Baird Colour Televisor Use Stereo audio & different colours of LED to see Colour pictures on the disc.

Red / Green
Can produce any colour between Red and Green, including Orange and Yellow.

		BBC Eye
Left Channel Right Channel Red LED Green LED
		Right Click and "Save Target As..." to save to Colour wav file to Hard Disk

Orange / Bluegreen

		BBC Test Card
Left Channel Right Channel Orange LED Bluegreen LED
		Right Click and "Save Target As..." to save to Colour wav file to Hard Disk

The Orange / Bluegreen system works in exactly the same way as Red / Green, but it can produce a more realistic range of colours, including Fleshtones and White.
The Orange channel was produced by mixing 67% Red with 33% Green.
The Bluegreen channel was produced by mixing 33% Green with 67% Blue.
The image above was produced by mixing the 2 images back together using Paint Shop Pro, and gives a genuine impression of the range of colour that can be achieved. The actual 32 x 48 pixel images were used, then anti-aliased to double size.

R G B for Multitrack Soundcards
Seperate wav files for Red, Green, Blue.
Copy and paste into a Multitrack Audio Editor such as Cool Edit Pro or Cubasis.

This system produces Full Colour but requires a Multitrack soundcard with 3 independent audio outputs.

R G B for Stereo Soundcards
Bluetone system 14.7 kHz

This system produces Full Colour from an ordinary Stereo source, but requires a frequency filter to seperate the Blue signal.

14.7 kHz was chosen because it is 1/3rd of 44.1 kHz, the CD audio sampling frequency.
For these wav files, the Picture Frequency is 12.53 frames per second,
and the Line Frequency is 400.9 Hz. There are 110 audio samples per scan line.

By comparison the other wav files use 32 kHz audio sampling, the Picture Frequency is 12.5 frames per second, and the Line Frequency is 400 Hz. There are 80 audio samples per scan line.

The Blue signal should be derived from the stereo difference via a high pass filter at about 8 kHz.
The Red and Green signals should be mixed together (or "mixed to mono") at frequencies above 8 kHz to eliminate the 14.7 kHz carrier while preserving full bandwidth.
Click here for a sketch of a simple circuit to drive Red, Green, Blue LEDs directly from the sound card, using capacitors to accomplish partial seperation of the signals. The circuit is NOT guaranteed to work, but should be treated as the basis for experiment.
Click here for a block diagram of a system which would seperate the Red, Green, Blue signals properly.

General Tips for successful results with a 2 Colour or 3 Colour Televisor:
You will need several LEDs of each colour, with different LED colours distributed as evenly as possible behind the diffuser.
With RGB in particular it is essential to make extensive use of variable resistors to set the d.c. offset for each bank of LEDs independently. For a simple constuction it is easiest to use seperate bias batteries for each colour, for example 3 x 2AA battery holders with a 100 ohm variable resistor connected in series with the output of each. These are easily obtained from Maplin in the UK ( www.maplin.co.uk ) or Radio Shack in the US ( www.radioshack.com ), as are the LEDs.

Baird System with NTSC Colour
32 Line NTSC. Colour Subcarrier Frequency 14.7 kHz

These files are included for anyone who would like to experiment with them. Decoding them would require construction of a complete NTSC decoder, or modification of a standard NTSC decoder chip to work with the much lower subcarrier frequency, much lower bandwidth, and much longer burst gate.

32 line NTSC wav files are just as easy to produce as any of the others. The process of converting bmp to wav lends itself easily to the job because colour bitmap files are "dot sequential" RGB, with 1 Byte Red followed by 1 Byte Green then 1 Byte Blue and so on. "Dot Sequential" colour is a close relative of NTSC, and is infact how the NTSC system originated. Simply applying the same bmp to wav conversion process to a 24 bit Colour Bitmap, instead of the seperate 8 bit Monochrome Bitmaps used elsewhere, generates an NTSC type composite colour waveform.

These audio picture files have 36 samples per scan line (36 Red, 36 Green, 36 Blue, 108 Total). The Picture Frequency is 12.76 Hz and the Line Frequency is 408.3 Hz. The audio sampling frequency is 44.1 kHz. I have included a "Colour Burst" which is the Yellow line in the "line blanking" period at the bottom of each picture. These audio files are Mono, since all the Colour information is contained in a single monochrome-compatible composite signal, as the case with standard 525 line NTSC.

Alternative methods of decoding for the Baird System with NTSC Colour:
Electronic Switching, and Striped Filter.

Electronic Switching:
This would work by switching the composite colour signal electronically to each of 3 seperate outputs in turn, in synchronism with the 14.7 kHz Yellow line reference, thereby "demultiplexing" the 3 colour signals. Or if you had burnt the files to a CD, you might "cheat" by taking a 44.1 kHz switching reference from inside your CD player.

Colour Stripe Filter:
This would work by using White LEDs and placing the filter in front of the disc. The filter would consist of almost horizontal stripes of Red, Green, Blue, there being 36 groups in all. The stripes would not actually be horizontal, but lined up along radii from the centre of the disc (see picture). It would require EXTREMELY accurate phase synchonisation of the motor to within less than 1/10 th of a degree per revolution over long periods. The filter could be produced by simply printing out the picture of the filter here, onto inkjet printer transparency paper. Print size should be adjusted to match the size of the picture scanned by the Nipkow disc:
Right Hand Side Height = Distance between the 2 outermost holes
Left Hand Side Height = Distance between the 2 innermost holes
Width = Difference between the radius from the centre to the outermost hole, and the radius from the centre to the innermost hole
If it was ever possible to synchronise the disc accurately enough in the first place, minute inaccuracies in the shape and size of the filter would cause "purity errors" whereby even if the correct hue was obtained at the bottom of the picture it would be wrong at the top and vice versa. It may be a bit of a stretch to expect a striped filter to work with a Nipkow Disk, but they do work very well where the stability of the picture scan can be relied upon, i.e. LCD Pocket TVs, and LCD PC Monitors. Both of these use the same principle of a Black & White picture with stripes, viewed through a precision located colour stripe filter.

A Note on PAL:
It would be possible to synthesize a PAL signal through bmp to wav conversion, but it would be a very elaborate process. The key is to reverse the RGB sequence to become BGR on alternate scan lines. This is the "dot sequential" equivalent of PAL. It could be done by mirroring alternate lines of the bitmap in Paint Shop or Photoshop, then after converting to wav, carefully selecting the same alternate lines in Cool Edit and making them play backwards. It would not really be worthwhile for this kind of project, but it's nice to know that it could be done!