Narrow-Bandwidth Television Association

I have been itching to have a go at holtzmans 2 drum monitor ,i don't think i am as good at constructing as fine looking montitor holtzmans ended up as you see so far but i will give it a shot at trying to repeat the 2 drum idea .

I think holtzmans used black tape for the lines ,i tried it with what i had and found my stuff let light pass black or not ...next idea was hot glueing cut up strips of video tape but found again the stuff lets light pass only good on 2 layers thick seemed a bit to much work ..i ended up trying and using very thin cardboard the stuff is light proof .

Perhaps with the light levels of a modulating led array or a few luxeons the first two ideas might be fine but just went for the cardboard for now since it even stopped a laser ..I used clear tape to hold it all tight after gluing the cardboard looks a little messy ,if it shows promise i will redo them nicer ...i am more interested to see what happens more than pretty at the moment ...

Harry, you are nothing if not prolific - good luck with this one, it looks good.

Perhaps aluminium tape might be the go?

gary wrote:Harry, you are nothing if not prolific - good luck with this one, it looks good.

Perhaps aluminium tape might be the go?

Hi Gray Yes i am sure that would be good but i just used what i had and before i go shopping i like to try things out but yes i will keep that in mind if i do a better drum ,Its more of a test drum or drums than any thing for now to see if i can do it ...also sort of learning how to do the line strips ....

Yes Gary can not help my self i do skip from this to that,one thing leads to another...

harry dalek wrote:Yes Gary can not help my self i do skip from this to that,one thing leads to another...

Harry, don't in any way shape or form take my comment as criticism, I am much the same myself, this hobby, IMHO, is all about exploration of the technology - perfection is for squares -

Fascinating work! Good luck with this - I'll be following it with interest.

Steve O

gary wrote:

harry dalek wrote:Yes Gary can not help my self i do skip from this to that,one thing leads to another...

Harry, don't in any way shape or form take my comment as criticism, I am much the same myself, this hobby, IMHO, is all about exploration of the technology - perfection is for squares -

Gary no worries ,i think i am also a bit worried these days as the eyes are not what they used to be get it all in while i can i say !

Have to say holtzmans monitor is very impressive and dual slit drum or slit discs are rarely talked in early television about ,to see one working makes me want to try and repeat the idea.

Yeah the eyes - I now wear bifocals and I swear they make me clumsy as the eye crosses the boundary and the apparent distance of the object I am handling changes - damn!

Panrock wrote:Fascinating work! Good luck with this - I'll be following it with interest.

Steve O

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Thanks Steve never know till you try
Maksim has been very helpful with advice about he's monitor so i am half way there just knowing how he's works .

Details about the drums Size wise and such are if i have got it right holtzmans and mine 16 slits large drum 6 small...so 32 lines double line speed.
holtzmans drum large drum is 76.8cm round small 24.5 mine at the moment is 79.5 large small about the same .....
So line slit distance between slits on the large drum Holtzmans 47.8mm and small 40.8mm or 48 40..between mm is beyond my sight.
Mine is about 50mm large drum 40 small....

If i got it right with a line thickness of about a mm gives an aspect ratio screen size of 32mm across and 50mm high.

I was going with a smaller drum at the start but worked out that the drum would not give the aspect ratio for nbtv 32 line more like a square at 1mm per line so there is a limit to smaller drums i think.

Had a bit of a play with a 2 drum speed idea.

I am trying a control via a LDR and light pulses via 16 trigger signals( seems to run smoother on that and a white led this triggers a monostable ...now i was going to use a stepper motor for this project but am trying a geared dc out of a printer ...so the monostable is feed to a 7474 then a H Bridge L293 motor dual motor control IC ...since i am only trying the DC at the moment its only using half the ic .

To be Honest i have no idea what the speed of the second drum should be ,i might just go with it do a signal light test and see ...mmmm

The Dc seems to work once up to speed ,,,its not as neat as the stepper motor idea but just seeing if it will work ..

Heres some photos of a run test and some videos ...if you think i am doing it wrong just say i don't care i like learning ..from a look today looks to me like i might be close .

Hi there,
your machine looks promising. The small drum speed must be 1/12 of the large one's, if you use 6 slits on the small drum. The challenge is that drums should be deadly "geared" to each other. So using DC motor is not a starter option, and I can not understand how it is controlled by LDR loop... Take care of your fingers, the LDR interrupter looks frightening a bit

holtzman wrote:Hi there,
your machine looks promising. The small drum speed must be 1/12 of the large one's, if you use 6 slits on the small drum. The challenge is that drums should be deadly "geared" to each other. So using DC motor is not a starter option, and I can not understand how it is controlled by LDR loop... Take care of your fingers, the LDR interrupter looks frightening a bit

Hi there The small drum drive using the Dc motor i normally would not use but since it is geared ,(i think it was used for the movement of a scanner on top a a late model printer) ...i found if you pulse it it seems to act a bit like a stepper motor so i was thinking perhaps using 4 LDR's to control the speed direct to the mosfets H bridges as you did perhaps one could do the job via a monostable controled by it and changing the pulse width or my slots might fine tune it as your light slots distance for the LDRS ......My non understanding is the pulses for a start to the LDR number and length ...i tried just 4 sort of your number or the H Bridges but i found it ran smoother the more you put..so tried one for each line ....it speeds up slows down to the large drum speed ,its a bit ruff at the start but at speed it seems to run ok....
Just an idea i was wondering about and had the motor handy .
I will swap it if it does not show promise .Your stepper motor idea is for sure better and runs smoother .

Working out a Quick light to modulate for the Monitor, i am not going to be able to work out if the small drum with my control idea works unless i do .

6 watts should help a bit ,i have enough high bright white leds but will try these Stars first .

My drums 6 slots should be the defuser but not sure if the spread of the Luxeons will cause a light level drop in the middle ...well i'll find out soon .

So today just be testing it before i bolt it back on.

Just tested it knocked back the power for the camera wish i did that for the first test near on blinded my self
Heres the pwm circuit in that box if your wondering apart from the lm317 and a mosfet for the luxeon.

Hi Maksim
as we were talking heres a look at the redesign of the small drum motor ..for others i did the 2 drum test and found the Dc motor just runs to fast for the correct speed of 12 rotations of the large drum to 1 of the small...
So i have listened to Maksim and gone stepper motor for the small drum .
I am using a 5 pin stepper called unipolar Maksims using a 4 pin bipolar..
Also have to make a correct diffuser and see if my luxeons are running correctly wouldn't mind stick a row in the middle if i need more light ..but Maksims was saying i should be right ...
So a bit more work just sharing where i am at .

Hi had not much time of late to work on this but back at it ..i
Wanted to get stepper motor part working right had a bit of trouble with the driver part ,Using a uln2003 this works fine with all my unipolar steppers.

The one i am using has a nice speed range and works at the top range of my clock circuit without stalling so i think it has the speed range now .

I have also changed the gear idea for a direct drive meaning the motor can run slower ,i does not have much weight to move so torque not a problem.

I would still like to try gearing the main motor drum to the small one electronically I know Holzman made sort of a flip flop circuit with the LDRs and leds via a mechanical light switch...i would rather do this via electronics and just using perhaps one trigger via the big drum and adjust trigger pulse length electronically to adjust the stepper to the right speed ....

Well if all else fails all i have to do is sort of copy Holzmans working idea but since i am using a unipolar stepper they just need 4 trigger pulses in a row ...got to try ideas out or you never know !

So what you see i will hook up again to the main drum ...

I need to work on the light part of it again i am not sure if i will go with the luxeons as i was thinking i trying my green laser without or misadjusting a lens to spread the beam which i know works ,its very bright...be interesting to try both.

let you know how it gos

Congratulations for your working gear! I must say this is something I could not build right now as I do not have experience with ICs and flip-flops. And i still do not understand completely its working principle.
If i got it right, the drum makes 1 pulse each turn, and electronics provides other 3 in sequence? If so, you may have some problems on start because the frequency is different. And you have to adjust very fine your circuit in order to get continuous pulse sequence at the right speed of 12.5 fps.
I am going to a short vacation tomorrow so won't be here for a while sorry...