4060 which has an integrated oscillator with a good stability with a relatively wide frequency range. In the circuit diagram the oscillator frequency is set by the RC network that is connected at pins 9, 10 and 11.
When the timer with alarm circuit is connected with S1, the pulse from R4 and C2 common point will reset the counter and will start the counting. When it reaches 14 bit, the 13 pin passes in state H and the auto oscillating buzzer is powered by the control transistor T1.
The time interval is adjusted with P1. In order to get intervals ranging from one minute to two hours we should do a proper sizing of the oscillator components:
- 1 to 30 minutes: C1=220nF; P1=500KΩ
- 1 to 60 minutes: C1=470nf; P1=500KΩ
- 1 to 120 minutes: C1=470nF; P1=1MΩ
The power supply of the timer alarm is from a 9V battery. D1 led does not does not affect the operation of the circuit and was included only to show that it works. So, R3 and D1 are optional components.
S1 can be a tilt-sensitive switch with mercury if that will be used as a kitchen clock. With the buzzer on the power consumption of the timer alarm will be around 10 mA.
Timer Alarm circuit diagram
P1 = 500kΩ (* read the list above)
R1 = 2.2MΩ
R2 = 18kΩ
R3 = R5 = 1kΩ
R4 = 1MΩ
C1 = 220nF (* read the list above)
C2 = 10nF
T1 = BC547
IC1 = 4060