![]() I'll eventually be building a 'finished product' in a nice rackmount case.MEGATEXT used to be the most comprehensive of the teletext services, but it has been severely cut back over the past year. The only limitation is that you can't overwrite the 7th character on the first line, which is unfortunate. The keyboard is already there and everything! How about a status display for an embedded system? A few I2C commands aren't heavy on system resources! For example, I think it could make a very cool text editor. This PCB could be used as a 'video card' for an arduino, or anything that can control I2C. Perhaps there's interference getting into the IC and messing something up that way. Very possible,īut very hard to diagnose as my oscilloscope doesn't go up to 13 MHz so I can't really check it. Maybe the clock frequency is incorrect, whether because of a bad crystal or incorrect load capacitance. This seems unlikely to me however, as everything else that needs to decode it does so without a problem.īad Oscillator Frequency. It's perfectly possible that it's not getting a good signal, whether because of my inserter equipment or dodgy video leads. I can think of a few reasons why this may be.īad Teletext Signal. I'm getting some rather strange behaviour from the circuit from time to time, it often acts as if it's not getting a great signal and messes up the Other keyboard funtions include toggling line 24 on/off, magnifying the top/bottom half of the page and fastext links. If the page number is valid, it turns green and the search begins. Receiver, my decoder will not initiate a page search until the 'Enter' button is pressed. Each number appears as typed in red in the top left-hand corner. How mine works: Page numbers are entered via the numeric keypad. Unfortunately I know next to nothing about it, but here's Of my main goals was to imitate the old MRG systems decoder the BBC used for Pages from Ceefax. Technically it would be possible to use a USB keyboard but they require much more circuitry. My board is set up to be controlled by a PS/2 keyboard. Well as the cursor, should it be required. You can also toggle line 24 on/off for In Vision decoding, as Mainly because I can't be bothered, but also because Iĭon't think there were many services that didn't use P100 as their initial page anyway. Read the 'initial page' from packet 8/30, but I haven't written this yet. The current software sets the IC up asĪ master, outputting sync on pin 5 for the RGB converter. It took me a while to work out the software, but I've implemented a page calling function. Incidentally, the PCB is designed to connect to a seperate RGB to PAL converter, stay tuned to see how it works out! Software It often has to be adjusted for different devices, so it's very handy to have them on the The RGB output pots are very useful for adjusting colour. I should really have left the option to change some of the option pins, but as it is they are permanently set now! Also through-hole is WAY easier to work with. ![]() Say more? I could have used surface mount componets on this board, but there seemed little point as STV5348s in surface mount form are, as far as I can On the board, but I decided to just use an Arduino Nano for a variety of reasons, namely cost, time, ease of programming, space, availablity. Next, I could have put a micro controller IC I purposely have two video inputs on the PCB so that I have the choice of a BNC or RCA connector. I made a lot of mistakes on this PCB! The mounting holes aren't grounded properly, the resistors are too small and the keyboard socket is upside down! Strange issues so you might want to adjust this. I used 2 56pf caps for the Crystal, but I've no way of testing the frequency and get some I just used the 'Application Diagram' in the Datasheet. This circuit a few years ago for another project and used it again to convert the RGB signal to Composite video. Note that it outputs an RGB signal, so if you plan on using it with an old TV or something that doesn't support RGB you'll need Prototype Teletext In-Vision Decoder with STV5348 If you're looking for the final product, which is available to buy, see Here we have a teletext decoder built with and Arduino, STV5348 IC and a few other bits and pieces.įirst of all, why the STV5348? Well, it's cheap, easily available, doesn't require any RAM or other complimentaryĬhips and requires only a few external components.
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