A bit of history …
More than two decades ago, I needed to generate a second video-output on a computer platform that didn’t support the notion of multiple graphics cards. This second output didn’t have to be high-resolution … in fact, low-res was desirable. It needed to show simple text in composite video, as a teleprompter.
I hit upon an expansion card that was actually built to decode Teletext data from TV broadcasts. This card had an analogue TV tuner and a Philips Teletext decoder IC. It could also output those decoded pages to a separate monitor. By sending it the right commands, it was possible to disable the teletext-acquisition circuitry, and instead poke data into its RAM directly … effectively turning it into a sort-of “teletext quality” graphics card.
When the project eventually retired, the computer and teletext card were disposed of. After-all: no-one needs Teletext decoders now that all those services are switched off, do they?
What a mistake that was! I have done so many projects since which would have been better with a simple, clear monitor display! It was a great device, requiring minimal code to control. It would have been perfect for lots of homemade-computers, home-automation displays, and more. You just needed a 15 kHz monitor, or old TV with RGB input.
And now …
Fast-forward from the mid-nineties to now, and a chance conversation online in a Teletext discussion group (because for many of us, Teletext is still A Thing) reminded me of all this. Some investigations, some searching around old TV-spares websites online, some purchases, some PCB design …
And here it is! Containing only the functionality I needed from that original expansion card, and about a quarter of the size.
I call it my Teletext Experimenter’s board. It:
- decodes teletext data from a composite-video signal
- displays the currently-loaded page as 15kHz RGB
- supports the standard teletext functionality (the colour buttons, zoom, reveal, hold, etc)
- displays whatever teletext data you send it – use it as a Teletext-quality display in your own projects!
It is powered by standard 5v and controlled with I2C, making it compatible with a wide-range of micrcontrollers and computers (so far I’ve used it successfully with an Arduino, Raspberry Pi, and one or two Acorn computers). It has header pins for 5v supply, I2C control, composite-video input (for teletext decoding) and RGB output. I’ve also added a phono socket (for the composite video input) and a 9-way D-sub connector (for RGB) as alternative connectors that are a bit more sturdy than header pins.
I hope that this project will be of interest to electronics hobbyists, Teletext enthusiasts (possibly who would like something to decode their vbit2 streams) and Teletext artists who’d like to see their work on “real” hardware. I can think of a few of my own projects which might benefit, but I’d really like to see what other people do with it too!
I really can’t stress this enough: this project requires you to be comfortable with amateur digital electronics, and know how to work with I2C. It won’t do anything on its own – it needs some sort of controller to tell it what to do. That controller could be an Arduino, a Raspberry Pi, a PIC microcontroller, a Propellor, an Acorn Archimedes, a BBC Micro … or indeed, any controller than can control devices with I2C.
I intend to blog it all here, as usual, along with lots of implementation examples for different platforms. I’ll be providing enough information so you can build your own if you want, but I also hope to sell some kits on Tindie. Please seriously consider helping out a poor, amateur geek by buying a kit – I have development costs it would be nice to recoup, and any extra money I make just goes back into funding more development.
Kits should appear on Tindie just as soon as I’ve written-up enough documentation and sorted my stock. In the meantime: if you’d like to be an early-adopter, and are willing to accept some potential teething troubles and poor documentation in exchange for a lower kit price, then please get in contact and I’ll sell you one early. (The introductory price is 50 UKP. Postage free to the UK.)
I’m particularly looking for people who are confident in their electronics, who could spot how I could make the circuit better. There are a few minor changes I’m going to make to the next PCB design, but feedback from other people would be smashing too!
E-mail me at: