Originally posted by bussi04
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First please give me a link to the exact 4046 IC you use, if it is a Philips, it must be a Philips data sheet. No more misunderstandings.
Assuming the IC adheres to my data sheet, I continue, as this must be designed to work, we don't get lucky by trial and error.
1. According to my data sheet the max VCO frequency is approx. around 300kHz, so the first design decision is to chose a center frequency of 160kHz. Set SW1 to 10 kohm. C12 = 100pF.
2. Like an internal combustion engine has a gearbox to make it happy in its best RPM range, we have U12..U14 to let the VCO run at 160kHz and divide down to what we need.
And now we get to a real error: The choice of 4017 is a bad choice as it is a decade counter so we have division factors 1, 10, 100, 1000.
None of these are good for the final use, maybe except a factor of 1.
So instead of 3 pcs 4017 I would like to have only one 4024 ripple counter offering factors 1, 2, 4, 8, 16, 32, 64, 128.
For the final use I would use the factor 4, and for the test I would use 32.
pin13 of U4 needs a pullup resistor because itīs tristate
What you see is a control loop saturated a one rail. The working voltage on C10 should be approx. 2.5V +- 1V, when everything is OK.
R12, R13 and C10 acts as an integrator of the square wave output from the phase comparator, except when the frequency is bulls eye, then it is 3-stated to keep the C10 voltage constant. The integrator sets the delta freq / delta time, or the rate of change of frequency per time unit. Too slow, and you never lock in, too fast and it will be unstable.
So get a 4024 IC and put it on the breadboard. Use the Q2 output (pin11) to U4 pin 3.
Alternatively have the VCO center frequency at 40kHz and divide by 10 (SW7 C-position), SW1 A-position C12 100pF.
Be sure to try reversing the wires to P3 and P4 so you can see the difference between positive and negative feedback.
And of cause U3 must start scanning below 4kHz. Except for the switchover switch (U6) I'm quite confident this should work OK.
Good luck
Eric
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