two-tone generator

Both 555 oscillators or timers can be configured as audio oscillators, each for separate speakers. A dual 100kQ potentiometer is used to tune both oscillators simultaneously. The frequency range of the oscillator is controlled by a parallel transistor switch that selects the timing capacitor for the oscillator. Although this circuit only shows two ranges of switching circuits, many switching circuits can actually be added simply by replicating this parallel transistor switching circuit.