DIY Scanning Disk TV - Videokarma.org TV - Video

mbates14 · #1 08-22-2005, 09:03 AM

Didnt know where to post this, so I thought here was good. I thought i would try something new, so I made a scanning disk TV, I burned a disk with some test audio for the disk, and I build the disk based off the design and schematic at this site:
http://bs.cyty.com/menschen/e-etzold...anningdisc.htm

I got everything working, but I have one problem. No Sync.

I have everything built according to the schematic.

But for some reason, my motor is running full tilt boogie. and its not slowing down to the incoming sync. I verified I have a sync pulse from the sync seperator, and I have somewhat of a pulse (even though its way higher in freq) from the optical fork on the disk. So thats working, Both signals are making it to the PLL circuitry, but for some reason, the gate is fully charged, driving it into saturation, which turns the motor on full way.

hmmm. Its no working. Can anyone give me any pointers? note: If i slow the disk down with a rheostat, I can see NBTV. so, I know my circuits are working, but If i hook the motor back up to the MOSFET, it runs full tilt boogie. If I unhook the gate, and ground it. the motor quits, so I know the FET is good.

my pulse from the optical fork, does NOT no where near look like the one on the site. My sync pulse from the seperator looks the same, but the disk fork doesnt. its more rounded and lots of noise, since I have to crank the oscop all the way down on the V/div to see it.

mbates14 · #2 08-22-2005, 10:11 AM

Figure this one out: If I disconnect pin16, which is the supply of the PLL chip, it starts working.

the motor speeds up when you first power it up, when you push play, it slows down to a constant speed.

mbates14 · #3 08-22-2005, 10:56 AM

nevermind. That dont work either, it just makes the motor vary with signal, but still dont sync, as I can block the fork, and it still isnt making any difference. Oh well.

old_tv_nut · #4 08-22-2005, 01:38 PM

You say your sync signal is very small? The 4046 is a high-voltage CMOS which requires its inputs to swing almost the full range from zero to supply voltage. If you are not getting a large sync pulse from your sync fork you need to fix that first. If you areusing the schematic at
http://bs.cyty.com/menschen/e-etzold...BTVmonitor.GIF
Note that the variable resistor in the phototransistor emitter should be 47k (47000) ohms. The "k" may be hard to read.

mbates14 · #5 08-22-2005, 02:16 PM

I have to crank up the drive to .05V/Div to see it good on the screen. but I have to mess with manual trigger, because of the noise.

I made the motor servo and the video/seperator circuit on two seperate power supply batteries, two seperate grounds. That doesnt make since either, how does the sync pulse return, if there is no return path between both stages (grounds are seperate). Both are 12V batteries.

I can see NBTV if I brake the disk. otherwise it spins too fast. motor is getting full 12v.

mbates14 · #6 08-22-2005, 02:18 PM

the biggest pot I have is a 10k. I even tried a 47K resistor, no noticable difference on the scope, its still weak, but its a little bit stronger.

100K resistor provides the strongest from the fork, but not enough I suppose.

mbates14 · #7 08-22-2005, 02:46 PM

I got a 100 K pot, and varied from top to bottom, I seen the signal peak to about 2v, so thats OK I guess.

But still, disk spins at full speed.

If I unhook the fork from the PLL chip, it slows down to whatever I set my speed pot at. as soon as I hook the phototransistor back in the circuit, it speeds up again.

What phase should the fork be, positive or negative? im thinking there is a phase problem or something I am totally stuck.

I got my phototransistor and LED from an old remote control and sensor, I took the sensor out of the IR module, and took the LED out of the remote.

mbates14 · #8 08-22-2005, 03:05 PM

im thinking there is a fault in the loop somewhere, but I read your site, and read the PLL section, and it did nothing but confuse the hell out of me

yagosaga · #9 08-22-2005, 04:41 PM

Quote:

Originally Posted by mbates14

I thought i would try something new, so I made a scanning disk TV ... I got everything working, but I have one problem. No Sync. ... But for some reason, my motor is running full tilt boogie. and its not slowing down to the incoming sync.

That's exactly the same result which I got when I have built the motor drive circuit according to Peter Smith's schematics:
http://www.nbtv.wyenet.co.uk/speedctrlckt.gif
First check the pulse from the opto fork. I had to vary the distance of the light emitting diode to find the point were I get the best pulse. When I have found it, the adjustment of the 47K poti was not critical.
If you compare Peter Smith's schematics with mine you will see that I had done some changes. These were necessary for getting a line sync. The frame sync is not working well now. The 4046 needs a clear-cut digital input signal. In the next step I will insert a Schmitt-trigger between the opto fork and the 4046.
Another problem is the IRF520. The original IRF510 (which I couldn't get here) needs a lower gain for regulating the motor speed. The IRF520 will be overdrived by the 4046, so I lowered the input voltage.

mbates14 · #10 08-22-2005, 05:48 PM

I tried the IRF510, I also tried a 2sk somethinanother. And it didnt work.

I notice on your scope pic, you got a clean signal from the fork. Mine is all noisey and very jumpy.

Any ideas?

(My disc is made out of cardboard, Very thin cardboard based off your excel sheets, and it scans fine. Clean picture, formatted to fit a standard sheet of paper).

mbates14 · #11 08-22-2005, 05:50 PM

I built mine based of your schematics.

I only have a TL072 and a LM741 op amps. Not the CAblah blah blah.

So I used those. The video works fine. But the motor servo is not workin period. If I disconnect the reference signal, it slows down to whatever I have the pot set at. As soon as I connect the reference signal, zrrrrroooommm. full speed.

My disc isnt 12 inches, its more like 6 to 8 inches (ran off a computer).

But If I get the disc to speed and scan normally by manual braking, the pulses on the scope look exact same compared to the reference signal, so I know thats not the issue. The servo isnt doing the job. The comparator isnt working, its like its adding the phases, not subtracting them.

Both the reference and fork pulses are positive. Isnt one of them supposed to be inverted? or not.

Isnt it supposed to find the difference between the two phases, and generate an offset voltage? or not. I dont know how PLL works, so bare with me. If it has to find the difference, then one of the signals MUST be inverted, or oscillation will occur? both signals are positive.

mbates14 · #12 08-22-2005, 06:03 PM

also forgot to mention, ive got everything breadboarded. I can move around, add, subtract, or whatever as necessary.

The whole entire thing is made out of cardboard. (its amazing what you can do with an old detergent box).

the disk had thick cardboard, That proved to be off center, and couldnt see the light, and wobbled.

So I used a very thin cardboard, and precisely punched the holes, including the center one. I left the pattern on the disc, and put it on the motor shaft and hotglued it. it spins up, and the circle around the hole is dead center, It doesnt bobb as if it were off-center. Its perfectly still, even though the disk is turning. So I know my disk is good.

mbates14 · #13 08-22-2005, 06:51 PM

I give up. Ive tried everything. I just shortened the fork as close as I can get it without scraping the disk, and still full speed.

CRRRAAAPPPP. Nothing works. Stupid ass TV.

bele2009 · #14 08-22-2005, 07:45 PM

mbates14,

Your PLL circuit or your opto-sensor are not working. Remove your scanning disc so the light beam reach the detector side without problem. Then measure the DC voltage reading at pin 3 of the 4046. In this condition the photo-transistor in the opto-sensor should be in full conduction and you should have close to 12V on pin 3. While you are at it, also take a voltage reading on both sides of the LED side of the opto-sensor.

Place a piece of cardbord in the slot to hide the ligh then recheck the voltage at pin 3. You should now have close to 0 volt DC.

Then I'll try to see what's wrong with your circuit.

Come to think about it, you said that you are powering your circuit from two separate batteries. It does not show on the schematic, but I think the two GNDs (-)should be connected together or your sync pulse won't have any effect on the PLL circuit !

Good luck !

Eric

mbates14 · #15 08-22-2005, 08:43 PM

Hey, What I did was built a PNP amplifier off the photodetector. I can see a good strong signal now.

And It still didnt solve my problem, but for kicks, I took the reference and fork signals and switched them on the PLL. Now, its trying to lock!!!

Itll lock, and as soon as it locks, it will quickly drop off, and lock again. and again and again. I can hear the motor slowing and speeding. So, the PLL is working.

I took the signals on pin 3 and pin 14 and switched them. Now its trying to work.