Who has used the 4046 to synchronize their nipkow wheels?
Posted: Wed Apr 23, 2008 9:46 am
If you've read some of my other posts, you have no doubt gathered that I am tinkering with NBTV circuitry in the virtual (SPICE) world. I have modeled and developed various circuits for video, gamma, dc restoration and sync extraction. The one thing that has me stumped is synchronization.
I have worked out interesting circuits using D flipflops and XOR gates to detect phase differences, and I've modeled the Nipkow disk and its sync holes with a voltage controlled pulse generator. Standard spice voltage sources are used to generate sync reference pulse trains.
If the ref and wheel pulse trains are devoid of the (missing) frame pulse, the circuitry seems to work fine. In fact, I can go from wheel at dead stop, spin it up, and synchronize perfectly with the reference pulses, and in fairly short order.
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.
Thinking that there might be something inherently wrong with my phase detector, I employed a SPICE model of the 4046. Again, where pulse trains are continuous (i.e., no missing frame pulse) the closed-loop control works like a charm. If I use signal sources that feature missing frame pulses, it doesn't work right.
I wonder if anyone could give me feedback with regard to "standard" NBTV 4046 circuit that is in circulation.
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?
Many puzzled thanks,
Pete
AC7ZL
I have worked out interesting circuits using D flipflops and XOR gates to detect phase differences, and I've modeled the Nipkow disk and its sync holes with a voltage controlled pulse generator. Standard spice voltage sources are used to generate sync reference pulse trains.
If the ref and wheel pulse trains are devoid of the (missing) frame pulse, the circuitry seems to work fine. In fact, I can go from wheel at dead stop, spin it up, and synchronize perfectly with the reference pulses, and in fairly short order.
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.
Thinking that there might be something inherently wrong with my phase detector, I employed a SPICE model of the 4046. Again, where pulse trains are continuous (i.e., no missing frame pulse) the closed-loop control works like a charm. If I use signal sources that feature missing frame pulses, it doesn't work right.
I wonder if anyone could give me feedback with regard to "standard" NBTV 4046 circuit that is in circulation.
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?
Many puzzled thanks,
Pete
AC7ZL