I hooked up a small circuit I found towards the bottom of this url and plotted the result in a spreadsheet (figure 1). Figure 2 shows the DC-coupled output waveform at 12V input. Only the frequency changes at different input voltages. So what's going on here? Figure 1: Figure 2: Hint 1: Relaxation oscillator Hint 2: 2N2222 datasheet Hint 3: PN junction EDIT - To avoid confusion: The Vce voltage from the table in Figure 1 is the 'DC' voltage measured with a multimeter.