It just seemed unfair not to share this with you. I have no need for a scope as I already have a tek, but for those that don't have a scope, you might find this handy. The author supplies schematics, source code, and everything. Looks like you could build this in less than a day.
Well it's damn impressive, even down to using a tiny 8 pin PIC!
I might have to throw one together, just for a laugh.
If you want an LCD version, there's an example using a graphic LCD on Bill's Unicorn board - probably a higher spec than this version, but not as clever!.
It is pretty neat, I've not looked at the code is it NTSC or PAL?
Something to consider the 27MHz is outside the 12F675 spec, it may or maynot work with your 12F675
It is pretty neat, I've not looked at the code is it NTSC or PAL?
Something to consider the 27MHz is outside the 12F675 spec, it may or maynot work with your 12F675
More likely to be 27.something, not just 27MHz, for radio control. It's a value used in many TV sets, for either teletext/processor main clock or on the NICAM board (again for a processor clock). I might even have them in stock at work?, as it's a value which does tend to fail - I replaced one a few weeks back, for no teletext.
Well teletext will be discontinued over the next few years, it's part of the old analogue TV, and digital TV uses a completely different method.
I had to debug and connect to a TV one of the original Wireless World teletext decoder kits - it used all TTL chips (pre-CMOS), and had edge switches to select the text pages. It took a LOT of getting working, particularly as the only scope we had at work was an incredibly old antique, and it's spec was so low it wasn't true (it wasn't even triggered, it was synced).
But I got it all working, and fitted it in a Bush A823 based colour TV - we used it as a demonstration in the shop, the first teletext in the area (by a long way!).
The first actual teletext TV we saw was also a Bush, using a TIFAX module, and I actually had the set at home for a number of years, when it came back off rental. It predated IR remote controls, and was the most complex ultrasonic remote I've ever seen.
It said on the radio that the official opening was Friday (I think?), but while it was officially 'opened' it wasn't going to be useable until 6:00am the next morning - seems a strange 'opening' to me!
I've had a quick read of the article, the coil isn't to detune the crystal, it's to prevent the 3rd overtone crystal (most 27MHz are 3rd overtone) from oscillating at 9MHz instead of 27MHz.
I've just checked my crystals at work, and I used the last 27MHz one the other week but I've had a search around some teletext boards, and found one on a board. It's actually connected to a Philips SAA5246P teletext IC.
Looking at the circuit from the TV, there's a 4.7uH choke in series with the crystal, which is connected in a fairly strange way - presumably this is because it's an overtone crystal as well?.