#785 Tick Tock

A 555/74LS73 circuit that generates a tick-tock sound sequence at distinct frequencies.

Here’s a quick demo..

Notes

I wanted to create a mechanical clock-like “tick-tock” sound generator. I’ve found some inspiration in existing circuits:

• Tic-Tic Sound Generator using IC 555
• Tick Tock Sound Generator Circuit using 555 Timer IC
• Clock with LED Pendulum and Tick Tock Sound

However they all seem to cheat and generate the tick/tock pulses at the same frequency. Some circuits don’t actually set a frequency, and just rely on a single click of the speaker. I want something better, where the audio frequencies are specific and distinct for tick and tock.

The circuit I’ve come up with here is quite a naïve composition of the elements needed to build up a tunable tick-tock sound:

• adjustable clock frequency (precalculated for 1 Hz)
• specific “tick” and “tock” frequencies
  • can be altered by changing R5,R6,C4 values
  • could be made user-adjustable by replacing R5 and R6 with pots

There is probably a much more elegant and straight-forward way to achieve this, but I haven’t a suitable circuit yet. Something to ponder..

Circuit Design

Designed with Fritzing: see TickTock.fzz.

• U1: 555 configured as a low-frequency oscillator to provide the time signal:
  • 1Hz @ 50.7% duty cycle
  • with R1 = 2kΩ, R2 = 71kΩ (100kΩ pot), C1 = 10µF
• U2: 555 monostable edge-triggered by U1, converts the time sync to short pulses of defined duration (TICK):
  • 52ms high
  • with R3 = 4.7kΩ, C3 = 10µF
• U3: 555 audio oscillator
  • enabled by U2 high pulses (TICK) to the control pin.
  • base frequency:
    • 1252 Hz
    • with R5 = 1kΩ, R6+R7 = 57kΩ, C4 = 10nF
  • high frequency, when FNOTCH high causing R7 bypass:
    • 1516 Hz
    • with R5 = 1kΩ, R6 = 47kΩ, C4 = 10nF
• U4: 74LS73 latch
  • clocked by U2 pulses (TICK)
  • alternating high/low Q1 output (FNOTCH)

For the breadboard build, I have added LED+Resistor indicators to the main signals: CLOCK, TICK FNOTCH (Q1 and ~Q1), AF. These are not shown in the schematic.

The distinct tick/tock signals are capture on the scope below, where:

• CH1 (Yellow) - AF output from U3
• CH2 (Blue) - TICK output from U2
• CH3 (Red) - CLOCK output from U1

Credits and References

• LM555 Datasheet
• 74LS73 datasheet - Dual JK Flip-Flop with Clear
• Visual 555 Calculator