I was going to say that Bertus (note spelling) has a good solution. I personally would use a real comparator instead of an op amp (and a poor one at that), but otherwise, it's a good solution.
We're interested in one signal that is frequency and duty cycle adjustable. If the frequency is such that full duty cycle adjustment > 100?, which is very possible, then the final output's frequency is affected.
We're interested in one signal that is frequency and duty cycle adjustable. If the frequency is such that full duty cycle adjustment > 100?, which is very possible, then the final output's frequency is affected.
You would probably want to set up the limit resistors on the ends of the duty cycle pot (10k) so that it goes from something like 1%-99%, or 10%-90%, or whatever, so that the frequency never goes to zero, which it will if the pot range is excessive on either end.
If, for example, you have a duty cycle pot set up to be 10-90% at f=1khz, then at f=2khz, full adjustment gives you 20% to 180%. Anything over 100% drives the output signal period to the one-shot, and screws up the output frequency.
You would probably want to set up the limit resistors on the ends of the duty cycle pot (10k) so that it goes from something like 1%-99%, or 10%-90%, or whatever, so that the frequency never goes to zero, which it will if the pot range is excessive on either end.
If, for example, you have a duty cycle pot set up to be 10-90% at f=1khz, then at f=2khz, full adjustment gives you 20% to 180%. Anything over 100% drives the output signal period to the one-shot, and screws up the output frequency.
It's not a oneshot, it's a comparator, slicing the triangle wave generated by the 555. If the comparator were ideal, the duty cycle would be absolutely independent of the frequency.
If, for example, you have a duty cycle pot set up to be 10-90% at f=1khz, then at f=2khz, full adjustment gives you 20% to 180%. Anything over 100% drives the output signal period to the one-shot, and screws up the output frequency.
Which is why (if you wanted to prevent 100% DC) you simply go to maximum frequency and dial in the R-C on the one shot to go to 95% duty cycle. Then, at lower frequencies, the maximum duty cycle is less than 95%.
The frequency would be wherever you set it, and the duty cycle would still be adjustable up to the maximum limit which would depend on the particular frequency.
Which is why (if you wanted to prevent 100% DC) you simply go to maximum frequency and dial in the R-C on the one shot to go to 95% duty cycle. Then, at lower frequencies, the maximum duty cycle is less than 95%.
The frequency would be wherever you set it, and the duty cycle would still be adjustable up to the maximum limit which would depend on the particular frequency.
A oneshot will not give constant duty cycle with varying frequency, unless you use a complicated feedback loop - which would have a response time issue.
It might better to use 82k for R5 and R6 and 100k for Pot1. Having both potentiometers the same value would be preferable because you don't have to stock more than one value for repairs.
A oneshot will not give constant duty cycle with varying frequency, unless you use a complicated feedback loop - which would have a response time issue.
Which is why (if you wanted to prevent 100% DC) you simply go to maximum frequency and dial in the R-C on the one shot to go to 95% duty cycle. Then, at lower frequencies, the maximum duty cycle is less than 95%.
The frequency would be wherever you set it, and the duty cycle would still be adjustable up to the maximum limit which would depend on the particular frequency.
I guess I missed that. What was the post number? And why did you carry on about oneshots, when that is clearly a separate circuit from a single timer IC?
I can't remember anyone saying that it has to use a 555 timer. The original poster's idea used a 555, but that doesn't mean it's mandatory.
If using a 555 is a requirement, to get round it, just add a comparator.
If no additional active parts other than a 555 are aloud then, as far as I'm aware, it's not possible to produce independently controllable frequency and duty cycle.
Unless this is a college assignment, I don't see the point, just use an LM393 and be done with it. The LM393 is cheaper than a 555 anyway.
PS: had anyone investigated using the using the bias pin for frequency and threshold for duty cycle? I've given it some thought, but I just can't imagine you can get much frequency range from the bias pin.
PS: had anyone investigated using the using the bias pin for frequency and threshold for duty cycle? I've given it some thought, but I just can't imagine you can get much frequency range from the bias pin.