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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
EastVoltResearc wrote ...
Just use two 555 timers. One controls PRF, and the other pulsewidth, so you can control frequency and duty cycle independently.
I know that I can use two 555s. The question then becomes "if I can vary the PRF on the first 555 with a pot, how do I ensure the pulse width on the second 555 does not exceed the period of the first 555 and still allow close to 0-100% duty variation?"
I think the link I posted earlier will solve the problem.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I couldn't view the PDF for some reason, it said it was corrupt
I still think you need to move away from 555s for what you're doing, instead of trying to patch the problems that are caused by using 2 like that. 555s are only good up to a point, but there are better ways to achieve independent variation of frequency/duty cycle probably using less components than are contained within a single 555. this page explains it pretty well, look at 2.1.1. the comparator. You vary the frequency of the 'triangle wave generator' for your frequency, and the voltage of the 'DC Level' for your duty cycle.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I just rigged up a crude setup that works just fine. I used the 555 to set up the frequency and a 741 opamp to control the pulse width. If I ever need this for a project I will just fine tune the components.
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Function Generator question
