Image Engineering “DV” laser show decoder to ADAT direct digital idea

This is mostly a documentation post trying to tie together some thoughts.

A few years ago I worked to reverse engineer schematics and operational theory of the Image Engineering DV decoder for video tapes with digital data of laser shows stored on them. These decoders demux 10 DACs worth of data stored on video tape to drive two color laser projectors.

I have a bunch of tapes, and I would like to archive the content before the tapes degrade.

My original research got me to the point where I found the clock and data coming into the portion of the circuit that demuxes it. But I never put a ton of time into getting a microcontroller to decode it since it requires using an interrupt to detect the break in timing to mark frame start — and once I do get the data moved to a computer I need a solid clocked format to store the content and that seemed problematic. (Tying it to a WAV file as sound card captures audio was one thought.)

Then I picked up a ILDA to ADAT converter from DZ/Ed O’Keefe. They’re awesome people from the laser show hobby/industry that make some nice converters. I was originally using modified ADAT to do this operation but wasn’t happy with signal levels, was out to get their ADAT to ILDA box to give me a nice reference to how things should work when I stumbled across the other version. Thinking more about it, and knowing a little bit about the chip in the box I got to thinking…. if I used parallel to serial shift registers in place of the ADCs I could wire the input side to read the data from the DACs in the decoder. The ADAT system (in my case a HD24) would be sampling the data at 48Khz and the DV playback systems runs slower.

Looking into the wavefront ADAT encoder IC, it doesn’t provide all of the clock signals to clock the ADC chips. I found some info on what could be the circuit needed to do the clock dividing:

In this case their clock is 44.1khz and I would rather run 48khz. Also, since I need 10 channels then two chips have to be wordclocked together and hopefully the ADAT is happy.

To keep cabling limited between the old board and any new board I was looking at the schematic I drew out in the past. It’s been 3 years and it took a bit to get back into it. Data bus + chip selects into something that can store state into some sorta shift register that is compatible with the data output of the ADCs that are normally used to feed the Wavefront AL1041AG chip:

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