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Timed Beeper (CD4081)

2016-10-12 22:27  
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This article describes the Timed Beeper (CD4081). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: CD4081.

 

Beeps 7.5 seconds after a preset time

Circuit diagram:

MiniTimer circuit diagram

Parts:

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)

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.

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.

 


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