32 line manila disc televisor project (sync issues)

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32 line manila disc televisor project (sync issues)

Postby aussie_bloke » Wed Nov 16, 2022 9:48 pm

G'day all.

Back in 2017 I built a 32 line LP record disc synchronized televisor though never shared it at the time as it was for a secret ham radio club project. Anyhow I built the televisor using the NBTVA handbook circuits http://www.nbtv.wyenet.co.uk/beginners.htm . The set worked and did sync up though needed some coaxing and when playing motion videos did go off sync but still pictures and webcam without movement of the camera it stayed locked in sync. The record was of course hand drilled and accuracy of hole position was of course bad resulting in a cruddy crooked picture with unevenly spaced lines.

Fast forward to 2022 and I decided to order some manila Nipkow discs from NBTVA club and have converted the set from heavy record disc to light weight manila disc which was pretty straight forward. On firing up the motor spun too fast so I replaced the 10 ohm resistor with a 47 ohm resistor which fixed that issue. I had a variable LM317 power circuit connected to sync LED and motor boards which I had to tweak a bit to make the motor run close to correct speed. Anyhow the sync is semi working as it will occasionally lock onto sync after tweaking the LM317 power circuit but the picture will slowly bob up and down and go off sync after a while but often the picture doesn't sync. And when it syncs the picture is often offset too. Also adjusting RV1 on the motor board which I guess is a speed control or sync control seems to do absolutely nothing.

From memory I copied the circuits from the NBTVA handbook page mostly to the tee but for the opto fork sync system I am not using a TIL100 opto sensor but some sort of photodiode as TIL100s are not available at my local electronics store so I made do with a photodiode, the infrared light should be a LD271. I have taken scope readings from pins 3 (outputted opto sensor signal input), 13 (output to motor circuit) and 14 (sync input) and have photographed them which are attached to this post.

Anyhow I admit despite making mechanical sets since 2012, I am still pretty much a novice with only basic understanding of how the circuits work especially sync circuits and I call upon those more technically minded than me for help with getting this set synchronised. I would like to know what are the possible issues causing my set not to lock into sync? Could it be the positioning of the hole mask? Choice of opto sensor? The motor I'm using? The positioning of the opto fork relative to the LED matrix? Those wondering why I haven't light proofed the opto fork I do test the set in very low light too and it didn't make a difference in how it synced.

Anyhow I've made construction vlogs on this set which can be seen in the playlist link https://www.youtube.com/playlist?list=P ... vl6TkOzrus

Attached below are pics of the televisor and the scope readings
record.jpg

televisor.jpg

holemask.jpg

motor.jpg

sync.jpg

pin3.jpg

pin13.jpg

pin14.jpg
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Re: 32 line manila disc televisor project (sync issues)

Postby Klaas Robers » Thu Nov 17, 2022 3:53 am

The signal at pin3 is not Ok. I should see only the 31 upgoing pulses per revolution and not or almost not the black piece of tape once per revolution. It is possible that it occurs because the disc is slightly transparent, but more likely it is because there is room lighting that illuminates the surface of the disc.

You can improove this by painting the disc black at the side of the photo sensor, or placing a black paper ring on the photosensor, very close to the disc. That ring will obscure room illumination on the disc.

If your photo sensor is the "black LED", why did you place it so far from the disc? If the "black LED" is the IR LED, the distance is less a problem.

And then: Play with the resistor that is in series with the photo diode. In the circuit diagram it is R2, 1M. And look at the signal at pin 3 of the 4046. Adjust it such that the amplitude of the 31 sync pulses is as large as possible. And see that the "centre line", that is the line with equal distances to the tops of the 31 pulses and the bottom of these pulses, is at a voltage half way the ground and the supply voltage of the 4046. In that case the black sticker on the disc will be almost invisible in the signal.

But there is also something wrong with the signal "sync in" on pin 14. I expect there only the 31 sync pulses and not the large vertical pulse once in 15 (?) lines. But may be it is a trace 2 signal that you used to synchronise the oscilloscope.......

Now the 4046 can work as it is meant.

Good luck!
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32 line manila disc televisor project (sync issues)

Postby acl » Thu Nov 17, 2022 9:51 am

Hi there,

Several members have experienced the same problem with the manila discs. We used to use a material called darvic on earlier discs but alas this material does not succumb to laser drilling. The manila discs are geometrically superior although they do not block infra-red signals 100%. Like Klaas says reducing the 1 Meg resistor on pin 3 may help but all I did was place strips of black electrical insulating tape between each synch hole remembering to still cover hole 32,

Regards Chris Lewis G6ACL

IMG_3979.JPG
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32 line manila disc televisor project (sync issues)

Postby acl » Thu Nov 17, 2022 9:53 am

PS do not allow your soldering iron anyway near the manila disc.
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Re: 32 line manila disc televisor project (sync issues)

Postby aussie_bloke » Mon Nov 21, 2022 8:04 pm

acl wrote:Hi there,

Several members have experienced the same problem with the manila discs. We used to use a material called darvic on earlier discs but alas this material does not succumb to laser drilling. The manila discs are geometrically superior although they do not block infra-red signals 100%. Like Klaas says reducing the 1 Meg resistor on pin 3 may help but all I did was place strips of black electrical insulating tape between each synch hole remembering to still cover hole 32,

Regards Chris Lewis G6ACL

IMG_3979.JPG


Thanks for the information. I decided to cover the gaps between the holes with black tape myself, which resulted in partial success. The disc now is close to syncing properly and the pot on the motor control now works, what's happening now is the picture will sync but then it will bounce and eventually go off sync. I have uploaded a new vlog showing the latest update on my televisor https://www.youtube.com/watch?v=mwXhKecbXqk as you will see the picture is bouncing and the sync tips at pin 3 are also bouncing on the scope. I would like to know what is causing the sync to bounce?
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Re: 32 line manila disc televisor project (sync issues)

Postby Steve Anderson » Tue Nov 22, 2022 3:47 pm

Here's my tuppence...supplies clean? It appears you're using a DC brushed motor - they generate a whole lot of garbage that inevitably finds its way onto the power supply lines. If you're using one of the familiar DC-restorers to stabalise the video input these can display those symptoms as a result of high frequency crap on the power supply and/or the signal. The pulses can be very narrow and probably wouldn't show up at the speeds the 'scope seems to be set to.

Try placing a 10-100n disc ceramic capacitor directly across the motor terminals as a start. Maybe also generally bypassing all the supply lines with a mixture of the same type of disc ceramic caps and throw a few medium sized (100u) electrolytic caps at them too - it can't (or shouldn't) harm.

Also use shielded cable from the photosensor to the circuit. Maybe a small capacitor across the photosensor too, try 100p to start.

Try earthing the body of the motor, assuming it's not connected to either of its two power tags.

Let us know what the outcome is....

Steve A.

Try spinning the disc by hand (rapidly) with the motor disconnected...both mechanically (if possible) and electrically...
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Re: 32 line manila disc televisor project (sync issues)

Postby Steve Anderson » Tue Nov 22, 2022 6:59 pm

I would also add, place the photodiode (or whatever) amplifier right behind the device (in a metal screened and earthed box) so there is little chance of crap influencing the signal. To be honest a BLDC motor, although more complex, is the way to go...no brushes, no garbage....though you may still have to deal with the reactance, but that's a known quantity...

I don't know how many times I've promoted good bypassing, clean supplies, screening, sound earthing/grounding principles on this forum, why do so many ignore it?. All (maybe most) of my previous suggestions have, when applied, sorted the problems out. Keep earth/ground leads short and fat, use a metal chassis and screened cables. If you wanna keep the shit out of your signals, keep things small and compact and low impedance.

Yours frustrated of Bangkok,

This really should be piss easy...

Steve A.

...Later, sorry for the rant, but I hope some may listen...nearly 50 years (yep, I'm old) of experience should count for something...my avatar photo was taken when I was about 61-62...in February I'll be 67...(17th February 1956)...
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Re: 32 line manila disc televisor project (sync issues)

Postby aussie_bloke » Wed Dec 28, 2022 10:58 pm

Thanks Steve for the excellent tips and pointers, have made special note of it all. Sorry to add to your frustration, I do have learning difficulties as I'm on the autistic spectrum and I am bad at missing obvious things with my projects (which makes me feel like a total dumbarse) and I'm merely a hobbiest with basic electronics knowledge (though can construct very complex circuits copying schematics) so in this case I just copied the NBTVA club circuits and never thought into the noise factors at the time of construction. Anyhow I will now!

I've been corresponding with Richard Diehl of Labguysworld about my televisor issues, he told me he built a modded version of the club circuits which he found worked better for him and so I've decided to start from scratch and build his circuits http://www.labguysworld.com/NBTV_BigTelevisor_001.htm and will of course incorporate the bypassing/screening/grounding. I will change the opto fork from IR LED and photodiode to a bright LED and a NPN phototransistor which Richard strongly suggested. I admit my opto fork setup is pretty dodgy too no rigid correct positioning just hot glued and positioned as approximate as possible.

Will let you's know how I go on my rebuild.
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Re: 32 line manila disc televisor project (sync issues)

Postby Steve Anderson » Thu Dec 29, 2022 11:29 am

I'm not the only one who 'bangs on' about a particular aspect of circuit layout and good electrical/electronic practices. In a similar and related manner, Hans Summers (QRP Labs, https://www.qrp-labs.com/) goes on at length regarding power supplies. In summary he blames inadequate power supplies for the poor results some find of projects they build. He (and I) understand the reluctance of many to dabble in mains wiring to build a power supply, preferring to re-purpose a wall-wart phone or laptop charger or the like. They have to (or should) meet internationally accepted safety standards, though many are questionable in that regard.

Screening, bypassing, a good layout, and suitable power supplies can seem boring, tedious, a pain generally, but ignoring them is a recipe for a disappointing outcome in so many ways.

Steve A.
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