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This allows the frequency to be reduced, but reduces the adjustable duty cycle range also (Just a note to ikelectro)Put another pot, connected as a rheostat, in series with the wiper output of R2.
Try inserting a 500K pot (or, perhaps, even greater value) between pin 1 and the wire connected to pin 1. That should influence the trip points of the circuit, and thus the frequency, leaving the duty cycle adjustment, and range of adjustment, largely unaffected. The pot should influence the trips points due to voltage drop across it resulting from the small amount of input bias current of the IC.
An alternative route is get rid of the series pot at pin 1 altogether, put a 10K pot in series with each of the two diodes, and replace the existing 10K pot with a short circuit. The duty cycle adjustment will not be independent of the frequency adjustment, but the ON time of the pulses is adjusted with one of the pots, while the OFF time is adjusted with the other pot. So, at least, the ON time and the OFF time are independently settable, allowing you to adjust the frequency and duty cycle.
I'm not getting it. I mean Im not understanding it... can you please draw me the circuit what have you written..
Like this:
ok; I'll do it.....
can you suggest me what IC (rather than 74HC14) should i use as frequency generator where i can also change the duty cycle. and that should be within the range of 3V (VCC of the IC)???
With the changes you have made, what requirements remain unsatisfied, if any?
There is only one, but not big one!!!
with the both 10 KΩ I have to fix the duty and frequency.. but the problem is that these two factors( duty cycle and frequency) are changing with the other one. I mean at the time adjusting the duty cycle the frequency is changing a lot and vice versa!!!!!
at a moment I am not able to change the frequency because the 10 K pot went it extreme and the giving frequency is about 35 KHz or something like that in a particular duty cycle.....
You can get independent frequency and mark-space control with a four-gate circuit. Mark-space ratio is adjustable ~ 8% to 92%. If I can attach the schematic successfully it's here:
View attachment 69848
Edit: I used a CD40106 because of its symmetrical Schmitt threshold values. You could use a 74HC14 instead, but you might have to tinker with R1 and R6 values to allow for threshold asymmetry.
You can connect the pots as shown in this attached. The Freq and PW are independently settable. The issue with this configuation is that the duty cycle is adjustable from only 0 to 50% when the Freq is adjusted to the lowest value (0 to 100% when the Freq is adjusted to the highest value). The thing to do then is to add an inverter, as shown, and use the OUT2 to get the 50-100% side of the duty cycle.
I have just doing your circuit in my bread board and I'm getting this..
I set the fre 45KHz at 80 % duty. then I try to get 50% duty cycle at the same frequency(45KHz). if Im adjusting the 10KΩ pot for 50 duty cycle automatically the frequency comes to 50Khz......
and the frequency is not getting smaller than 28 or 27 Khz at all the duty cycle I have tried...