Narrow-Bandwidth Television Association

Named thus as NipKOW scanning is displayed upon a LAPtop.

I am making 2 versions.
The original idea with distortion problem, using the 2 mirrors which will scan at NBTV frequency and higher.
The other with rack and pinion frame drive as per Cambridge type.

Both to display on laptop. On the former design I hope to have moving
pictures as the frame scan rate can be very high.

Have spent much time trying to get the ADC to work.......
Due to my ignorance in all things electronic, the digital o/p from the ADC was being sunk
to zero volts by the laptop printer port inputs.
I thought it was my ADC wiring and rebuilt it TWICE!
Now about to buffer input to drive the printer port. Awaiting delivery of buffer.

All the mechanics work OK. A lot of work now required on the laptop program.'
I shall run the machine as I write the software and so see directly on the screen
scanning problems at all line and frame rates etc.
This will be the most interesting part, methinks.

Printer ports are a pain. As originally conceived there were 8 output lines and (I think) 5 input lines (paper out etc). This was called the Standard Parallel Port (SPP) mode.

Then came the possibility of the 8-bit port being bidirectional. The Enhanced Parallel Port (EPP mode).

Later still the Extended Capabilities Port (ECP).

This link I used some years ago and is still valid...at the top is 'Legacy Ports', all three modes of LPTs and covers RS232 if you ever need it.

http://retired.beyondlogic.org/ecp/ecp.htm

...and the information is all correct as I used it for my early PIC programmers.

You may need to dive into your systems BIOS settings to set which mode you wish for the LPT.

Steve A.

Hello Steve,
Thanks for all that and the link.
Fortunately my old Dell laptop printer port is ECP and is bi directional and inputs OK
using the right coding.

I didn't have to get into BIOS.

The buffer arrived yesterday and I'm pleased to say the ADC now works OK and inputs the 8 Data bits into the laptop.

I did previously do a lot of searching about the printer ports and can now also input into all the other port pins too
such as select/ACK/error/paper out/etc.
There are 9 usable input lines available in addition to the 8 data pins, so I have plenty to choose from for sync.

As you say printer ports are a bit of a pain, but much of NBTV is too.

Albert, it seems like you're on top of it.

For many (including myself these days) PC's don't have these lagacy ports. But FTDI based in Glasgow provide 'cables' that are active and turn a USB port into a virtual COM, LPT or UART port. I have used a few of their USB-RS232 'dongles' with complete success.

Usually the COM port becomes COM3 and/or COM4, the version I have is a dual RS232 I/O. I would think that the LPT versions work much the same...but I haven't tried them.

The 'cable' part of their site is here...the drivers are easy to install and free from the website...

http://www.ftdichip.com/Products/Cables.htm

Albert, you may not need them, but others might.

Steve A.

...looking closer, it seems like they've deleted the LPT 'cables'...

Yes, modern PCs only have USB now. For the home experimenter it is like most things these days,
"Improvements for the worst."

I have read somewhere on the net that in trying to convert USB to parallel
the BASIC emulator doesn't work.

So for me, it was best to buy an old, cheap laptop with parallel built in,
providing it's bi lateral of course.

I suppose I could have gone serial but I like to see
all those 8 DATA bits dancing merrily away.
So easy for me when testing, to see which one might be missing.

Thanks for the link, anyway, Steve.

There's a company just a few km down the road from me that makes all sorts of USB-to-whatever-you-wish devices. Futurlec (I think that's the correct spelling) in Australia are one distributor of their devices. If you look at a lot of the Futurlec stuff on offer it's often made by ETT here just down the road (examine the pictures of the PCBs closely). Buying it locally it's a bargain! They have a retail shop on the premises. But for one reason or another I've never needed to buy anything from them!! Though I have been tempted just for the 'toy' factor.

Steve A.

Still making good progress but have been thinking ! ............

Suppose there were two lasers about 4 inches apart with line and frame scanning coupled
to both. They could both be green lasers.
Only one scanning at any one time, switched alternately very rapidly.
(I would have to check to see how fast a laser can be switched on/off.)


With a change to my laptop program I could relatively easily make alternate pixels
input from each laser in turn, one plotting in red on the laptop screen
and the other in green on the screen.

Of course, the effective number of pixels per line would be halved,
but as I am aiming for a highish pixel rate it may not matter so much.

Then by wearing an old pair of red/green 3D glasses, Bob's yer uncle!

FWIW here is my demonstration of a test card played out of an LPT port into the AV of a PAL TV using a 2 resistor "DAC":

https://www.youtube.com/watch?v=tW822Yv6b4s

I like your 2 resistor DAC, Gary. If only ADC were as simple.

BTW, on another tack, anyone thinking of experimenting scanning with a green or red laser
should remember that it will distort any coloured scene quite badly !

This is because a green laser will be reflect less when scanning the red part of any object
as against when scanning a green part, resulting in false intensities of the reflections.

This is not a problem for me as the Lapkow is all experimental anyway.

There are yellow lasers which may fair better, but at present they are very pricey. (£150 plus!!)

Maybe I shall invest in an electric arc as the light source.

Viewmaster wrote:I like your 2 resistor DAC, Gary. If only ADC were as simple.

Actually it is - they are kind of symmetrical, and as imperfect.

I wonder if this will work?

With my laser scanning the solar cell will pick up extraneous light if
scene etc is not in complete darkness.
This means that my wanted video signal will be imposed upon a
constant DC voltage.(extraneous light).

So I plan trying to use an op amp as a voltage comparator.
One input will be the solar cell o/p and the other, adjustable
DC volts via a pot.

So the o/p should be solar cell volts minus DC volts setting via pot.

The pot volts can be slowly increase until the extraneous light volts
are nulled out.

It sounds OK but will it work?

Yes, it does work !

For anyone interested in my progress (or otherwise!)..........

A red laser gives a much stronger signal on
my solar cell than the green one did. Obvious I guess,
if one thinks about it.

Further, I found that some ADCs require a sample and hold circuit whilst they
are converting.

So I chose the ADC0820, which has a built in sample and hold.
But it only works if the signal doesn't swing greater than 1mV per micro sec so
we shall see if the varying laser i/p to it is within that spec.

Also about to connect the machine to the laptop so the program should
begin to run as the sync pulses are sent to it.

I might even see my first picture soon.
Then the debugging can really begin ! Beta, beta, BANG!

Great news Albert look forward to the tests.

Working on the auto speed adjust on program which is proving a bit of a pig.
The drawing line speed on the laptop must lock to the line scanning speed, of course.

Probably incorrect flag settings for start and end of line scanning/drawing.
The frame drawing locks well for quite a wide range of frame scanning
speeds so we shall see if I can get the line to behave too.

A picture, of sorts, is displayed on the screen but not line locked yet.
Looks like a static version of a non synced NBTV picture

Batteries for the laser are being used up as it all has to be running
whilst I work and continually try out the program.

I tried connecting the 3v laser to the USB supply with a series resistor but
no success so far.

Had a rethink on line sync.
Pulses are available at both line and frame starts and finishes.
The frame sync is latched with a latching relay so can be read at any time
in the fast running program, but the very short line sync pulse is not.

I think this why the prog can miss it. So am going to try
a set/rest latch using 2 NOR gates.
The gate will be set at line start and reset at end of line so
hopefully it will be read at EVERY line start/finish.