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-   -   Homemade Teletext decoder (based on Mullard Module) (https://www.vintage-radio.net/forum/showthread.php?t=174220)

1980s_john 13th Dec 2020 5:26 pm

Homemade Teletext decoder (based on Mullard Module)
 
Hi,
Clearing out a cupboard I came across a Teletext decoder box I put together in the late 80s based on a Mullard VM 6101 module. The module has these 4 ICs:

SAA5020 Teletext Timing Chain Circuit
SAA5030 Teletext Video Processor
SAA5040A Teletext Control and Data
SAA5050 Teletext Character Generator

I gutted a push button telephone to make the keyboard, and it plugged the box into a Grundig portable 14" TV (long gone) which had a SCART socket plus a DIN socket for fast video blanking.

I'm sure I had the datasheet for the module but I can't find it, can anyone oblige please?

Thanks,
John

PS As to generating Teletext, I think last time I used a VCR with some suitable recordings off-air.

Philips210 13th Dec 2020 10:23 pm

Re: Homemade Teletext decoder (based on Mullard Module)
 
Hi.

I used to have the Mullard data on the VM6101 Teletext decoder but sadly it has long gone. There is some info in Television magazine. Have a look in the following issues:
Dec 1986, Jan 1987, Sep 1987 and Aug 1988. There is useful details on using the module in those articles. World Radio History has these issues available.

Regards,
Symon

1980s_john 13th Dec 2020 11:48 pm

Re: Homemade Teletext decoder (based on Mullard Module)
 
Thanks for heads up on the Television articles. I can't remember where I bought the module from but 15-20 seems right. Most of the design in the Television adapter is about the the keyboard interface. I used an EPROM to map from the 4x4 telephone keypad to the 7-bit code that the Mullard required as shown in the Dec 1986 article (I was limited to 14 different codes so picked what I thought were the most useful). As my TV had RGB + sync + blanking input there was no need for a UHF modulator. It really was a hack but it worked well.

Regards,
John

KeithsTV 14th Dec 2020 12:15 am

Re: Homemade Teletext decoder (based on Mullard Module)
 
There's a circuit for a teletext decoder using the Mullard ICs in the September 1980 Practical Electronics.
https://worldradiohistory.com/UK/Pra...0-09-S-OCR.pdf

I bought a surplus Mullard decoder in 1981 and using that circuit as a reference got it going. I also had the datasheets for the four ICs which allowed me to build a circuit to generate the control signals for it. I later wrote a program for my Acorn Atom to control it. It worked very well using a video output from my Thorn 1590 chassis TV and feeding the video output from the decoder into a monochrome monitor.

Keith

rambo1152 14th Dec 2020 1:16 am

Re: Homemade Teletext decoder (based on Mullard Module)
 
I had a Thorn 8000 in the kitchen that I added Teletext using the Mullard board.
I think I had to add a IR remote decoder on a bit of Varoboard


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