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555 timer pulse width circuit

 
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JingleJoe
HG Supreme


Joined: 01 Apr 2009
Posts: 52
Location: England

PostPosted: Wed Jun 01, 2011 4:43 am    Post subject: 555 timer pulse width circuit Reply with quote

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. Smile
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andrewblog
Semi Newbie


Joined: 01 Jun 2011
Posts: 7

PostPosted: Thu Jun 02, 2011 5:45 am    Post subject: Reply with quote

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/
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JingleJoe
HG Supreme


Joined: 01 Apr 2009
Posts: 52
Location: England

PostPosted: Thu Jun 02, 2011 4:33 pm    Post subject: Reply with quote

andrewblog wrote:
I don't know what exactly you are doing

Making a circuit in which the pulse width can be changed without altering the frequency.

Thanks for the effort with your diagram and that link though, the calculator will definately be useful Smile
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