Moderators: Dave Moll, Andrew Davie, Steve Anderson
ac7zl wrote:...The problem arises when pulses are dropped (as per the NBTV standard) to denote start of frame. My synchronizer hunts around and never achieves lock.
1) Can you verify that it even works?
2) How well does it work? How stable is the picture and how quickly does it reach stability?
3) How do you effect frame lock?
4) Have you had any problems with it or have you noticed any irregularities?
Pete
AC7ZL
Viewmaster wrote:Interestingly, if you do a search for '4046' on this forum you will find many references to problems with sync using this pll. ...Certainly, the 4046 seems to cause more headaches for NBTV builders than most other items in the build. Albert.
Panrock wrote:Moreover I am using not one missing pulse but a bunch of four. This helps to ensure my heavy wheels synchronise not only in line lock, but automatically take up frame phase too. Steve O
Steve Anderson wrote:With the mechanical inertia of a disc/drum rotating at 750 RPM are line syncs required? Here I have to take the advice of the mechanical guys.
Viewmaster wrote:Interestingly, if you do a search for '4046' on this forum you will find many references to problems with sync using this pll. Some haven't achieved it and with others the picture bounces.
I sometimes wonder if more attention should be given to the sync holes in discs etc. Maybe they should be deburred more etc so that the output is constant?
As a unburred hole passes the opto fork (especially reflective steel/ali) there maybe unwanted reflections from the various shaped burrs which alter slightly the resultant output, thereby 'confusing' the 4046.....just a thought.
Certainly, the 4046 seems to cause more headaches for NBTV builders than most other items in the build.
Albert.
ac7zl wrote:I think signals from sync holes should be passed through buffers (schmidt trigger) with heavy hysteresis. It might also be of benefit to feed both the wheel feedback and reference sync signals through flip flops. This converts both into square wave streams with a 50% duty cycle. It seems to me that it should be easier, then, to make meaningful phase comparisons.
ac7zl wrote:You are correct in your cautions regarding simulators.... You can easily see an example of this by connecting a 1000 V voltage source to a little 1n4148 diode. The simulation shows 1700+ amps going through the diode! Yeah right! (The simulator does not show the flash of light, the puff of smoke, or the black stain left after the diode vanishes from this dimension.) Pete AC7ZL
Steve Anderson wrote:ac7zl wrote:You are correct in your cautions regarding simulators.... You can easily see an example of this by connecting a 1000 V voltage source to a little 1n4148 diode. The simulation shows 1700+ amps going through the diode! Yeah right! (The simulator does not show the flash of light, the puff of smoke, or the black stain left after the diode vanishes from this dimension.) Pete AC7ZL
I must try that! It could be quite a giggle! 1000V, 1700A, that's only 1.7 Mega Watts! Poor little 1N4148, what a way to go.
A real 'blaze of glory', even if it's for just a few microseconds!
Steve A.
Steve Anderson wrote:ac7zl wrote:I think signals from sync holes should be passed through buffers (schmidt trigger) with heavy hysteresis. It might also be of benefit to feed both the wheel feedback and reference sync signals through flip flops. This converts both into square wave streams with a 50% duty cycle. It seems to me that it should be easier, then, to make meaningful phase comparisons.
The idea of passing the signal through some form of 'clean-up' operation is wise. Below (Motor 1.gif) is the 'classic' implimetation of the motor control circuit as I understand it. It's my reference at the moment.
Motor 2.gif is a version that Klaas has developed that rightly adds some hysteresis to the opto-detector output.
PLL 2.gif is how I have done it using a LM311, but basically it's the same idea. It needs a a minimum of 600mV centred around 6V to get any output into the 4046. The edges are sharp (10ns or so) and don't bounce. The rest of the circuit to the right is unchanged.
On the subject of duty-cycle, as we're using Comparator II it doesn't care at all about the wave shape, it's activated only by the rising (positive going) input pulse edges. It couldn't care less about the following waveform until another positive-going edge comes along.
This is not true of PCI which does require a 50:50 duty-cycle input. But we're not using it, so no problem.
I also added a resistor in the emitter of the photo-transistor to stop over-dissipation should the 47k preset be turned to zero.
Steve A.
P.S. PLL 2.gif is very interim, hence Rxxx and so on....
ac7zl wrote:How do you guys effect frame sync with this circuit? It seems to me that the best this will do is line sync. Pete AC7ZL
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