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Tuesday, 18 June 2013

[www.keralites.net] Clock Tick-Tock Sound Generator & LED Pendulum

Clock Tick-Tock Sound Generator LED Pendulum

Wooden-case, battery-operated wall clocks with pendulums are available in the market. Some even have chimes. What is missing is the tick-tock sound of old mechanical pendulum clocks.

Fig. 1: Circuit of tick-tock sound generator

Fig. 2: Wooden clock

Fig. 1 shows the circuit of a tick-tock sound generator. It is built around timer IC 7555 (IC1) wired as an astable multivibrator. Resistor R1, preset VR1 and capacitor C1 generate frequencies that can be varied with the help of preset VR1. At output pin 3 of IC1, a small speaker is connected via capacitor C3 that produces the tick-tock sound. At pin 3 of IC1, two yellow LEDs are also connected on the clock face to flash in time with sound (see Fig. 2). Adjust preset VR1 such that ticking sound closely resembles the tick-tock of old pendulum clocks. Yellow LEDs (LED1 and LED2) match well with the wooden clock.

Fig. 3: Circuit for LED pendulum

Fig. 3 shows the circuit for the LED pendulum. It uses another timer 7555 wired in astable mode and its clock pulse at pin 3 is fed to clock pin 14 of decade counter 4017 (IC3). The outputs of IC3 are connected with the help of switching diode 1N4148 such that the six LEDs (LED3 through LED8) flash in sequence in one direction first and then in reverse sequence. The speed of flashing of LEDs can be adjusted with the help of 10-kilo-ohm preset VR2. Capacitor C6 (6.8nF) and resistor R11 (100-kilo-ohm) are used to reset the decade counter.

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Mount the LEDs either in 'V' shape or 'U' shape on the front panel of the cabinet (as shown in Fig. 4).

Fig. 4: Arrangement of LEDs on LED pendulum

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