[sdiy] SMPTE Time Code Reader—Need Generator

[S Ridley]

There's a decent explanation of SMPTE 12M timecode here:

http://www.philrees.co.uk/articles/timecode.htm

It was developed around 1967, so meant to decoded by hardware.

Typical older systems I've worked on use brute force - a PLL clocking the
timecode into a 80 or 160 bit long shift register.
At each end of the shift reg, a decoder looks for the sync word - forward
at one end, backwards at the other, so it knows if the tape and therefore
the timecode is running backwards.
When it sees the sync word and knows which way the code is going and it's
position,  it  grabs the BCD data for each digit and displays it - or
whatever.

The input is effectively audio into the XLR - horrible noise - bleeds
though onto stuff.  Good multitrack practice was to put TC on track 24, and
put the bass on track 23 so you could filter off any TC bleedthrough.
The ancillary out will most likely be user bits and maybe the drop frame
flag.  I suppose it might also indicate tape speed (from the PLL) and TC
error / unreadable (drop-out, spooling too fast etc). .


Steve







On Sat, 15 Jun 2024 at 23:43, Terry Bowman via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Edited to add image...
>
> On Jun 15, 2024, at 6:34 PM, Terry Bowman <ka4hjh at gmail.com> wrote:
>
> The next question is how do I feed the audio into the gadget? Here's what
> the rear looks like:
>
>
> Oops, no pictures on SDIY.  <facepalm>. Here it is
>
> https://imgur.com/a/PypB9e9
>
>
> What's with that five pin XLR? I assume it's the audio code signal input
> but what are the other lines for? The switches are power and frame
> indicator on/off and the auxiliary output is connected directly to some
> chips on the board.
>
> I'm seeing multiple cathodes lit at once so it may also be the case that
> the LM74141 (Soviet K155ИД1) Nixie drivers are shot, no surprise there. And
> I broke a leg off of one of the chips while reseating them so I guess I'll
> have to scrounge around for a replacement. May have to be 74LS.
>
>
>
> Terry Bowman, KA4HJH
> "The Mac Doctor"
>
> https://www.astarcloseup.com
>
> Q: Should car stereo speakers be pointed to the rear for more thrust or up
> for more traction?
>
> A. On long trips, the 20- to 30% improvement in gas mileage you might get
> with speakers pointing to the rear is certainly worthwhile. On the other
> hand, if you drive on snow or ice, the extra traction of speakers pointing
> upward gives you added control.
>
> Don Lancaster
>
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