On Wed, Dec 18, 2013, at 11:49 PM, Lindy Mayfield wrote:
> This got me into confusion before, and it's still not clear, what duty
> cycle is.  Meaning that I don't understand your answer. Yet.  :-)
>=20
> The frequency is the time between pulses.  The duty cycle is the
> percentage of time the line is high.  So I guess that a perfect square
> wave would have a duty cycle of 50%?

Yes. And the basic 555 astable circuit is limited 50% to 100% duty
cycle. Servos require a 1ms to 2ms pulse about 50 times per second,
which looks like a very low duty cycle. Hence the transistor to invert
the output.

Note that servos set their position based on the positive pulse. The low
period should have no effect on the position, it just needs to be above
a certain minimum or the servo goes nuts.

> And also, I am going to try to put together your schematic on a
> breadboard.  (That's usually as far as I get with "projects" at the
> moment.)   I think I have all the parts, except for U2, I have to look up
> what that is.

U2 is just a 5 volt regulator, the drawing I sent was originally for a
12 volt application. If you have 5 to 6 volts available you can skip the
regulator section.

Best regards, Bob

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