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One second Audible Clock Circuit Schematic

Accurate, finger-operated portable unit, 3 - 12V Battery supply

This accurate one-pulse-per-second clock is made with a few common parts and driven from a 50 or 60 Hertz mains supply but with no direct connection to it. A beep or metronome-like click and/or a visible flash, will beat the one-second time and can be useful in many applications in which some sort of time-delay counting in seconds is desirable. The circuit is formed by a CMos 4024 counter/divider chip and 3 diodes, arranged to divide the frequency of the input signal at pin #1 by 50 (or 60, see Notes).

The input impedance at pin #1 is very hight, so simply touching the pin (or a short track or piece of wire connected to it) is usually enough to provide the necessary input signal. Another way to provide an input signal consists in a piece of wire wrapped several times around any convenient mains cable or transformer. No other connection is necessary.

Circuit diagram:
 One second audible clock schematic circuit diagram
One second Audible Clock Circuit Diagram


R1 = 10K
R2 = 47.K
R3 = 100R
C1 = 1nF-63V
C2 = 10µF-25V
C3 = 100nF-63V
D1 = 1N4148
D2 = 1N4148
D3 = 1N4148
D4 = LED-(Optional, any shape and color, see Notes)
D5 = 1N4148-75V 150mA Diode (Optional, see Notes)
Q1 = BC337-45V 800mA NPN Transistor
IC1 = 4024-7 stage ripple counter IC
BZ1 = Piezo sounder (incorporating 3KHz oscillator)
SPKR = 8 Ohm, 40 - 50mm diameter Loudspeaker (Optional, see Notes)
SW1 = SPST Toggle or Slide Switch (Optional, see Notes)
B1 = 3 to 12V Battery (See Notes)