Timed Beeper

Beeps 7.5 seconds after a preset time

Adjustable time settings: 15 s. 30 s. 1 min. 2 min. & others

Circuit diagram:

MiniTimer circuit diagram


R1______220R   1/4W Resistor
R2_______10M   1/4W Resistor
R3________1M   1/4W Resistor
R4_______10K   1/4W Resistor
R5_______47K   1/4W Resistor

C1_______100nF  63V Polyester Capacitor
C2________22µF  25V Electrolytic Capacitor

D1______1N4148  75V 150mA Diode
D2________3mm.  Red LED

IC1_____4081   Quad 2 input AND Gate IC
IC2_____4060   14 stage ripple counter and oscillator IC

Q1______BC337  45V 800mA NPN Transistor

P1______SPST Pushbutton (Start)
P2______SPST Pushbutton (Reset)

SW1_____4 ways Switch (See notes)

PS______Piezo sounder (incorporating 3KHz oscillator)

B1______3V Battery (2 AA 1.5V Cells in series)

Device purpose:

This circuit is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it is a modern substitute for the old sandglass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.

Circuit operation:

Pushing on P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is around 4Hz. LED D2, driven by IC1A & B, flashing at the same oscillator frequency, will signal proper circuit operation. SW1 selects the appropriate pin of IC2 to adjust timing duration:

When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push on P2.