555 timer pulse width circuit

[JingleJoe]

God damn I love 555 timers.
I've been playing with them for days now, I've got my astable circuits figured out however I had problems maintaining a steady frequency in a circuit made for pulse width modulation. I think that's the right name for it, whatever, it's a circuit that changes the pulse width.

Initially I was changing the value of R1, but this alters the frequency aswell as pulse width, however I have a possible solution;





Here is an astable circuit to see where my alterations fit in;


sauce: http://www.kpsec.freeuk.com/555timer.htm



I haven't tried it yet so do you think my circuit would work? Maintain one frequency but modulate pulse width? Any alterations?


I'll make it later and post what happens but I want to know what some other electronics nerds think.
_________________
The Green Dungeon Alchemist.

[andrewblog]

I don't know what exactly you are doing, but if you want the low period longer than the high period you can invert the signal from the output of the 555.
http://imageshack.us/photo/my-images/191/bozza1m.jpg/
Here the output drives the pin 15 of a 4017IC. If you connect the central pin of a second transistor (instead of the pin 15) it should work.
Take a look at this calculator:
http://freespace.virgin.net/matt.waite/resource/handy/pinouts/555/

[JingleJoe]