DIY Scanning Disk TV

[mbates14]

One thing I do notice, if i bring the fork closer together, the disk speeds all the way up. if i bring it back, it works fine. (opposite as it should, but like i said before, i got the inputs switched).

if i switch them back to normal, it wont work at all.

[old_tv_nut]

The only way I know to solve a loop problem is to break the loop and measure each part.

So, I think the first thing is to measure the fork pulse going into the chip (with a scope) and see what the heck it's doing when you move it. IF it is good, moving it closer shouldn't hurt, should just make the pulse sharper (steeper sides), as it clips at zero and 12 volts.

Another part is the motor control - disconnect it from the chip output and ground that lead, and the motor should stop or slow way down; connect it to 12 volts and the motor should race. If you can connect that lead to the wiper of a pot (say 10 k), with the ends of the pot at ground and +12, you should be able to manually control the speed - and the right speed should be with the wiper approximately centered. If not, your motor control circuit is not centered and it may be impossible for the circuit to reliably control it. If it's running too fast, you need to either put in a pulley system or perhaps put a high power resistor in series with the motor. I can't tell you what the value and wattage should be without knowing how much current your motor draws.

The third thing to check is the chip operation. You can look at the output with a scope or a voltmeter. Onc eyuou know the fork pulses and sync pusles are OK, reconnect the whole circuit. When the disc is too slow (like the fork is blocked), you should see a high-duty cycle waveform on the chip output that has a DC average (voltmeter reading) close to 12 volts. When the disc is running away at high speed, you should see a low-duty cycle waveform that has a DC average close to zero volts.

When everything is centered on its nominal range and the whole circuit is connected and working, the chip output should average about 1/2 of the power suypply, or 6 volts.

I'm suspicious that your motor is just too uncontrollably fast and needs to be slowed down - If you are running the speed setting close to the "slow" end to achieve this, you may need some other fix to make the adjustment more centered. But you need to check the operation of all the parts, especially first why are you getting such strange results when you move the fork.

[yagosaga]

Originally Posted by mbates14

but its working now.

Congratulations!

Originally Posted by mbates14

More or less, i have line lock, but not so much frame lock. I covered one of the holes btw.

With some "fine tuning" you can improve the line lock. I don't have a save frame lock too. This depends on bad input signals, I still have to do some work here. For frame sync I have installed a switch which interupts the sync pulse for the 4046. When pressing the button of the switch, the motor slows down and afterwards it is locked. In half of starting the disk the motor will be in correct frame sync (plus minus one line). In the other half I push the button.
What I still have is some kind of jitter. The picture in sync is moving slowly up and down. This depends on the reference pulse from the opto fork. The pulse is more a sine wave than a square-wave type.

[mbates14]

mine are just little noisy peaks comming from the fork. They get bigger when I draw it closer together, but it never goes into clipping. It rubs the disk first.

[mbates14]

I know the LED is drawing some current, because the 680 ohm resistor gets hotter than a fire cracker.

[mbates14]

ok. I took some measurements.

I flipped the sync inputs back to normal.


I put my multimeter on DC, and started up the CD player, and pushed pause. and powered the circuit up. The output on the IC was around 5.6v

as soon as I pushed play, it jumped to about 12.6V i pushed pause, it dropped to 11.9, but no noticable speed change on the motor. I push play again, it goes up to 12.6 I have a b+ of about 13.5vdc

if i put the syncs backwards again, it stays at 0 volts. and then itll occasionally spike to 2.4 to try to lock the picture, but quickly falls to 0v, most likely because im using the disk as the reference, and sync as the loop signal (backwards, only way it attempts to work).


If only I had a function generator, i could pump a "fake" signal in place of where the optical fork is, and see if its the circuit or the fork.

[mbates14]

nevermind, EDIT: I didnt have my probe grounded properly.

Anyway, even though I remove sync, or anything, the voltage still holds at 12.6vdc.

[mbates14]

its definatly the optical fork.


now that i put a ton of capacitors to bypass the power supplys really well, the noise is gone. i get good peaks from the fork, but its not working.

If i unhook the fork from the chip, as soon as I power down the CD player, or pause it, the disk stops. when i power it on, it goes.

if i hook the fork up, it stays on, never stops.

my meter reads .9vac from the fork output, and 1vac from the sync seperator output. Can I run a fork in like an LM386 audio amplifier? or not.

[mbates14]

I figured out the problem I think.

Ok, i got the syncs back where they are supposed to be. I built an LM386 amp, and tied it to the fork. now, the output is going into clipping, but no more speed off. now it stops as you stop the disk, and speeds up to near normal when you play this disk, itll try to lock, but it wont lock the phase. itll slow down, or speed up, but never maintain.

im assuming because its clipped now, and i have to amp up the reference sync pulse. I guess??

[mbates14]

its working now, if I cover the fork, its speeds off.

if i uncover it, it slows down, but wont lock the frame, now there isnt any stable line lock. ill be lucky if it locks for 2 microseconds.

[mbates14]

I give up. im doing away with the PLL crap. Im just going to use the course and fine controls to operate a lm317 regulator to drive the motor. that way it wont jump around and loose lock every 2 nanoseconds.

[yagosaga]

Is it possible to post some photos of your machine? And the recent schematics too? In the moment it is too complicated to reconstruct what you had done.

[old_tv_nut]

It sounds like you are getting closer - if you post the schematics, maybe we can work through it. To repeat, when a closed-loop system doesn't work right, it's really hard to tell what the problem is without opening the loop and measuring the pieces individually. Willing to help step through it if you have the patience.

[mbates14]

I have a question, maybe the more knowlegeable guys could answer.

I gotten ahold of a stepper motor, wiring schematics and diagram, and got a motor controller IC.

Steppers i heard are very accurate. You would think using a stepper motor for this project would make frame lock VERY easy, and very rock solid.

Any ideas on how to make one sync up? I no nothing about stepper motors.

[mbates14]

The only thing I coudl think of, is building the servo circuit, and using a hex inverter, with an AND gate to clean up the sync pulse to make it digital-like, and then using that now converted clock of 12.5hz to drive the step input of the controller, but that only works if it was one revolution per step, which is never the case. I would have to calibrate it somehow. If i used the sync seperater output to drive the servo directly, then no need for optical block, or pll. Because steppers are that damn accurate. lol.