Transferring data with your TV

Last week’s article focused on the universal Basic, called BASICODE and how radio was used to transfer the data as “sounds” to the computer.
This “hard-bit-rock” as it was called by the German TV Show: “WDR Computerclub” was also transmitted over the TV, but it remained basically the transfer of the sounds, the bleeps and bops, that you had to record on a cassette.  It meant that albeit the medium was now your television, it was essentially still transmitting data as sounds.

Then in 1985 Michael Wiegand came up with a clever little idea: why not use part of the screen as a “data block”, in which you could alternate black and white strips, the zeros and ones basically and have some little device (consisting of amongst others a UART), placed between the TV or video recorder and the serial port of your computer, convert the data or bits and have a program on the computer read it out.

Basically, the video signal would be read with the white stripes coming in at 0,93 Volt representing a binary “0” and the black stripes at 0,3 Volt representing a binary “1”. The UART would then convert these voltages to the RS-232 standards of 0 Volt and 5 Volt, representing the Binary “0” and “1” respectively.
Using this technique, they were able to transmit 50 bytes of data per second, whilst still have the regular TV show on screen in parallel. This resulted in roughly 90K of data per show of 30 minutes.

When you watched the show, you could actually see this little “data block” in the top left corner of the screen.

The following years they perfected this concept by extending the data block to the full width of the TV screen and enhance the decoder. This made them reach data transfer speeds of 200 – 1280 bytes per second, which allowed them to transmit bigger and more complex programs that made use of graphics as in BASICODE v3C.

The concept of “data via TV” became then a commercialized service in Germany in the early 90s when the Videodat signal was broadcast as a paid service called “Channel Videodat” over the TV provider ProSieben for which you had to use their proprietary decoder.

For many it remained a good and fast alternative for the regular modem and telephone data transfer as the relative high-speed data transfer via ISDN was quite a costly affair. The service remained in operation till 1995 when Channel Videodat filed for bankruptcy as the internet was becoming more and more popular and effectively replaced the Videodat “mini-internet”.

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