Frank says Rob is right. See Fig. 1, the dimmer schematic. The 555 Timer IC does produce a fairly square wave output, so filtering is important. However, the 6.8K resistor that is in a series with the ...

Connecting the existing power supply to his oscilloscope, [Matthew] found the stock “steady on” setting was a 72 VAC peak-to-peak square wave at about ... waves with a 555 timer and a 74HC74D ...

The electronic circuit is basically a square wave generator using the common LM555 timer IC. It is followed by a final stage made of transistors T1 and T2. The actual doubler circuit is made of D1, D2 ...

The cheapest and most common inverters have modified square wave outputs, which yield a waveform that’s good enough for most electronics and avoids the extra expense of producing a pure ...