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-   -   IMOGen Test Card & Teletext Generator (https://www.vintage-radio.net/forum/showthread.php?t=77624)

Parabola 16th Dec 2011 10:54 am

IMOGen Test Card & Teletext Generator
 
2 Attachment(s)
This is just a small update to last year’s threads, here and here, that detailed the early prototype development of a homebrew Test Card and Teletext Generator that I’d promised myself before the analogue switch off occurs here in London this coming April.

The stripboard prototype has now morphed into what you see in the attached images, and has gained the name "IMOGen" (Incrementing Memory Output Generator).

It can generate various colour or monochrome Test Cards, in differing line standards, and a selection of up to 6 Teletext pages with the current firmware. The VBI signals (Teletext and VITS) can be blanked where necessary for sets with frame blanking circuits never designed to deal with them. Input is 7-12v DC from a wall wart psu and output is 1vpp baseband video.

The front panel controls are –

1 x Rotary switch to select the required Test Card.
2 x Latching push buttons to respectively blank either Teletext or VITS or both.

The best way to think this unit’s capabilities is in terms of memory “slots”. These slots can be used for Test Cards as follows –

PAL Colour 625 = 4 Slots
NTSC Color 525 = 2 slots
Monochrome 405/525/625 = 1 Slot

As the unit has six slots, depending on the firmware loaded, any combination of the above that adds up to a total of 6 can be accommodated. Some possible examples would be –

1 x PAL625 + 1 x Mono625 + 1 x Mono405
or
3 x Mono 625 + 3 x Mono405
or
2 x NTSC525 + 2 x Mono525
etc, etc.

One page of Teletext is possible for every slot designated for storage of a 625 line Test Card. At present 16 reconstructed (re-coded from original screenshots) Teletext pages are available, but hopefully the library will grow as time allows.

Current sample units are loaded with 625 PAL Colour Test card F, Monochrome 625 Test Card C and 405 Test card D + 5 Teletext pages including the Engineering Test Page.

For those interested, the PCB was designed using the free “Design Spark” package from RS and was manufactured by the online PCBTrain service by Newbury Electronics.

I think that’s about it. If anybody is interested in further technical detail, screenshots or reconstructed Teletext pages, then I’ll post more as required :)

Mikey405 18th Dec 2011 4:22 pm

Re: IMOGen Test Card & Teletext Generator
 
That looks absolutely fantastic Parabola. I'll be your first customer when you put them on the market. :)

Kind regards.

From Mike.

dragonser 18th Dec 2011 6:41 pm

Re: IMOGen Test Card & Teletext Generator
 
Hi,
I hadn't see the earlier posts, but that looks like a nicely done project. please keep everyone updated. Am I right from reading the threads you mention that UV erasable eproms would not be fast enough to use ?
regards Peter

Parabola 18th Dec 2011 10:53 pm

Re: IMOGen Test Card & Teletext Generator
 
Thanks, both. Mike, the fiver we agreed is in the post :-D

Quote:

Originally Posted by dragonser (Post 489117)
.....UV erasable eproms would not be fast enough to use ?

The pixel rate is 12MHz so everything has to happen within 83ns. Finding fast enough UV EPROMs is both much harder, and considerably more expensive, than the 70ns FLASH PROMs I'm using. No reason why they couldn't be used if suitable parts were to turn up in a bargain job lot! It's always possible that 90ns UV EPROMs may work, though that's really hoping the spec is generous enough to just about allow it, being that nearly all the accessed addresses are sequential. I've never tried it.

The alternative would be to use slower UV EPROMs in Odd/Even address pairs to allow slower PROM access times, but the multiplexing and data latching requirements add complication, and one of my aims from the outset was to try to avoid having any further logic between the PROM data lines and the DAC. As certain people on here will know, mainly because I'm not smart enough to design it :-)

Tazman1966 19th Dec 2011 5:03 pm

Re: IMOGen Test Card & Teletext Generator
 
I already have one on trial and am very impressed indeed. I'll make my way over to you again sometime so that you may update the mono 625 card.

It's a must for keeping those teletext sets going :)

Now to source a system A VHF modulator for the 405 line card....

ppppenguin 19th Dec 2011 5:23 pm

Re: IMOGen Test Card & Teletext Generator
 
I have seen ImoGen and it's a well thought out design. What makes it special is its teletext support which it better than any previous testcard generator.

For VHF 405 use, there are several published designs for modulators.

Amraduk 19th Dec 2011 5:30 pm

Re: IMOGen Test Card & Teletext Generator
 
Hello Jeffrey,

Quote:

Originally Posted by ppppenguin (Post 489329)
What makes it special is its teletext support which it better than any previous testcard generator.

Although both are no longer available, Richard Russell and Dave Grant's testcard generators also supported teletext!

Regards,

Dave.

ppppenguin 19th Dec 2011 5:44 pm

Re: IMOGen Test Card & Teletext Generator
 
Dave, I'm well aware that both Dinosaur and RTR generators had some teletext capability. ImoGen has more extensive teletext support. Exactly how much I'm not sure.

Parabola 19th Dec 2011 6:57 pm

Re: IMOGen Test Card & Teletext Generator
 
Thanks Tas and Jeffrey, more fivers to post. That's the entire marketing budget spent now. I knew I should've allowed at least £20, but I spent it all on PROMs :D

Tas, I still haven't fixed the high frequency grating in the 625 TCC source image, but the version I have now is nicer than what you currently have in that slot. I can always post you a PROM so as to avoid the Christmas traffic.

Quote:

Originally Posted by Amraduk (Post 489331)
.....
Quote:

Originally Posted by ppppenguin (Post 489329)
What makes it special is its teletext support which it better than any previous testcard generator.

Although both are no longer available, Richard Russell and Dave Grant's testcard generators also supported teletext!

As far as I'm concerned, although I've never owned one or even held one, Richard Russell's generator is the gold standard in this class of device and nearly everything I have done is to try to go some way to emulating what is possible with his design. I'm getting there, but IMOGen still needs a "next generation" to become easily user programmable, and I've not even attempted to add some of the extra features that his unit can offer but are not of so much interest to the vintage tv user (widescreen signalling and fast text, for instance).

I think that Jeffrey was being kind to me here by promoting the fact that, in it's current form, IMOGen can store up to six text pages. This is more than the four that RTR's generator stores at one time. This is related to the available PROM space and the number of complete frames stored. The other feature that I incorporated is the front panel selectability of the VBI signals. This allows the instant blanking of the Teletext data lines and VITS if required. Of course, you can choose whether to program them, or not, with RTR's generator, but that does involve a trip to a PC to achieve the same result.

As far as I know, and I know very little about what was offered with Dave Grant's Dinosaur TCGen, it only produces one page of text which contains some design details and credits about the generator itself. I'd be interested to hear differently because it should certainly be able to do at least four if correctly coded to. I don't believe the VBI signals would be blankable without reprogramming the PROMs.

Also what Jeffrey may be thinking of is my intention to try to double the available text pages with a new version of firmware in future. This will involve some address swapping manouvures during the relevant data lines and should be possible as long as I don't run out of macrocells in the CPLD to implement the logic. There is plenty of space in the PROMs. I need to get my VHDL head on (watch out!) to look at this seriously in the near future.

As you say, the main problem with the two excellent designs that you mentioned is that, nowadays, you cannot buy them anymore. Hence my efforts with IMOGen, mainly to satisfy my own need.

Jeffrey has also been kind by not mentioning that our recent comparative tests showed that the reconstruction filter in IMOGen is not quite as good as the Dinosaur design. This isn't all that surprising, because the Dinosaur filter is more complex and looks like it's been designed by someone who knew what they were doing, whereas mine is relatively simple and was designed by some freeware analogue filter software. This is the most tricky and infuriating element of the design, as trying to make a half decent reconstruction filter, I've learnt, at a sample rate as low as 12MHz is always going to be a series of compromises. I'm still working to improve this at the moment, even though the differences we are talking about can only really be discerened on a professional monitor and are, mostly, not an issue with real world vintage TVs.

ppppenguin 19th Dec 2011 7:30 pm

Re: IMOGen Test Card & Teletext Generator
 
If we were looking at a wish list for an ideal design it would include any or all of:
  • SRAM or DRAM to hold the current image or even an image sequence
  • Flash memory interface (USB or SD card) to hold lots of images
  • USB interface for PC control, perhaps even for dynamic teletext
  • Higher sample rate (13.5MHz), with oversampling probably computed at picture load time, to solve output filter problems
As it is, ImoGen fills a gap in the market and does it well.

Amraduk 19th Dec 2011 9:19 pm

Re: IMOGen Test Card & Teletext Generator
 
Hello Jeffrey

Quote:

Originally Posted by ppppenguin (Post 489336)
Dave, I'm well aware that both Dinosaur and RTR generators had some teletext capability. ImoGen has more extensive teletext support. Exactly how much I'm not sure.

Fair enough, though the impression I got from what you wrote, was that you weren't aware of their teletext capability!

Regards,

Dave.

Amraduk 19th Dec 2011 10:09 pm

Re: IMOGen Test Card & Teletext Generator
 
Hello Parabola,

Quote:

Originally Posted by Parabola (Post 489356)

I think that Jeffrey was being kind to me here by promoting the fact that, in it's current form, IMOGen can store up to six text pages. This is more than the four that RTR's generator stores at one time. This is related to the available PROM space and the number of complete frames stored.

As far as I know, and I know very little about what was offered with Dave Grant's Dinosaur TCGen, it only produces one page of text which contains some design details and credits about the generator itself. I'd be interested to hear differently because it should certainly be able to do at least four if correctly coded to.

In the version of Dave Grant's TC Generator that I have, images are stored in pairs of EPROMs, one pair can store one colour or four monochrome images, a total of four frames. It is, therefore, possible to have four teletext pages per EPROM pair, which represents four pages for a colour image and one teletext page per monochrome image per EPROM pair.

There was no easy way to produce images for Dave's generator before Richard Russell produced his TC Generator. The programming software it uses can also be used to produce files that can, with some manipulation of the data locations, be programmed into a pair of EPROMs that will work in Dave's generator!

As for the reconstruction filter, I was told (I forget by whom) that the one in Richard's generator is better than the one in Dave's generator!

Regards,

Dave.

Parabola 19th Dec 2011 10:32 pm

Re: IMOGen Test Card & Teletext Generator
 
Thanks, Dave.

That's pretty much my understanding. The fields are stored as 8 x 256K gapped EPROM images within two larger 8MB EPROMs, so 4 frames per PROM pair.

I accept that you can reprogram Dinosaur if you have the means to manipulate the data how it's required. What I don't know, and it's only a point of passing interest, is if Dinosaur ever came pre-programmed with a selection of Teletext pages.

I would be very surprised if RTR's reconstruction filter wasn't the best - without doubt the man certainly knew what he was doing.

Quote:

Originally Posted by ppppenguin (Post 489377)
  • SRAM or DRAM to hold the current image or even an image sequence
  • Flash memory interface (USB or SD card) to hold lots of images
  • USB interface for PC control, perhaps even for dynamic teletext
  • Higher sample rate (13.5MHz), with oversampling probably computed at picture load time, to solve output filter problems

No to number 2, but it's more than possible that the next version will be a USB device containing an SRAM frame buffer and a DAC - all else done in software. That would allow for all the other "wishes", and I'm starting to enjoy writing software more than straining my eyes with soldering SMDs!

dragonser 19th Dec 2011 10:38 pm

Re: IMOGen Test Card & Teletext Generator
 
Hi Parabola, many thanks for the reply,
I only asked about the uv eproms as I have some second hand 27c4001 eproms here.
again the project looks most impressive,
sorry for asking another question, but how easy would it be to add in another TV standard ? Of course having the 625, 525 and 405 options should cover most requirements ( certainly in the UK ).
regards Peter

Amraduk 19th Dec 2011 10:55 pm

Re: IMOGen Test Card & Teletext Generator
 
Hello Parabola,

Quote:

Originally Posted by Parabola (Post 489440)
Thanks, Dave.

You're welcome.

Quote:

I accept that you can reprogram Dinosaur if you have the means to manipulate the data how it's required.
Indeed. I am working on some software to 'automate' the process, using another of Richard's products, his BB4W - BBC Basic For(4) Windows.

Quote:

What I don't know, and it's only a point of passing interest, is if Dinosaur ever came pre-programmed with a selection of Teletext pages.
I don't believe so, based on what Dave said about getting them programmed! I think they only ever came with the teletext page(s) you mentioned, certainly, that was all that was present when I got mine.

Regards,

Dave.

Parabola 20th Dec 2011 12:39 pm

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by dragonser (Post 489442)
....how easy would it be to add in another TV standard ? Of course having the 625, 525 and 405 options should cover most requirements ( certainly in the UK ).

Assuming it's not beyond the mathematical restraints of the coding regime, then producing differing standards is the function of the various rag-bag collection of software apps that I've written, or hacked, and use to create suitable PROM images for my hardware (all written in BB4W, Dave ;) )

What is the standard you have in mind?

Amraduk 20th Dec 2011 1:11 pm

Re: IMOGen Test Card & Teletext Generator
 
:)....

Parabola 20th Dec 2011 6:30 pm

Re: IMOGen Test Card & Teletext Generator
 
As mentioned previously, I've re-coded a selection of original Teletext pages for use with IMOGen - currently 16 in all.

There is also a small, self-contained Windows viewer application that allows them to be viewed on a PC for selection purposes prior to programming.

If anyone would like to take a trip down the Teletext memory lane themselves, then this application can be download from here -

http://www.vintagepixels.co.uk/imoge...View_v1-07.zip

Just extract the two files contained in the zip file to a new folder - double click on the executable to run it, then load Demo.car from the "File" menu. The upper menu bar navigation options will then become active and are fairly self-explanatory.

Hope you enjoy the nostalgia!

PS: For those who already have an earlier copy, this version (1.07) has correct implementation of double height control code emulation and so displays the Engineering Test Page correctly. It's probably worth replacing your previous version :)

pichacker 21st Dec 2011 8:57 am

Re: IMOGen Test Card & Teletext Generator
 
Hi,

I downloaded the zip and Symantec said it would not allow it because it was infected with "bloodhound.sonar.9" whatever that was....

Otherwise very impressed with youe construction work....Professional.

Regards

Steve.

ppppenguin 21st Dec 2011 9:00 am

Re: IMOGen Test Card & Teletext Generator
 
When Parabola demo'ed his software to me he said ignore any warnings. Apparently he hasn't put in some bit of code that certifies it as a genuine window prog. I don't claim any understanding of this but I know him well enough to say that he's not going to be distributing malware.

pichacker 21st Dec 2011 9:11 am

Re: IMOGen Test Card & Teletext Generator
 
Jeff,

I did actually get the prog up and running, just before symantic shut it for me, and it did indeed look good. I'm guessing that there is a signature in the code that symantic is being over zelous with and mistaking it for something that it may not be.

Keep up the good work...

Steve.

Parabola 21st Dec 2011 9:26 am

Re: IMOGen Test Card & Teletext Generator
 
What Jeffrey is referring to is that the earlier versions didn't contain the Microsoft version info resource (the fields you see when you view the properties of an executable through right clicking on it) whose absence tends to upset some virus scanners (Avast, for one). However, I have now added the resource in v1.07.

I've never had a threat warning reported for this app before, other than because of the anomoly mentioned above. I have downloaded the version posted online, verified it hasn't been modified from my master and have run it through two anti virus scanners, AVG and Avast, which both report no threat found.

I would suggest that you are receiving a false positive based on Symantec's heuristic analysis of the file contents. It's written in BBC Basic for Windows and this is not an unknown occurrance with BB4W apps and some aniti virus programs.

Of course, the ultimate decision is always going to be yours :)

dragonser 8th Jan 2012 11:53 am

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Parabola (Post 489582)
Assuming it's not beyond the mathematical restraints of the coding regime, then producing differing standards is the function of the various rag-bag collection of software apps that I've written, or hacked, and use to create suitable PROM images for my hardware (all written in BB4W, Dave)

What is the standard you have in mind?

Hi,
many thanks for the explanation, it helps to know
that the changes could be implemented if there was sufficient demand.
One standard that I have seen mentioned here is 405 line NTSC but I know that that is probably quite an obscure one.
regards Peter

Parabola 10th Jan 2012 11:18 pm

Re: IMOGen Test Card & Teletext Generator
 
405 is an interesting standard to generate at 12MHz, but that's probably a different thread altogether :-/

405 Line NTSC is certainly possible.

I've just completed, though so far not tested, a new version of firmware (VHDL) that, along with a revised PROM layout, allows a total of 18 (yes, 18!) Teletext pages to be produced by the same hardware, without losing any of the previous functionality. This has taken many attempts and incarnations of the code, as it really didn't want to fit into the available 64 macrocells! Fingers crossed it works out....

Tazman1966 11th Jan 2012 7:59 pm

Re: IMOGen Test Card & Teletext Generator
 
I look forward to getting together and seeing the results :)

Parabola 12th Jan 2012 10:19 pm

Re: IMOGen Test Card & Teletext Generator
 
Hello Tas,

Well it's looking promising. Firmware version 2.3MT (MT = MaxText) has passed the first real word operational test.

I manually created a 'new format' single frame 625 mono PROM, including 3 text pages, and installed it into one of the spare production units. Then updated that unit to the latest firmware. On hooking it up to a TV the Test Card image was generated fine, and all 3 text pages could be selected...so looking good :)

I now need to create an 8 field / 4 PROM PAL colour set, including 12 text pages (3 per PROM) and test that to ensure that the subcarrier phasing is maintained throughout all the addressing manouvres. Should be fine, I think :-/

Then I need to re-write the PROM creation app so it builds PROM images in the new format.

When I've got it sorted I'll give you a shout and we can upgrade your unit. It now seems a little futile to have asked you to select four pages from the available catalogue, when now you can have all of them!

Parabola 13th Jan 2012 7:11 pm

Re: IMOGen Test Card & Teletext Generator
 
There has been some mention previously in this thread, and in some others in the past, in fact it appears to be a popular misconception, that Richard Russell’s Test Card Generator is no longer available to buy. I have been in touch with Richard today and he assures me that this is not the case.

The Turkish company linked to on Richard’s page here are still willing and able to supply units to the UK. I know at the moment the linked webpage seems to be just a blank white page, and it has been reported previously, here as one example, that they don’t always respond to emails. Therefore it may be worthwhile contacting Richard directly if you do want one and experience any communication problems.

All of which kind of makes the rationale for developing IMOGen any further, or indeed at all in the first place, rather questionable and I shall put an end to my witterings about it at this point.

Mods: Now may be a good time to close this thread as I think as it’s pretty much run it’s course. Thanks.

Andy Green 13th Jan 2012 8:36 pm

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Parabola (Post 495724)
... All of which kind of makes the rationale for developing IMOGen any further, or indeed at all in the first place, rather questionable and I shall put an end to my witterings about it at this point.

I wouldn't agree. It's always fascinating to see this sort of development work described on the forum.

I have an RT Russell test card gen, for many years now, and it is a great piece of kit, but it is a few years old now. (I also have to Auroras, the 1st Gen multi standard and a later single standard model)

The ability to hold 16 pages of text is a great improvement, and I for one would be interested in one for this reason alone.

Alos as RS232 serial ports become scarcer, a USB interface (or even an IP) would be very beneficial!

How about publishing the board layout, providing the eprom images and
allowing others to build thir own units, if you don't want the trouble and expense of selling completed units or kits?

Certainly you shouldn't consider your work as a waste of time in any way!

Andy EI3HG

Parabola 13th Jan 2012 10:43 pm

Re: IMOGen Test Card & Teletext Generator
 
I don't think any of it is/was a waste of time. I just thought it best this thread faded away asap, as it contains certain incorrect statements about the non-availablility of Richard Russell's generator.

terrykc 31st Jan 2012 4:35 pm

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Parabola (Post 489651)
As mentioned previously, I've re-coded a selection of original Teletext pages for use with IMOGen - currently 16 in all.

There is also a small, self-contained Windows viewer application that allows them to be viewed on a PC for selection purposes prior to programming.

If anyone would like to take a trip down the Teletext memory lane themselves, then this application can be download from here -

http://www.vintagepixels.co.uk/imoge...View_v1-07.zip

Just extract the two files contained in the zip file to a new folder - double click on the executable to run it, then load Demo.car from the "File" menu. The upper menu bar navigation options will then become active and are fairly self-explanatory.

Hope you enjoy the nostalgia!

I would like to enjoy the nostalgia!

Unfortunately, the files are no longer available.

Any chance of making them available again?

terrykc 1st Feb 2012 10:47 am

Re: IMOGen Test Card & Teletext Generator
 
This talk of Teletext test pages brings back memories of designing test pages for the Stock Exchange TOPIC (Teletext Output Price Information Computer) system over 30 years ago!

The only editing terminal available on the development system was intended for use on the BT Viewdata system and only handled (and displayed!) the features of the original system, so I used my crib sheet of escape sequences to enter 'new' facilities like double height and background colour - and hoped that when I saw the result on my prototype decoder that all would be well!

My repertoire included a crosshatch and pages for checking/setting purity, etc., so that the maintenance staff didn't need to cart test equipment around the streets of the City of London ...

Parabola 5th Mar 2012 12:25 pm

Re: IMOGen Test Card & Teletext Generator
 
4 Attachment(s)
Hello again,

As this thread is still open, and the final development work mentioned in post #26 is now complete, I thought I would just add a final update to conclude the story.

Just to recap. The new firmware and PROM layout allows 3 pages of text per frame (PROM). So, for an 8 field (4 frame) 4 PROM PAL colour test card 12 pages of text are possible, and for a 2 field (single frame) 1 PROM monochrome test card 3 pages are possible. This means that for a unit configured with all 625 test cards the total text pages held can be a maximum of 18. If the unit is configured to include a 405 test card, and thus only two 625 test cards, the maximum available text pages drops to 15.

The total available pages are divided up into separate magazines. The 12 pages available when the colour test card is selected are in the 1xx (100,101,102 etc) range, with the remaining two mono test card selections having pages in the 2xx and 3xx ranges respectively. This is necessary to avoid confusion to the poor old teletext decoder when switching between test card selections. If this is not done, then the situation can arise that if you manage to switch between test cards (and thus text magazines) between fields within a frame, it is possible to end up with the top half of one page and the bottom half of another – most disconcerting! A well defined numbering system prevents this.

As it’s time to wrap this saga up, I really should publicly thank a few people (Oscar-esque speech coming!)

Firstly, to Richard Russell, whose own TCGEN was a huge inspiration for this project, and whose BB4Win made is possible for a numpty like me to be able to create software applications powerful enough to create and manipulate PROM data how I needed it.

Secondly, to Jeffrey Borinsky, for finally pushing me down the CPLD route, and away from CMOS/TTL – it was key to this design getting to the point it has. Also, for his patience dealing with my daft questions whilst trying to get to grips with VHDL, digital PAL coding, and the black art of DAC reconstruction filters.

Finally, to my beta testers and fellow TV hoarders, you know who you are, who have provided feedback, support and encouragement through the darker times when it all seemed to be too much effort.

Thank you, all ;)

So, to finish up, a whole sequence of pictures (if I get them all uploaded) showing an all 625 configured unit doing it's stuff through a 26” 1979 Philips G11 with Teletext and Viewdata decoders, touch tuning and ultrasonic remote.

All moiré patterns and strange colour rendition (orange reds!) are down to the camera, sorry.

The first set of pictures show –

1) The set-up – IMOGen --> Modulator --> G11
2) 625 PAL Colour Test card, TCF
3) 625 Mono Test Card 1, TCC (625 version)
4) 625 Mono Test Card 2, TCD (not accurate for 625, but for input to an Aurora)

More to follow…..

Parabola 5th Mar 2012 12:26 pm

Re: IMOGen Test Card & Teletext Generator
 
5 Attachment(s)
Teletext Pages 100 - 104

Parabola 5th Mar 2012 12:27 pm

Re: IMOGen Test Card & Teletext Generator
 
5 Attachment(s)
Teletext Pages 105-109

Parabola 5th Mar 2012 12:29 pm

Re: IMOGen Test Card & Teletext Generator
 
5 Attachment(s)
Teletext Pages 110 - 111 and 200 - 202

Parabola 5th Mar 2012 12:30 pm

Re: IMOGen Test Card & Teletext Generator
 
3 Attachment(s)
And finally, Teletext Pages 300 - 302

That's all folks :-)

Brian R Pateman 5th Mar 2012 12:35 pm

Re: IMOGen Test Card & Teletext Generator
 
Excellent results!

It's nice to see them displayed on a top class television too.

(Now you see why we don't routinely close threads at the OP's request).

terrykc 5th Mar 2012 1:34 pm

Re: IMOGen Test Card & Teletext Generator
 
Absolutely fantastic!

One observation - I would have preferred a more optimistic weather forecast ...

This reminds me of a Philips pattern generator we had in the late 80s which generated a teletext test page using only one line per field!

I can't remember anything about the test page - except that I thought it was rubbish! So, I took the test page from our Viewdata system, modified it slightly, and replaced the PROM image in the generator.

I recalled a bit of the Broadcast Teletext Specification which, as far as I know, anybody has ever used, which says that rows can be transmitted in any order.

As rows 11 and 12 of my page contained ENGINEERING TEST PAGE in double height, I started with that, followed by rows 13, 10,14,9,15,8 etc.

With the page spread over 24 frames, the appearance was reminiscent of a faster version of the well known Thames TV ident ...

Tazman1966 5th Mar 2012 8:06 pm

Re: IMOGen Test Card & Teletext Generator
 
An excellent piece of kit that I can vouch for having one of the first :)
I look forward to the update when I can get myself and the unit round to your place.

Thanks again.

Parabola 5th Mar 2012 11:26 pm

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Brian R Pateman (Post 510196)
It's nice to see them displayed on a top class television too.

Yes, it is certainly a very grand set and the sole reason I needed a Teletext Generator at all, as it's the only vintage Teletext set I have. A Viewdata generator (probably just as a software app) with connection via modem is is the next task.

Quote:

Originally Posted by terrykc (Post 510224)
Absolutely fantastic!

One observation - I would have preferred a more optimistic weather forecast ...

Thanks. Sorry about the weather outlook. It took me about 6 hours to re-code that page back into 7 bit ascii from a .gif of the original and, to be honest, the actual forecast wasn't the highest priority in my mind ;)

Quote:

Originally Posted by terrykc (Post 510224)
This reminds me of a Philips pattern generator we had in the late 80s which generated a teletext test page using only one line per field!...

IMOGen puts out 12 lines per field, so the page counter between page selections moves like a blur! I was a little concerned at first as to whether so many lines would be tolerated by such an early decoder as is in the G11, but it deals with it without issue.

IMOGen now uses 6 separate switchable VBIs per frame/PROM, which is 72 stored data lines. These separate VBIs are 'paged' in and out in a sequence controlled by the CPLD. Sequencing VBIs within individal PROMs and across multiple PROM sets was quite a challenge with a mere 64 macrocell CPLD - I ended up using 63 of the available macrocells in the end, although it was the whole 64 in one version. Creating the PROM images to maintain correct page numbering and subcarrier/burst phase throughout all this sequencing and paging also took some work.

Quote:

Originally Posted by terrykc (Post 510224)
I recalled a bit of the Broadcast Teletext Specification which, as far as I know, anybody has ever used, which says that rows can be transmitted in any order.

Well yes, as long as you keep a track of where your header rows are inserted. One out of sequence data line on the wrong side of a header row and it all goes to pot!

Quote:

Originally Posted by Tazman1966 (Post 510354)
I look forward to the update when I can get myself and the unit round to your place.

Yep, I'll sort that out asap. I've got some new, different, buttons on order too :)

terrykc 6th Mar 2012 10:48 am

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Parabola (Post 510429)
... Sorry about the weather outlook. It took me about 6 hours to re-code that page back into 7 bit ascii from a .gif of the original and, to be honest, the actual forecast wasn't the highest priority in my mind ;) ...

It's quite a coincidence that the forecast you 'brought back from the dead' bears a marked similarity to the weather we've been experiencing over the last few days!

Quote:

Originally Posted by Parabola (Post 510429)
IMOGen puts out 12 lines per field, so the page counter between page selections moves like a blur! I was a little concerned at first as to whether so many lines would be tolerated by such an early decoder as is in the G11 ...

All versions of the UK Teletext Specification (there were three) specified that all 16 available lines in the VBI could be used. Although the early TIfax decoder was designed before the 'new' features (background colour, double height, etc.) were added, it worked on all 16 lines.

I know what you mean about the page numbers - we used 14 lines for the test pages and bridged BBC1 CEEFAX onto the remaining two.

CEEFAX was used to create interest and demonstrate the capabilities of Teletext but, in reality, the primary purpose was to test the capability of a large, private, cable TV system by means of an error counter piggy-backed onto the TIfax decoder.

Quote:

Originally Posted by Parabola (Post 510429)
Quote:

Originally Posted by terrykc (Post 510224)
... rows can be transmitted in any order.

Well yes, as long as you keep a track of where your header rows are inserted. One out of sequence data line on the wrong side of a header row and it all goes to pot!

Agreed, but it wasn't a problem with the Philips generator as the row numbers were included in the data. It was simply a case of re-ordering the data before burning the PROM.

Andy Green 6th Mar 2012 10:31 pm

Re: IMOGen Test Card & Teletext Generator
 
Excellent work Parabola! (I want one!)
This thread has reminded me to root out a S-VHS tape and record the Irish analogue stations teletext before ASO in August this year

Parabola 7th Mar 2012 11:08 pm

Re: IMOGen Test Card & Teletext Generator
 
Thanks, Andy.

Well, it's possible that there may be a spare from the initial build of 10 units, once everything shakes out. If so I'll let you know. I would possibly build more if there were to be any demand, but the PCB already needs redesigning due to one component becoming obsolete in through hole form.

Paul Stenning 8th Mar 2012 3:48 pm

Re: IMOGen Test Card & Teletext Generator
 
You can get SMT to through-hole adaptors for some IC packages. That may be an easier/cheaper option than redesigning the PCB.

Parabola 9th Mar 2012 9:37 am

Re: IMOGen Test Card & Teletext Generator
 
Thanks, Paul. Yes, that's certainly another option.

Tazman1966 2nd Nov 2012 2:06 pm

Re: IMOGen Test Card & Teletext Generator
 
Quote:

Originally Posted by Andy Green (Post 510718)
Excellent work Parabola! (I want one!)

Well you can now!

http://www.pges.co.uk/imogen/index.html

I was contacted about using my photos of my Korting showing test cards from the IMOGen and of course I said yes and they're here on his website along with plenty of information about the test card generator.

Cheers,

Tas:thumbsup:

chriswood1900 23rd Nov 2012 3:11 pm

Re: IMOGen Test Card & Teletext Generator
 
I have just taken delivery of my Imogen from Graham, very impressed and seems a bargain to me. Very useful alongside an Aurora and great fun being able to get Text back on my colour TVs. For more info have a look at the website in the link above.
A happy customer Chris

petertheorgan 23rd Nov 2012 10:21 pm

Re: IMOGen Test Card & Teletext Generator
 
4 Attachment(s)
I have also just taken delivery of my Imogen from Graham and it is a super piece of kit ! which I can well recommend ,

I have attached a few photos but they do not do it justice, perhaps it means that some full 625 restorations are in order now that I have been dragged screaming into 1967 !

another very happy customer

peter

winston_1 24th Nov 2012 12:30 am

Re: IMOGen Test Card & Teletext Generator
 
I took delivery of one last week as well. I'm delighted with it as well.


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