Narrow-Bandwidth Television Association

So I have been working on my new Mechanical TV.

My Nipkow used to be spun using plastic gears. Today I changed that out to use a belt and a motor with much higher RPM. This method is indeed much quieter even though my video seemed to magnify the sound. I am pretty pleased with it now. My only concern now was that the motor now draws nearly 1 Amp on startup and settles to .4 Amp at speed. My previous geared motor never went above .3 Amp ever. I was concerned the MOSFET I am going to use RFP30N06LE would not handle this but I think I misread the data sheet.


youtu.be/wg4Fz27uLMQ

Currently, I am planning on using a Teensy 3.6 to drive the Audio and Video. After reading how Andrew Davie created his Televisor, it really opened up the possibilities with what could be done. He coded his with C on the Arduino. Not something I really wanted to do. So I figured the 180 Mhz for the Teensy would give me room to be sloppy and use Arduino language (Java).

I loaded the Doctor Who from his Get Hub onto an SD Card and was pleasantly surprised that I could in fact have an interrupt firing at 19,200 times a second with no issues. I passed the video half to a PWM port and the Audio half to a DAC. The sound from the DAC is horrible because I mainly suck at properly handling sound output.


youtu.be/D4jxTZRfxcI

I have a level converter to send 5v PWM pulses to a RFP30N06LE that drives the set of 4 1w LEDS. Seems to be working fine.

My only concern now was that the motor now draws nearly 1 Amp on startup and settles to .4 Amp at speed. My previous geared motor never went above .3 Amp ever. I was concerned the MOSFET I am going to use RFP30N06LE would not handle this but I think I misread the data sheet.

I can assure you that a 30A mosfet will handle a 1A motor very easily. Even without a heatsink.

I use a similarly rated MOSFET and my motor draws ~600mA continuously and I've run my mechanical set for 2+ hrs and the MOSFET only gets warm to the touch

Programming in C really isn't bad. Its worst learning for the performance an flexibility

Updated my sync wheel by adding 32 magnets on the other side to let me do a line sync. I was going to just have one sync magnet on the other side. It started not to make much sense for having just one sync per frame.



After spinning the new motor drive and syncs it appears I can easily keep 400 hz.

I have a bunch of CD4046's to attempt to make the video and motor track. Confused how that would keep the frame synch... just the lines.

Have to put the CD4046 on the breadboard to see exactly what happens when the motor is in sync (using frequency generator). I want to think the output from the CD4046 maintains a signal of what it took to get them into sync instead of just zerioing out when it is in sync. If it were to zero that seems in my head that the motor would slow back down. I really am not that good with data sheets honestly.

I have a bunch of CD4046's to attempt to make the video and motor track. Confused how that would keep the frame synch... just the lines.

It wouldn't. That's why the NBTVA standard has a missing line sync pulse every frame

I think I must have rocks in my head to have tried to use a CD4046. I put them up on the scope and really I can't make heads or tails of what it is doing. Seems to be mostly nothing. Maybe its sensitive rails as I read on some threads on this forum. This... this is why a programmer should not do things outside basic and obvious electronics and post schematics so people can laugh and point out obvious silliness... which warms my heart.



Now admittedly I didn't use Pin 7's cap to ground. I don't quite understand that. And I did not use the cap to ground on Pin 16. It all being on a bread Board that is probably a huge mistake.

thanks for listening.
Peter J. Fischel

Ok so as to not seem as pathetic as my last Post, I put the capacitors in on the power rail and from pin 2 to ground. I am really not seeing any difference.

My output from the CD4046 on pin 13 is the pink (channel 2)



I altered the motor RPM up and down to see if I could see anything useful an nothing really made any sense. I even put a 10uf cap on the output of pin 13 to ground to see if I would get cleanup. Nothing happend.

It's not easy to tell from the photo, but is the signal on pin 14 (SIGNin) 5V? (0-5V) in amplitude? From what I can see it appears to be only about 1V. Also I don't know whether you're using a x10 scope probe.

Also check pin 2, remove the 10nF cap and you should see something, probably an almost random unstable square-wave...at least that tells you you're getting proper logic level inputs to the device...not sure why that cap is needed, it's a logic output which isn't needed, delete that cap.

The output on pin 2 is from a simple ex-OR gate, if one (or both) of the inputs are not at proper voltage levels (ie. too low) you'll get nothing.

Steve A.

Yeah, it turns out I did have 10x on my probe. So I am sending 5v TTL to pin 3 from the 74LS04 inverter.

Removing the cap from pin 2 makes no change. Probing pin 2 after removing the cap the results seems to follow the signals.

Man I must be doing something so very silly. Look at this image...



omg the 5v rail from my breadboard supply is putting out 12v. WTF.

I cant believe my 74LS04 never popped with that voltage. No wonder the CD4046 is not working properly if its sees such a difference between the 5v and 12v.

I cannot believe my breadboard supply ... ugh.

So I fixed the 5V supply by running it from my Bench Supply.

The signals from the CD4046 look way different now. It makes me think the results go flat when they are in sync and have a wide pulse when too slow and short pulse when too fast. But that might be me making up a theory.


youtu.be/nqWqIddccn4

I am concerned that I might have ruined my Hall Effect Sensor. Seems not nearly as stable of a result by having a static voltage as I had before.

I dunno... the CD4046 might be a bit out of my league. I am used to putting PWM on the motor pins to get it up to speed. If the results are what I suspect I don't see how this would do much in that case. Maybe it would work if you were supplying a DC voltage you were altering with that output. But seems I would need to read the length of that pulse with a MCU and then alter the PWM accordingly. If I was to do that, I could just do it with MCU and bypass that chip.

Thanks

So I have been designing my new Hall Effect Adjustment mount.



In the bigger holes, there will be metal inserts to make a strong connection for M3 Screws. They get melted into the plastic.



On top of the standoff will be the arm where the hall effect sensor will sit. This should allow me to callibrate the angle.

Note to others... its better to put the holes in your disk instead of having to make another disk to synchronize everything. Oh well... live and learn.

FlyMario wrote:...omg the 5v rail from my breadboard supply is putting out 12v....I cant believe my 74LS04 never popped with that voltage..

"Ah! There's your problem" (Mythbusters). Well, at least the first one. I would replace the 'LS04 even if it appears to have survived the over-voltage. Its reliability has been compromised and could die anytime soon...probably just as you're trying to diagnose another problem, throwing another spanner (US wrench) into the works..

Steve A.

The output of the 4046 is somewhat weird to guys that are only used to digital circuits. The output can be positive (1), or zero (0) or tri-state (floating). This makes examining its working difficult.

To begin with: provide the output with a resistor (10k) to +5V, and a resistor (10k) to ground.
Then when the output is tri-state, your oscilloscope displays a voltage of 2.5 volt. That is better than without the resistors, because then tri-state and zero both give a voltage of zero volts and you don't understand it any more.

The functioning then is as follows:
- when both input signals are in phase: the output is 2.5 volts,
- when one signal lags in time, there are 5 volt pulses with the width of the lag,
- when that signal leads in time, there are 0 volt pulses with the width of the lead.

The 5 volt pulses should speed up the motor,
the 0 volt pulses should slow down the motor,
the 2.5 volt level should keep the motor on speed.

So at this point we are already more or less in the analogue world.

Oh thanks Klaas! That makes sense. I guess we would then use op-amps to detect the changes if we were to use them in a digital circuit.

Interesting. I have to think about how to proceed. They seem kind of fun. Not sure that I can really pull it off vs just counting the difference between the sync pulse and motor line pulses in a mcu.

You provided some great insight.
Thanks!

So this evening I put together a new sync wheel with much bigger magnets.



I created an adjustment arm and mounted a new Hall Effect Sensor. I was concerned that the 12v that shot through most of my circuit might have damaged it.



This arm sits on this mount to give me good range to align the sensor with the image holes on the disk.



As you can see from this video sync pulses from the Hall Effect Sensor are much more stable.

https://youtu.be/tcklZ72YWiE

Thanks!

Hi Peter
are you feeding the hall effect sensor direct to the 4046 ? i always have a Lm311 schmitt trigger before feeding the PLL ,always nice to have a led on both to view how its going even if you have a nice scope .
You used the same magnets i used on the 2nd drum build yours fitted nice in place much better idea to my go .
There's a bit of wobble on your sync disc it must be slightly changing the pulse width...i know this well as for a camera Nipkow idea it causes video lines not to line up a result a wavy video more than likely not so much a problem for a monitor but it must have some effect to every thing running true .
Nice gear nice design .