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Revision Updates & New Parts of the Spec

A project log for Retro Modules

Production-Ready Modular Prototypes using Hardy Connectors of Yesteryear

yesnoio 08/17/2015 at 06:570 Comments

After the Maker Fair 2015 revisions were adopted, I went back to work updating a bunch of Retro Modules which were no longer in compliance. This is one of the reasons I'm striving toward a stable pin specification in short order. It is not fun looking at a box full of no-longer-compliant modules. I've had to sift through existing modules to find the few which were not affected by the spec revisions. Thankfully, I am gaining momentum again.
When I built out the hardware for my 'Christmas Truck' project, I used the Retro Modules spec extensively. Those modules will need slight updates now, but even the basic modularity of the install proved useful. I recently traded my truck in for another, and the uninstall process was a breeze. That is -- everything except some of the oldest modifications I made to the truck. The 2012 Tacoma features a LCD screen in the rear-view mirror. It, at times, displays composite video from the stock rear-view camera. I wanted a way to send my own video to the mirror without making a big mess of the mirror housing. I was able to locate the video cable & make a splice quite some time ago. To undo this splice, I had to break out the soldering iron & solder the short segment of wire back together. If I decide to do a similar modification today, I would make it easy to remove any mods. How? I would add connectors (blade, etc) which allow the stock cable to be reconnected to itself with ease. This can increase the cost of the mod, but not by much.

Headers

I have spent some more time fleshing out pin header specs & documentation. The very common 26 pin header is hardware compatible with a 25 pin DB-25 connector. The 10 pin header is compatible with the DE-9 connector. This allows the use of old-fashioned header-to-connector ribbon cables. You may have had some of these cables in an older desktop tower.

"AC'97"/"HD Audio"

Another common staple of desktop computing is the "AC'97"/"HD Audio" header & breakout modules. Many modern single-board computers feature analog & digital audio, but are often broken out via consumer audio jacks. These small computers could leverage the AC'97 header with great ease -- reducing circuit-board complexity & increasing design flexibility. A source of confusion for many, however, is S/PDIF headers on motherboards. Legacy graphics cards often shipped with a tiny cable for routing digital audio. S/PDIF headers are not well standardized & may consist of two to eight pins. Given this problem, I opted to append five pins to the end of the "AC'97"/"HD Audio" header. This keeps compatibility with off-the-shelf desktop audio modules yet allows S/PDIF in/out on a custom header if so desired.


Pro audio is also an important area to focus on.

Since part of this spec features analog audio next to other digital signals, there is a greater risk of noise. Many environments do not require pristine audio conditions. Some do. This is why I have included support -- in certain connectors -- for AES Digital Audio. S/PDIF is the consumer version of AES. AES42 has some really great features that quite a few sound engineers enjoy. These signals are generally sent on a standard 3-pin XLR connector. There is risk, though, in sending digital signals on a connector primarily used for analog audio. Audio mixers may get damaged if a AES signal is connected to an analog input. I have proposed a spec for 6-pin IEC XLR connectors to hopefully address this issue -- and add a feature or two. The 3-pin connector only allows for one-way transmission of digital audio signals (generally). A 6-pin connector allows for power & bi-directional AES transmission. This opens up doors for chainable digital effects processors, digital audio pedals, mics & remote monitoring. For instance, an artist performing on stage generally needs a mic, guitar input & monitor mix. This could be accomplished via this single XLR cable. The monitor mix would arrive on the `digital-audio-aes-host-out-client-in` pins, and the audio source(s) on-stage would be sent back to the mixer via the `digital-audio-aes-client-out-host-in` pins. These on-stage modules could be powered via the `fourty-eight-volts-max` pin.


This latest work can be seen on the incoming branch of retrospec.cc.

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