Output 'on' (high) to 'off' (low) ratio. 50% duty cycle would be equal high and low time per cycle. 90% duty cycle would be output high most of the cycle.
Here is a sinewave output from a 555: **broken link removed**
The output has "high impedance" and needs buffering. In other words, the output waveform is "very delicate" and will change shape if it is loaded or passed to a stage that has a low resistance.
You will have to choose values for R and C (on the output) to get the waveshape you require. It is not a perfect sinewave but is called "an approximation."
Depends on if you actually need a real sinewave or not antknee, colins circuit will give you a filtered square wave output, I'd hardly consider it a sinewave, it'll jut be a bit more gentle than a square wave, it'll still contain plenty of harmonics.
I don't need an exact sine wave. I will have a look to see if the harmonics are going to be an issue. Cheers. Am going to put it together now at 100KHz.
One way to get a nice sine wave out of a 555 is to filter the (square wave) output with an LC filter rather than an RC filter. If the frequency is not too low a small inductor will do the job. The LC filter should follow the resonate frequency formula for L and C:
F=1/(2*pi*sqrt(L*C))
In other words, if the output is 10kHz then L and C must be such that in the above formula F=10kHz also.
Of course this is best when you only need one sine wave frequency output, as C will have to change for somewhat different frequencies.
That is excellent thank you. I just tried it with two 10uF caps and 3.3K resistor because those are closest to hand. The square wave has rounded off a little, it is hard to tell if I'm getting minus volts, I presume so, but I have difficulty working out how to ground my scope so it is hard to tell!