New NBTV camera project

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Postby aussie_bloke » Thu Apr 25, 2013 11:19 am

Ok everyone here's the latest updates on my NBTV camera/monitor.

Firstly I replaced the glowing 22k pot, stuck a good 20k pot in and no more glowing which is good. As mentioned the 400Hz clock is working good, on output I'm getting rocksteady 2.5ms square wave!

Then next was to do what Gary suggested, feed a NBTV signal to the monitor to accurately adjust motor speed to 750 RPM so from my MP3 player I fed a some NBTV files to the input of the video sync mixer circuit and up came the the NBTV pictures easy :) .

After getting the motor to around 750 RPM I then fine tuned the speed control to get as best as possible sync, then I adjusted the encoder disc circuit to see if I could get the sync locked in but no success. Now questions about the encoder disc circuit, the width of the negative pulse part of the wave form on scope, is that meant to be 2.5ms?

So yeah the sync is for some reason not working properly. During testing I have been wondering about some things. Having the encoder disc uncovered and exposed to any light I wonder if stray IR light is coming in from daylight coming into the garage, I know for a fact my 150W lamp emits IR light and was affecting the encoder disc circuit dramatically until I stuck a bit of wood in the way. Also distance of the IR LED/phototransistor from the disc, does it have to be a particular distance? And I am wondering too with the motor/disc spindle, there is a bit of time for readjustment of speed due to the momentum factor, would that upset the sync?

Anyways I have made a video log for you all of what's currently going on with my camera, in the video I have NBTV signal source plugged into the video/sync mixer board and I am demonstrating and talking about what's happening, the video is 15 minutes long so I had to upload it to Depositfiles as it was 118mb, you can download it from this link http://depositfiles.com/files/uyc2wmvz3 .

THOUGHT FLASH: Oh one this just occurred to me, looking at Harry's schematic of the main sync board, I notice there was a connection between pin 3 of the 555 timer and pin 3 of the 4046 but a then a couple of lines drawn over which I "assumed" as an indication of a wiring mistake so I didn't connect the pin 3s together, question for Harry, those 2 lines are they crossout of a wiring mistake or is it meant to be a capacitor? If so then there's at least one of my problems!

Anyways as promised here are all the schematics I used, some are from Harry's circuit sketches and some come from past NBTV club newsletters. Also in the pics below are the waveforms on the scope of what I'm getting in certain key areas of the circuitry:
Attachments
400hz-clock.jpg
400Hz clock circuit
400hz-clock.jpg (62.91 KiB) Viewed 8518 times
encode.jpg
Disc encoder circuit
encode.jpg (34.25 KiB) Viewed 8518 times
encode-sync-motor.jpg
Disc encoder + sync + motor speed control circuit
encode-sync-motor.jpg (67.43 KiB) Viewed 8518 times
speed.jpg
Speed control for high power motors that draw higher current
speed.jpg (76.07 KiB) Viewed 8518 times
sync-video-mixer.JPG
sync/video mixer circuit
sync-video-mixer.JPG (72.06 KiB) Viewed 8518 times
400hzclock.jpg
400Hz clock pulse
400hzclock.jpg (54.52 KiB) Viewed 8518 times
4046pin13.jpg
Pulse from pin 13 of 4046 going to fine motor speed control circuit
4046pin13.jpg (59.11 KiB) Viewed 8518 times
encodedisc.jpg
Disc encoder circuit output pulse
encodedisc.jpg (36.42 KiB) Viewed 8518 times
linesyncpulse.jpg
Line sync pulse coming from pin 3 of 555 timer going via resistor/capacitor to sync/video mixer board
linesyncpulse.jpg (44.66 KiB) Viewed 8518 times
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Postby Harry Dalek » Thu Apr 25, 2013 12:37 pm

aussie_bloke wrote:
THOUGHT FLASH: Oh one this just occurred to me, looking at Harry's schematic of the main sync board, I notice there was a connection between pin 3 of the 555 timer and pin 3 of the 4046 but a then a couple of lines drawn over which I "assumed" as an indication of a wiring mistake so I didn't connect the pin 3s together, question for Harry, those 2 lines are they crossout of a wiring mistake or is it meant to be a capacitor? If so then there's at least one of my problems!
:


Hi Troy

Yes its a mistake troy drawing the schematic thus the crossed out lines and put in arrows .
Sounds like a wiring mistake from my schematic .

Remember i have the lm311 and 555 on 5 volts ...i also think the PLL and crystal clock were on 5 volts to but my camera is boxed up in the shed to double check .

i did put in a pot where the 1meg feed back resistor is in the video sync mixer circuit ...

It sounds like you are pretty close Troy just a few things to check .
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Postby Harry Dalek » Thu Apr 25, 2013 12:43 pm

Troy i forgot last post

LM311 output gos to the PLL pin 3

and the 555 pin 3 to the video sync mixer input

The first is for motor control and the 555 is to make the sync pulse

The sync from the 555 timer gos to the 4,7k resistor in that video sync mixer circuit

Your head amp out put to the video sync mixer video input where that pot is
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Postby gary » Thu Apr 25, 2013 1:11 pm

Now questions about the encoder disc circuit, the width of the negative pulse part of the wave form on scope, is that meant to be 2.5ms?


No, that should be 2.5ms between leading pulse edges.

After getting the motor to around 750 RPM I then fine tuned the speed control to get as best as possible sync, then I adjusted the encoder disc circuit to see if I could get the sync locked in but no success.


Troy, if you haven't already done so, you should read through, and apply, Karen's brilliant tutorial on adjusting the motor speed controller in the last news letter.
Perfecting an NBTV system is like trying to slam a revolving door...
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Postby gary » Thu Apr 25, 2013 3:12 pm

Troy, having looked at the video, initially your encoder pulses looked very noisy - later on they didn't look too bad but it wasn't very clear - there appear to be oscillations around the pulse edges. The encode pulses should look, and measure, about the same as the pulses from the xtal oscillator (when the disk is in sync of course).

As the PLL is configured to only require a leading edge the width of the pulse is not really important but I think debugging is easier if you make the xtal pulses and the encoder pulses identical.

Again the measurement you are after is 2.5 ms *between* leading pulse edges - the way you measured it on the xtal output.

It might be an idea to have a look at the raw pulse before the 555 timer - at pin 3 of the lm311 and again at pin 2 of the 555.

A bit of a cardboard shroud around the ir sensor might be advisable - it is impossible to know the optimal distance for a home made sensor like that - trial and error is best but the closer to the disk you can get the better regarding stray light. Of course to be really close the LED and photosensor would need to be at an angle to each other.

Note that the raw pulse straight out of the sensor should have a 50% duty cycle - that is 50% positive and 50% negative.

I don't like the disk hitting against the screws at all - I can't see you ever maintaining sync with that happening - can you replace those screws with countersunk screws or something to lower the profile?
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Postby aussie_bloke » Sun May 05, 2013 10:39 pm

Okay, I have done a couple of mods to my NBTV camera since last update.

Firstly I have stuck a cardboard paper hood over the IR LED/phototransistor unit to shade the unit and the encoder disc from stray IR light from other sources so the encoder disc circuitry works correctly.

Secondly to keep the disc away from scraping against the bolt of the lens system I screwed a metal bracket into the support holding the disc spindle, pushed the support forward a bit and screwed the other end of the bracket into the base, so now it's not scraping against the bolt. It does however scrape against the LED monitor on start up but once the motor spins faster the disc no longer touches it.

Thirdly I have read over Karen's speed controller which was a good read and I have done a redrawing of the main sync controller board adapting her speed control to the schematic Harry gave me. Here it is below in the attachments, I would like some opinions on it about whether it would be effective or not with my motor. Also those two 4k7 resistors, should I use lower resistor values than 4k7s for higher current driven motors? And I notice with the circuit I used for the main sync board, pin 9 on the 4046 was not connected to earth, yet in Karen's speed control it is, would that be a possibility of why my camera might not be syncing?
Attachments
sync-speed.jpg
Main sync board with Karen's speed control circuit diagram adapted to it
sync-speed.jpg (64.27 KiB) Viewed 8456 times
bracket.jpg
bracket.jpg (67.81 KiB) Viewed 8456 times
hood.jpg
hood.jpg (50.5 KiB) Viewed 8456 times
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Postby gary » Sun May 05, 2013 11:01 pm

The two obvious *potential* problems you *may* have is:

1) the encoder pulse is going straight to the 4046 - as I mentioned to Ralph I have had problems with that in the past and recommend some pulse shaping - in truth I can't see why you can't just use the pulse coming out of the 555 or put in a Schmitt trigger like Ralph did here:
http://www.taswegian.com/NBTV/forum/vie ... php?t=1673

2) you have 32 pulse per frame coming from the xtal osc and 31 coming from the encoder - this will probably cause a problem but *may* not if the inertia of the disk is high.

Sorry, there are no hard and fast rules here because every implementation is different (disk size, motor types etc - even chip versions can have an effect). I can only advise on issues I have had to give you a "feel" for what can go wrong. Eventually if things aren't working we will need to see some 'scope traces - particularly at pins 3, 13, and 14.

Yes it is a good idea to tie pin 9 to ground.

Steve's "mania" on decoupling etc is also a very good "mania" to have.

Re the 4.7k - follow Karen's advice if you feel you need to "tweak" those values - i.e. maintain a balance between the two resistors.
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Postby Harry Dalek » Mon May 06, 2013 5:18 pm

Hi troy need to see whats coming out of your encoder circuit with your scope set so we can see all the pulse lines and seeing the missing pulse if the lm311 is not set right you will be getting mistake pulses you can only see this if you set your scope to view them all at least a disk rotation at once ...you should be able to count them one per line and there will be a gap for your missing pulse ..if there are random lines and such adjust the pot on your lm311....

If still no good use this scope setting to adjust the distance of your sensor to the encoder this is pretty much can give trouble if not set right....

Edit...i just looked back at your past post i see you have put whats coming out of the 555 timer looks like the amplitude is very wavy is it the same out of the LM311 and or the encoder photo diode ? if so i think you have a bit of wobble on that nipkow ....wonder if the increase and decrease of the signal is effecting your motor control ....
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Postby aussie_bloke » Tue May 07, 2013 6:11 pm

Thanks for the info, I will get onto checking it all out. Harry the record disc unfortunately is warped hence the brushing against stuff, also the encoder disc is not precisely centred even though I tried to get it centred so I wonder if that has a bad effect on synchronicity?
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Postby gary » Tue May 07, 2013 6:46 pm

aussie_bloke wrote:Thanks for the info, I will get onto checking it all out. Harry the record disc unfortunately is warped hence the brushing against stuff, also the encoder disc is not precisely centred even though I tried to get it centred so I wonder if that has a bad effect on synchronicity?


No, unless it was absolutely miles out it shouldn't have much effect.
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Postby aussie_bloke » Thu May 30, 2013 5:30 pm

G'day all.

Haven't been working on my NBTV camera/monitor in a while but some weeks ago I have made a telerecording of the camera in operation running at its own speed unsynchronized using my late 60s Concord NEI-17 B&W 1" vidicon tube video camera which with its vidicon lag characteristic makes the picture less flickery and no picture breakup like with CCD cameras.

I have already shared a couple of clips in my previous posts but here's a full 10 minute video which I've now posted to YouTube:
http://www.youtube.com/watch?v=ZY9mwXC--ro

I have put little pictures below left in the video for each object I placed in front of the lens so you know what's in front of the lens.
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Postby Naggara » Fri Jun 21, 2013 9:42 pm

aussie_bloke wrote:Thank you Gary for the templates and the program that does the 1.5 turn discs :) . Will definitely stick a masking in front of the disc to prevent light spillage.

To have an simple begin, you should have stored the ranges of the glide projector before you scapped it. Then restore it with the Nipkov disk at the place of the glide and the picture transistor at the place of the filament of the projector screen light. Then you need only little improvements for an maximum outcome.
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Postby aussie_bloke » Fri Sep 13, 2013 5:14 pm

G'day all.

It's been months since I last tinkered with my NBTV camera/monitor though have demonstrated it in operation to a couple of people since who were very impressed with it :) . Anyhow finally dusted it off and picked up where I left off.

I have grounded pin 9 of the 4046 chip and I have been taking photosnaps of what I get on the scope of the following:
555 timer pins 2 and 3
4046 pins 3, 13 and 14
I have taken a few snaps of some of the pins with the scope time period adjusted to see the signals closer particularly pin 13 of 4046. Also made a video of the unstable signal from pin 13 of the 4046 and a video of the encoder output while I try and adjust the motor speed and the encoder to get a duty cycle and period matching that of 400Hz clock, is that what I had to do, get the encoder output matching the 400Hz clock pulse? Anyhow if that's what I had to do as seen I couldn't get the encoder pulse to match the clock pulse. I am now wondering whether I have got the distance from IR LED/phototransistor to encoder disc wrong as I didn't do any precision testing on appropriate distance?

I am also going to read over Ralph's notes as well to clarify my understanding better of the sync circuitry and try to implement the Schmitt trigger as Gary suggested.

In the meantime here below are the pics and videos below to show what's going on, some of the scope readings I've posted before but here it is again:
Attachments
555pin2.jpg
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555pin3.jpg
555pin3.jpg (78.55 KiB) Viewed 6948 times
4046pin3.jpg
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4046pin3a.jpg
4046pin3a.jpg (67.69 KiB) Viewed 6948 times
4046pin13a.jpg
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4046pin13b.jpg
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4046pin13c.jpg
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4046pin14.jpg
4046pin14.jpg (70.75 KiB) Viewed 6948 times
encoderout1.jpg
encoderout1.jpg (56.5 KiB) Viewed 6948 times
encoderout2.jpg
encoderout2.jpg (65.03 KiB) Viewed 6948 times
4046pin13.avi
(835.82 KiB) Downloaded 332 times
encoderout.avi
(11.46 MiB) Downloaded 9730 times
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