Closed Caption Decoder

After doing a little research, I learned that the text is sent in line 21 of the video signal encoded as regular ASCII. I'm thinking, "Hey, no problem" and I started designing the circuit. Of course I used a Z80 with the usual RAM, EPROM, etc. I used a Zilog SCC chip for the serial ports because of the built in Phase Locked Loop circuit that it has in the clock section. That would make it a lot easier to "lock on" to the data, I figured.

Unfortunately, the analog/video portion of the circuit kind of got out of hand, what with me having a mainly digital background. I kept adding more and more parts until I finally got a decent looking signal to send into the SCC. I was real concerned about the timing of the sync pulse which told the SCC when to start assembling the data bytes. As it turned out, the timing wasn't at all critical (thanks to the Phase Locked Loop). What was critical however, was the comparator voltage that I used to convert the analog signal into a stream of digital data. Every time I changed the channel, I would have to readjust the comparator level. Someday I'll have to put in some kind of AGC circuit or something, but for now, I just live with it.

So once I had valid CC text coming out of one port of the SCC, all the processor had to do was strip out the control characters and send it back out the other serial port, which used a MAX232 chip to generate regular RS-232 levels. This is then connected to any computer running a terminal program with logging capability, and viola.

I have only run into two problems by using this approach to creating transcripts. And in order to explain them, it now becomes necessary to reveal the true reason I built this project: Star Trek transcripts. Yes, I am now admitting it, I am a Trekkie or Trekker or whatever they call it. Anyway, my goal was to have all the transcripts for all the shows (ST:TNG in this case) on my PC, and then, use tools like "grep" to search for stuff. You know, stuff. Like, in what episode did someone use the word "anthropomorphizing". Stuff like that. Which brings me to my first problem. A lot of the time, closed captions only paraphrase what the actor says onscreen. I'm not sure if this is due to ad libbing on the part of the actor, or what, but in any case, I wanted accurate transcripts. So I ended up manually editing the text later to make it match the actual dialog.

The second problem is a legal one. The closed captions on every show always say that "public performances of closed caption are prohibited" or something like that. So even though I'm sitting on accurate transcripts for ST:TNG for seasons 2-6, (I got sick of doing it after a while) I'm not about to post them here, for fear of being sued by Paramount or somebody. But at least I can find out who said "anthropomorphizing" if I need to.