Posted on Dec 19, 2012

A variable dock-pulse generator is made up of two sections of IC1 (a 4069 CMOS hex inverter). Rl, Sl, and capacitors Cl through C6. By adjusting Rl and switching one of the capacitors into the circuit, the clock`s pulse rate can be varied over a wide range. The TL507C converts analog signals-in this case the output of IC3, an LM386 audio amplifier -into digital signals.

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The conversion is accomplished using the single-slope method; it involves comparing an internally generated ramp signal to the analog input signal and a 200-mV reference voltage. The square-wave output from the aid converter is fed to IC3 through a network consisting of R2, R3, and C7. Resistor R2 controls the amplitude of the pulses. Resistor R3 and capacitor C7 form a variable tone-control filter and a differentiator circuit that converts a square wave into a spiked waveform. That waveform is amplified by IC3, and the resulting output is fed back into the analog input of IC2, as well as to an 8-0 speaker. By adjusting Rl and selecting one of the six capacitors with Sl-thus varying the clock frequency-and by varying R2 and R3, you can produce many sounds.

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