Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Wow! I'd forgotten I did that stuff, less than four years ago, senility, it creeps up on you!!
Somewhat surprised you're able to get it work at other rates than those I envisaged...that's seemingly without modifications, no doubt about your abilities!
Failures, well, using re-cycled components as you often do, that's bound to happen, but I'm pleased to see someone doing it! I'm guilty of not doing so.
I'm at a bit 'stuck' at the moment. I have the SSTV-TV/VGA thing to do, maybe an updated 'ROM-scanner' and a blend of the 'ROM-scanner' and a CRT display in a single unit. Maybe. Decisions, decisions...(Later) Oh! and the NBTV PC-based DC-coupled record/playback device...that's in addition to 'real work' and my other passion - flying! Perhaps at this point I should also mention the wife...
Steve A.
Coming back on-topic, it'll be the SSTV-TV/VGA thingy first, the DC-coupled recorder second, then (perhaps) the updated 'ROM-scanner', with or without the display...but I'm open to other suggestions...
The updated 'Rom-scanner' is a concept, stores 1024 images in the same format as Ralph's (8k-byte each), maybe four/five DIL/SOIC/SOIJ chips, one 28-pin DIP/DIL device (the micro), the others smaller, nothing exotic...
Harry Dalek wrote:Well that sounds good too! I think more than 2 would be hard to juggle
Steve Anderson wrote:Yep. Now (I think) I'm around the 'blockage' [1] I had with the SSTV up-converter the others will fall into place in time. I do feel duty-bound to complete the SSTV-TV/VGA first though. The others, well, we'll see...they are somewhat embryonic at this stage...though an interesting distraction over the past while...sometimes you hit an impasse, "How in the heck am I going to do this?" I hope I've found it! It's as if the brain's digestive system works on it, in my case often while I'm asleep, a 'Eureka' moment..though not to be said in the same breath as Archimedes or Einstein...
Interesting to note both those gents surnames start with a vowel, so does mine, nah!, forget it Steve...
Steve A.
[1] Maybe constipation would have been a better word?
Steve Anderson wrote:Well I'm surprised they continue to operate well away from the frequencies they were designed for, I must have had a good day that day! I don't recall as it was five years ago as noted on the circuits.
I would guess the bandwidth limitation will be set by the opto-coupler arrangement, mainly on the output (CRT) side and to a lesser extent the op-amps used. Overall a bandwidth of 30-50kHz is probably the limit, perhaps a bit less. I think I checked it to around 15kHz but didn't go any further.
Steve A.
Harry Dalek wrote:OH the Opto coupler bandwidth is lower than expected , i think it would be higher than 15khz since 64 line looks ok more than likely using all the pcs audio bandwidth ,i suppose there might be better opto couplers for this. Any case interesting
Steve Anderson wrote:
Opto-couplers can be improved in bandwidth to an extent, but the simple circuit in the CRT application above does impose some limits. A short (glass)fibre-link is one answer, but the optical components for high-speed aren't as cheap as an opto-coupler and generally logic devices, not linear, requiring an A-D and a D-A plus all the support stuff.
A short RF link (a few cm) is another option, a few micro-watts is enough, but interference could be a problem, and more complexity added.
Those are what spring to mind at the moment, there are surely others...
The dual (one LED, two photodiodes) opto-coupled device in the attached datasheet (IL300) claims a bandwidth to 200kHz and excellent linearity. (Implying a rise/fall time of 1.75us). Worth considering. But the CRT grid-drive arrangement mentioned above would also need an overhaul.
There are other very similar devices that go up to 1MHz or more...
Harry Dalek wrote:Yes 200khz is a big improvement not really a drop in replacement but interesting for sure
Steve Anderson wrote:Harry Dalek wrote:Yes 200khz is a big improvement not really a drop in replacement but interesting for sure
Yes, but they're smaller and not prone to external magnetic fields or a transformer's size, weight or cost[1]. Plus opto-coupled arrangements are easily DC-coupled, no headaches with LF performance, a bugbear of NBTV and SSTV.
Steve A.
[1] I'm always thinking of commercial applications...
Harry Dalek wrote:...for a future monitor 100 lines (or) over .
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