Another DIY ProFile emulator (but also: bridging 3.3V and 5V)

Anyone who's read Dr. Patrick Schäfer's excellent IDEfile project page
<http://john.ccac.rwth-aachen.de:8000/patrick/idefile.htm> knows that I
tried to make a ProFile emulator about eighteen years ago. And yeah, I didn't finish it---it was a bit too much for a class project :-)

I guess I never really gave up the challenge, though, because I've finally tried again, and this time I did it!

It's really part of a larger goal, though. I'm pretty excited about using tiny single-board computers like Raspberry Pi to interface with retro systems and "fill in" for peripherals and missing hardware. The BeagleBone Black and PocketBeagle <http://beagleboard.org/boards> are especially exciting little boards, since their integrated SOCs have co-processors called PRUs that can do very precise digital I/O in software. Earlier this year, someone used this capability to make an ethernet gateway for talking to a Xerox Alto
<http://www.righto.com/2018/01/xerox-altos-3-mbs-ethernet-building.html>!

The problem is that most of these boards use 3.3V logic, while most old systems deal in 5V. So, you need an extra bit of hardware that does the voltage translation. There are a few classic ways to do this, but lately I've been intrigued by the TXS0108E and TXB0108 series of chips, which do bidirectional voltage translation without needing to be told which direction the signal at each pin is going! I was curious to know if you could design a voltage translation board around these chips that would be general---you could use the same board for all kinds of projects with fairly minimal changes.

So, that's what I've tried to do, and my proof of concept is the old ProFile emulator again. Unlike last time, this time I had Dr. Schäfer's notes and all the archived docs on Bitsavers, and I couldn't have done it without those. I also assembled a UsbWidEx
<http://john.ccac.rwth-aachen.de:8000/patrick/UsbWidEx.htm> earlier this
year, which made testing and debugging much, much easier. Now that that's done, the thing seems to work pretty well. I haven't used it for too long, but it works with Office System versions 3.0 and 1.0, and also with the various backup and restore options provided by BLU and UsbWidEx. (I'd be really curious to know if it works on an Apple III.) It seems pretty fast, too---a little bit of a surprise since a big chunk of the code is just a Python script!

This project was a lot of fun to do, and it gives me a lot of hope for making these sorts of hardware substitutes easier for hobbyists to build. I hope there are lots of applications where one quick solution is to get a PocketBeagle and a board like mine and whip up a replacement for a missing piece.

None of this stuff is for sale, and I don't plan to go into the hardware-selling business, but all of my designs and source code are up on GitHub and released to the public domain. You can buy circuit boards from (e.g.) OSH Park <https://www.oshpark.com/shared_projects/51GWu9Kw> and make your own if you are OK at surface-mount soldering---the hardest part is getting those two TXS0108Es in place. If you do try it, just remember that everything about this is early beta at beast; I'm a software engineer, not an EE! :-)

Here are links:
http://github.com/stepleton/cameo
http://github.com/stepleton/cameo/tree/master/aphid

and here is a silly video if you want to see it in action: https://youtu.be/1nYteAcB7Jk

Hope this is useful,
--Tom

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