Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Yes Harry, the SSTV mechanical camera is still on my lengthy 'To Do' list. When will I get around to it? Who knows?
Other things are getting priority at the moment, and I still have the 5" CRT monitor/display to do as well as the 625-to-NBTV converter to finish.
But I'll be watching this thread with interest.
Steve A.
Steve Anderson wrote:It seems like you're getting there Harry, But I was surprised when you mentioned the slow response of the 4046 a few days back. You only need to use the VCO secion, simply ignore the phase comparators. I did knock one up a few years ago and had no real problems with it. I ran it at 16 times the normal SSTV frequencies (19.2kHz-36.8kHz), this then was fed into a 'walking ring' counter which produced a not-so-bad sine wave. Some simple filtering followed to clean up and remove the harmonics.
I don't have any circuits for it as it was done for amusment more than anything else, a 'see if it's possible' exercise.
I'm somewhat house-bound at the moment, I took a bit of a tumble down some stairs yesterday, so I have the time to have another fiddle with it.
Steve A.
Steve Anderson wrote:The circuit (00009.jpg) you posted could be quite easily changed to a single-supply version with a few changes to some of the components.
Somehow, although nice and simple, the unijunction oscillator probably isn't that linear, but better than nothing.
If you replaced it with the VCO section of a HEF4046 (not a HC version) you could eliminate the 74LS90 device, this would also remove the requirement for a +5V supply. Though if the rest of the system uses +5V it makes no difference.
There is a 'proper' symbol for a unijunction, I can't recall what it is though, I'll do a Google...OK, found...attached...
Though reading a few datasheets on these devices many manufacturers use a symbol which for all the world looks like a SCR.
I'll have a look at this a little later- I have a few things to do this morning first.
Steve A.
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