Baird System Baird Televisor NBTV NBTVA

• Click on the picture above to see a large picture (720 x 720) of a Nipkow Disk for a 32 line Baird Televisor.
• Print the picture from Netscape or Internet Explorer.
• Glue it to some card and cut around the black circle.
• Use a pin or miniature drill to make holes in the card where the dots are. Don't forget the centre hole.
• Get a miniature battery operated fan (as sold in tourist shops) and pull the fan blades off.
• Attach the Nipkow Disk where the fan blades were.
• Control the speed by powering the fan from a 3-volt DC mains unit, connected via a 10 ohm variable resistor.
• Get 10 or more hyper bright LED's (any colour).
• Connect them all in parallel.
• Connect the group of LED's directly to the Loudspeaker output of your computer's sound card.
• Play one of the Baird WAV files from this site, and view the LED's through the spinning disk.

If it all works ( ! ) you will now be watching genuine Baird system TV pictures on your own home made Baird Televisor !

Refinements and Alternatives
This is intended to be the simplest possible demonstration of the Baird Televisor. To make it even simpler you can :

• Use the paper printout directly without the card.
• Forget about the variable resistor, just brake the motor with your finger. Either way there is no synchronisation, so the picture will roll and spin - a proper system for synchronisation requires building an electronic servo control which would make the demonstration much more complex.

The light from the LED's needs to be diffused evenly over an area about half an inch by half an inch behind the disk :

• Try different kinds of cloudy plastic.
• An alternative is to use a magnifying glass lens in place of the diffuser.  Mount a single LED behind the lens at its focus, and the whole area of the lens will be lit, brightly and fairly evenly, when seen from directly in front.
• The light works much better if you put 3 volts d.c. across the LED via a 47 Ohm resistor, with the sound card audio applied across another resistor - see circuit diagram. (Use 4.7 Ohm resistors if using 10 LEDs in parallel.)

The holes in the disk should be of the right size.
The hole diameter should be 1/32nd of the width of the picture scan:

• You can estimate the right sort of size by eye.
• For more precision, measure the difference in radius between the inner and outermost holes on your printout, divide it by 32, and use a miniature drill of that size.

Click here for a high resolution picture (2610 x 2610) of the Nipkow Disk.
You'll need to save it to disk & use a graphics program like Paint Shop Pro to print it. Get Paint Shop Pro version 3 from www.jasc.com

NBTV Picture Files in Windows WAV Audio Format :
Right Click and "Save Target As..." to save to Hard Disk

1.Central Strip of Test Card F
 including the centre circle
 
 
 
 
 
 

2.Close up of Carol Hersee
in Test Card F
 
 
 
 
 
 

3.The letters N B T V
in a vertical column
 
 
 
 
 
 
 
 

Making the WAV file longer using Windows Sound Recorder:

The WAV file is much more useful if it's made longer by repeating the sequence of frames as follows:
Start Sound Recorder, this will be found in
c:\windows\sndrec32.exe or c:\windows\soundrec.exe
Open the WAV file.
Press ctrl c, then ctrl v.
This copies the wav file, then pastes it to the end of itself, doubling the length.
Do this 5 times, and you have quickly made the file 32 times longer.
Save the file. It will now run for 2 minutes 44 seconds, containing 2048 frames, and be 5 MegaBytes in size.

Alternatively, any WAV file can be made to repeat indefinitely in Windows Media Player.
Start Media Player, this will be found in
c:\windows\mplayer.exe
Open the WAV file.
From the Edit menu, select Options, and tick the "Auto Repeat" check box.

About the Pictures
The pictures were generated as Windows Bitmaps, then converted to WAV files on a PC using "Cool Edit 96" by Syntrillium Software, available from www.syntrillium.com

• Each bitmap was made to the NBTVA 32 line standard (Narrow Band TeleVision Association).
• The sync pulse height is 30 percent, 77/255, or 4D(Hex).
• The sync pulse duration chosen was 6/80 line period, 187.5 microseconds.
• The bitmap format chosen was width 80 x height 32, 8 bit monochrome.
• This results in a 32 line scan, with 2560 samples, bytes or pixels per frame.

This was converted to a WAV file at a sampling rate of 32000 samples per second:

• It produces 32000/2560 = 12.5 frames per second, and
• A frequency spectrum with a bandwidth of 16 kHz.

The sequencing of data in the Windows Bitmap has been carefully studied to ensure that the Baird pictures are:

•  The Right Way Up
•  Not Mirror Images
•  Not Sideways, ie they derive from 32 lines x 80 samples, not 80 lines x 32 samples

This ensures that they are compatible with the specification for the Baird and NBTVA systems where:

• Line Scan Direction is from Bottom to Top and
• Frame Scan Direction is from Right  to Left

The disk above is also made to this standard, and should be rotated ANTICLOCKWISE as viewed from the print side. If someone has the time to try playing these sound files into a proper Baird Televisor, I would of course be interested to know the results! 

Mail to stephen@sptv.demon.co.uk  with any comments or suggestions.

Links to other NBTV Sites
NBTVA Narrow Bandwidth Television Association
http://www.nbtv.org

BATC British Amateur Television Association
http://www.batc.org.uk

MZTV Canadian Museum of Television
http://www.mztv.com

Click below to find out
How to draw the Nipkow Disk with Microsoft Excel