The Medium band Television Monitor

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Re: The Medium band Television Monitor

Postby Harry Dalek » Sat Jun 03, 2023 11:36 am

On Thursday i fired up the monitor and got nothing took me a day and a half of testing to work out i had removed a connection for pins 5 and 6 last week So the High positive was open circuit to the CRT :roll: i recalled when i noticed i was checking back then if a voltage difference between the 2 connections would change results than just having them connected together i just didn't reconnect them to the CRT Astig connection .
Any case there's a new problem the 3BP1 is connected up and sort of working the problem is i didn't take into account both crts Cathodes are now connected , when i adjust the brightness control its not changing the beam cut off voltage .
Testing the meters ground on cathode and testing on the 558 transistor collector it should swing from 0 to 60 volts its just staying on 60v so beam on the 3bp1 is being cut off all the time no matter how i control the opto coupler
But funny enough both CRT control circuits hooked up does not effect the control of the original Larger CRT control circuit i can see the voltage control to the control grid is working .
If i remove the control grid 1K connection from the crt the 60V the 3Bp1 lights up fine as expected .
Now if i remove the 3bp1 cathode connection its crt control circuit and now test the opto brightness control view the result via cathode as ground and collector with my meter i now have correct voltage control ,so a bit of a catch 22 its working but not if i have both crts cathodes connected ...i have to get my head around why hooking both circuits up only effects the 3Bp1 version ....if both stopped working i would get it .
Might be some way around it i will look into it today .
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Re: The Medium band Television Monitor

Postby Harry Dalek » Sat Jun 03, 2023 1:32 pm

Replacing the direct connection with a 33k resistor between ZD101 and D101 and the cathode got it working again ,i have not tried the best value yet but got the beam control working on the 3Bp1 . i will put videos up later the focus is a touch off still need to adjust that a bit .
I am also getting the same effect on beam cut off as the larger tube where the beam moves on getting close to cut off so i suspect its the low AC on the deflection plates .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Medium band Television Monitor

Postby Harry Dalek » Sat Jun 03, 2023 5:54 pm

The deflection on the 3Bp1 not so impressive at 12 volts AC the other crt needs a lot less to deflect
Still a bit of work to go but at least i have something to tinker with to get voltages right on both crts ,i will work on a better focus on the 3bp1 next and need to check the High negative more than likely dropped a bit with feeding two CRTs which i can increase if need be .

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Re: The Medium band Television Monitor

Postby Harry Dalek » Sat Jun 24, 2023 12:43 am

Working on these monitors had little time of late but gave me some more time to think .
i am going to use Richards NBTV cathode ray circuit up to sync detection also looking at the video modulation but modified for my one of my CRTS later on stage 2 over 100 line but will be using Steve's ramp oscillators and deflection amplifiers here should take care of the NBTV side of things
https://www.labguysworld.com/NBTV_CRTelevisor_001.htm

youtu.be/vYyjg64XDpc
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Re: The Medium band Television Monitor

Postby Harry Dalek » Sat Jun 24, 2023 4:26 pm

I have had no problems with Richards NBTV monitor circuit but up to frame detection or missing pulse i have stuck a problem ......it could be 2 things i have been testing on a dual 12v supply where the circuit uses a dual 15v supply .
I was also thinking the Non Polarized cap C19 used across Q1 as mine was marked NP not BP but checking "german caps often use Bp = bipolar - in english Np = non polarised." so that should be fine

The 555 used by Richard is a LM555 i have been using NE555 to test i am going to have to search my supplies of this timer and see if i have at least one LM555 to check some may say they are the same plug in replacements but not so


One of the most notable differences between the two ICs is the use of current mirror active loads in the LM555.

Despite being 'pin-compatible, the LM555's modifications cause the circuit to act very differently than the NE555.

We can see from the internal design that the LM55 uses active loads instead of fixed resistors. One of the most significant advantages of switching from resistors to active loads is that output timing is less dependent on temperature and supply voltage.

Another difference is that the trigger signal is prioritized in the original NE555, whereas the threshold signal is prioritized in the LM555. When pin 2 (trigger) is less than 1/3VCC, the output of a 555 timer is high, and when pin 6 (threshold) is greater than 2/3VCC, the output is low. The output of the NE555 is low if the trigger pin is low while the threshold pin is high. The output of the LM555, on the other hand, remains low even when the trigger pin is low, and only becomes high when the threshold pin is low.

Additional undesired pulses have been reported on the LM555's output, which could be related to the various priorities assigned to the threshold and trigger pins.


Trying a few versions of the NE555 i have found pretty much getting diddly squat out of it so will report back when i find a LM version to test

Because there may be slight differences and improvements between components from different manufacturers, believing that the identical part from a different manufacturer is totally 'pin-compatible' is sometimes incorrect. It is always a good idea to test chips before using them in a specific application.
https://components101.com/articles/lm55 ... -timer-ics
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Medium band Television Monitor

Postby Steve Anderson » Sat Jun 24, 2023 6:05 pm

Yes, sometimes there are subtle differences between manufacturers of supposedly the same device, if you can find the datasheet from the manufacturer that makes the chip in your hand, the better. In the vast majority of cases it probably makes no difference, but these pit-falls are there to trip you up. It shouldn't be so, but here we are...

I've not been caught out by this 555 version, but I so rarely use them that's no surprise. The early versions of the 555 used to put a huge but short current pulse (100s of mA) on the supply line, upsetting other logic using the same supply. This was 'designed out' which may explain some of the foibles between examples from different manufacturers and production dates. The difference between a bipolar and CMOS version can also be quite large, yet they are often considered, "just a 555."

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Re: The Medium band Television Monitor

Postby Harry Dalek » Sun Jun 25, 2023 12:13 pm

Steve Anderson wrote:Yes, sometimes there are subtle differences between manufacturers of supposedly the same device, if you can find the datasheet from the manufacturer that makes the chip in your hand, the better. In the vast majority of cases it probably makes no difference, but these pit-falls are there to trip you up. It shouldn't be so, but here we are...

I've not been caught out by this 555 version, but I so rarely use them that's no surprise. The early versions of the 555 used to put a huge but short current pulse (100s of mA) on the supply line, upsetting other logic using the same supply. This was 'designed out' which may explain some of the foibles between examples from different manufacturers and production dates. The difference between a bipolar and CMOS version can also be quite large, yet they are often considered, "just a 555."

Steve A.


Yes not all 555's are the same i also tried HA17555 in the circuit had no luck with that, its also a bipolar transistor version of the 555 like the LM555 i can see the timer in Richards circuit looks to be hooked up as a Schmitt trigger i think
I will just double check every thing check with Richard and if need be make it work .
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Re: The Medium band Television Monitor

Postby Steve Anderson » Sun Jun 25, 2023 3:43 pm

In 2010 I put together a different method of detection and regenerating the NBTV 'missing' sync. I think it appeared in the newsletter, though I'm not 100% sure.

The 'scope screen-scrape below shows the input video signal at the usual 400Hz line rate (yellow), the usual sync detection output (cyan), the generated frame sync derived as an average of the previous 31 sync-to-sync durations (magenta), and the previous two waveforms combined to form continuous line syncs (green).

Fig 4B Colour.jpg
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The re-generated frame sync is deliberately slightly narrower than the usual line syncs, there is/was a reason, but I can't remember why! It was 13 years ago!

Later... I've just re-read the article, the regenerated frame sync is narrower such that it can be used also as a black level clamp pulse. The 'missing sync' is the only place in the NBTV waveform that is definitely at black level. So it's the only place black-level clamping can be done. It's narrower to allow for the video rise and fall time. It's a shame that a back-porch was never allowed for, but with the limited bandwidth it's no surprise!

It uses a few more chips than just a couple of 555s, but it works well from a line rate of less than 300Hz to more than 500Hz without any adjustment required, i.e. automatically...

It uses...

1xPIC12F629 Microcontroller
2xLM358 dual op-amps
1x74HC4066 quad analogue switch
1x74HC02 quad NOR gate
1xLP2950-5 +5V regulator
1xBC547

Current consumption is around 3.2mA.

Steve A.

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Re: The Medium band Television Monitor

Postby Harry Dalek » Mon Jun 26, 2023 4:34 pm

Steve might have the code for the Pic one post back , i think this chip is programmed.
Have to say for syncing if you have the parts the circuit here with the 4538s monostable works very well not only for standard NBTV but a range systems i have tried any thing that will fit in the PC sound cards bandwidth so 15 line to 240 and 2 hz to 50hz tested but make sure they are HC type.
I am just going with Richards this time as i wanted to try it out .
Richard Videolabguy got back to me he thinks the NE555 should work fine and thinks the problem i am having is some thing to do with the transistor Q1 or the capacitor ,also mentioned the dual 12v supply i am using should work fine as well ...so i will have too look into changing parts and redo testing around there .
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Re: The Medium band Television Monitor

Postby Steve Anderson » Mon Jun 26, 2023 5:50 pm

Harry Dalek wrote:Steve might have the code for the Pic one post back , i think this chip is programmed.


Yes, it will need programming, though I don't think I've published the code anywhere, not as I recall anyway...(see next paragraph)...

You know, I do not remember drawing up that previous diagram! OK, it is definitely me, it's my 'style' and with my name, but I have no recollection of drawing it! Senility, it creeps up on you! I would have to reverse-engineer something I did to understand what's trying to be accomplished! Grey cells atrophying? Quite possibly/probably!

As for the 12F629 I can program a couple for you (and Richard too if he's interested) and send them on, they're as cheap as chips. (The edible variety).

However, without re-visiting Richards channel and finding the correct video, was his frame-rate 12.5 or 15Hz? The only difference would be some of the timing constants in the software...

However I would need to find the prototype and confirm all works as before, I've (probably) still got it here, somewhere! It's also one way to test any chips before I send then on...

Steve A.

Later... I've found the prototype (as in the photo above), it should work, maybe, it's been well over a decade since the last time it was powered-up.....I don't recall how I programmed the micro as there's no programming connector on the prototype, but that's my problem...
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Re: The Medium band Television Monitor

Postby Steve Anderson » Mon Jun 26, 2023 7:49 pm

Found the latest version of the software I did over a decade ago, summary follows...and this is for what is a small micro...

MEMORY USAGE MAP ('X' = Used, '-' = Unused)

0000 : X---X----------- XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXX-
2000 : -------X-------- ---------------- ---------------- ----------------

All other memory blocks unused.

Program Memory Words Used: 113
Program Memory Words Free: 1935


Errors : 0
Warnings : 0 reported, 0 suppressed
Messages : 4 reported, 0 suppressed


Steve A.
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Re: The Medium band Television Monitor

Postby Steve Anderson » Mon Jun 26, 2023 7:57 pm

Having problems copying photos out of my (newish) Android phone into Windoze 10, a pain, why can't we use something simple like Widows Explorer, drag and drop files (from one place to another?)...The phone should simply look like a hard drive...surely? My other drives do...D: E: and F:...

...seems like I've found out how to extract photos from my phone now. It's easy but not intuitive...plus a mix-up on the colour of USB connectors signifying speed of connection...which I have not had to pay any attention to previously...

https://www.usbmemorydirect.com/blog/usb-port-colors/

Here's how that small board looks today...most of the chips, aside from the micro, wouldn't be needed as their equivalents are generally within existing circuits.[1]

Found It 1.jpg


[1] Added later...as an example taking Richards circuit above, the micro alone could replace U2A, Q2, U3, U4, U5A, U7, and possibly U5D and U5B plus all the associated passive components...some earlier passive component values may need adjustment...not that many though...

I also referred to my notes, the prototype was quite happy with any line-rate from 270 to 520Hz, but of course it must be 32 lines with only 31 sync pulses...the math the micro does internally depends on this...it measures the time from sync pulse 1 to sync pulse 31 (30 line durations) and divides this by 30 to get an average line duration. It waits for that calculated time after line sync 31 then adds in that 'missing sync' aka a frame pulse.

Steve A.
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Re: The Medium band Television Monitor

Postby Harry Dalek » Tue Jun 27, 2023 4:26 pm

Steve Anderson wrote:Yes, it will need programming, though I don't think I've published the code anywhere, not as I recall anyway...(see next paragraph)...

You know, I do not remember drawing up that previous diagram! OK, it is definitely me, it's my 'style' and with my name, but I have no recollection of drawing it! Senility, it creeps up on you! I would have to reverse-engineer something I did to understand what's trying to be accomplished! Grey cells atrophying? Quite possibly/probably!


Its a few years now since you drew it up understandable i can go a few weeks and wonder how i wired up something ,,,memory is some times not forever it fades .

As for the 12F629 I can program a couple for you (and Richard too if he's interested) and send them on, they're as cheap as chips. (The edible variety).

However, without re-visiting Richards channel and finding the correct video, was his frame-rate 12.5 or 15Hz? The only difference would be some of the timing constants in the software...


I am pretty sure its standard 12.5 as we were just talking about the frame rate and that 555 missing pulse detection circuit yesterday .

I would try it out for sure if you come across one i am not sure Richard would try as he more i only do my own stuff sort of guy where as i don't mind copying good circuits .

However I would need to find the prototype and confirm all works as before, I've (probably) still got it here, somewhere! It's also one way to test any chips before I send then on...

Steve A.

Later... I've found the prototype (as in the photo above), it should work, maybe, it's been well over a decade since the last time it was powered-up.....I don't recall how I programmed the micro as there's no programming connector on the prototype, but that's my problem...

[/quote]

Oh thats good some times things go missing ! I see 4 capacitors that might might age but never know with those things .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Medium band Television Monitor

Postby Harry Dalek » Tue Jun 27, 2023 4:28 pm

Steve Anderson wrote:Found the latest version of the software I did over a decade ago, summary follows...and this is for what is a small micro...

MEMORY USAGE MAP ('X' = Used, '-' = Unused)

0000 : X---X----------- XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXX-
2000 : -------X-------- ---------------- ---------------- ----------------

All other memory blocks unused.

Program Memory Words Used: 113
Program Memory Words Free: 1935


Errors : 0



Warnings : 0 reported, 0 suppressed
Messages : 4 reported, 0 suppressed

Steve A.[/quote]

Is thats all the code ? not much too it its all over my head i am guess there are more lines to it !
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Medium band Television Monitor

Postby Steve Anderson » Tue Jun 27, 2023 5:06 pm

Harry Dalek wrote:Is thats all the code ? not much too it its all over my head i am guess there are more lines to it !

Nope, that's all it took, 113 'words', as you can see it only used a small portion of the available program space, about 5.5%. The biggest single 'chunk' is the divide 16-bits by 30 routine, only 31 'words' in program memory, simple straight-line code, no loops, i.e. fast. 1us instruction time, so done in 31us. Error 0.39%, good enough for this...

Clear store.
Divide input by 32, shift right 5 times, store.
Divide input by 512, shift right 4 more times, add to store.
Store = 1/32 + 1/512 = 16/512 + 1/512 = 17/512 = 0.033203...inverse = divided by 30.1176...near enough! You could take it further if you needed or wanted to, but here, not really necessary...simple binary arithmetic...even if I can't spell it...remember, micros, of all sorts HATE division...this is a simple method for division (or multiplication) by a constant...though it takes some time...even though straight-line code (no loops, calls or subroutines)...

Some 16-bit and higher micros do have dedicated divide 'cells', but I've not strayed into that territory, yet...

Steve A.
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