A fairly bog standard 555 astable, the only quirk being that the timing capacitor goes to pin 3 through a single resistor rather than 7. The simulator shows a square wave output at about 500Hz. Calculating the expected output frequency (1/(2 ln 2 RC) ) yields an output frequency of just about 700 Hz, while actually building the thing (I measured the "47kΩ" resistor at 46.6kΩ, in fact) yields a nice square wave output at just about 1kHz. So what am I missing?
