Digital oscillators often generate TTL- or CMOS-level outputs, referred to ground. Generating a symmetric bipolar output with respect to ground presents a challenge. In this design, four 1.5 V flashlight cells create ±3 V voltage sources, and the midpoint of cells acts as the ground reference (Figure 1). The oscillator at the input, based on the R1C1 time constant, generates a ±2.8 V bipolar output. The symmetrical output waveform requires no dc-blocking capability to drive a piezoelectric buzzer or loudspeaker. The circuit works well with ±1 to ±3 V sources and delivers a symmetrical output over the full range of source voltages.
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| Figure 1. | This oscillator uses multiple logic gates to deliver a symmetrical bipolar output. | |
