A TTL Computer? A recent Goodwill Find

thumb_board_close_upI came across the device pictured here recently at Goodwill (a thrift store) for a few bucks.  It looked interesting and potentially useful.  I hope you enjoy the pictures and ponder as I did who might have built this - it appears to be a TTL-based microcontroller or maybe it's just an interface to something else.  There are no markings at all apart from the calibration sticker, and it reveals nothing about the history of this device.

What you see in the pictures is all I know about this device.  Since it has no labels or other identification, I suspect it was built by a hobbyist like many of us here.  If anybody can shed some light on this device, I'd appreciate it.

mt_ignore:top_viewTop Panel. Note the Load/Prgm....switch.

mt_ignore:bottom_viewBottom side. No markings but note the quarter-turn fasteners hold the case together.

mt_ignore:end_viewSide view of the DB-25 interface connector.

mt_ignore:cal_stickerThe only identification on the enclosure, a calibration sticker.

What's Inside..

So the outside is kind of intriguing, but sure doesn't reveal much about what's inside!

mt_ignore:PCB_-_frontWow, a circuit built on Vectorboard with TTL parts.

mt_ignore:board_close_upHere's a closeup of the board. Many of the chips are 74LS-series which does help put a time-frame on the construction.

mt_ignore:board_backsideHere's the bottom side of the board showing the wire-wrap construction. Imagine making all those connections and not getting anything connected to the wrong pin. Wire-wrap wasn't limited to hobbyists. For many years I used a spectrum analyzer that was all wire-wrap construction. It had 10 or more large boards filled with chips.

mt_ignore:wiring_aidNote the wiring aid to keep the pin numbers straight when working from the back.

mt_ignore:inside_panel_1The inside of the front panel shows some nice assembly details.




I hope you've enjoyed the pictures.  Really makes you appreciate the powerful devices we use today, bread boards and cheap circuit boards!

Posted: 8 years 8 months ago by Graham Mitchell #5483
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You've found a relic, that much can be confirmed!

It looks to be a purpose built test aid of some description. The controls suggest that sequences could be programmed which allow a degree of automation for different Units Under Test (UUTs). Perhaps the program feature extends the functionality to several different types of UUTs?

The counter on the lower left corner suggests it has been used at least 8000 times - Someone out there would be very familiar with it!
Posted: 8 years 8 months ago by andyo #5484
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Nice find. What are the bundles of wire wrapped together with - it looks like they're tied together with bits of string??
Posted: 8 years 8 months ago by Jon Chandler #5485
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The "counter" at the bottom is actually a bank of BCD thumb-wheel switches.

The cable bundles are tied with lacing string. It's like wide waxed dental floss. The ARRL books used to have an entire section on cable lacing. Here's a Wikipedia link.: en.wikipedia.org/.../...

An interesting point...the clock and the strobe bits have banana jacks...but there's no ground or common jack.

Graham, the format edits look good. Thank you.
Posted: 8 years 5 months ago by techmonkey #7357
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Here is my theory. This device looks like you can use it to write or read a register or memory bank one byte at a time. "Load" setting proably loads from preset pattern chosen witht the BCD wheels. "Program" probably takes the binary values of the switches and saves them as a programmed value into local memory. "Set" may be to ssend the values into the device under test as a sequence and runs it. "Singele Set" does the sequence once. "Pattern" loads a patterninto the device and then reads it back to compare if there were any bit errors. "Stop" should be obvious.

The jacks are probably just breakouts for a scope or logic analyzer, the real interface to the DUT is the DB25. I bet this unit was built custom by a professional test house. I saw this kind of assembly on older testers while building legacy military electronics. Heck, you still see wire wrap on some newer custom stuff as long as it is not high speed.

Where did you pick it up geographically? Maybe I can narrow it down as to who owned it.
Posted: 8 years 5 months ago by Graham Mitchell #7373
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Hi Techmonkey, welcome to Digital DIY. I imagine Jon picked it up somewhere near Seattle WA, USA (his profile location). Might be wrong
Posted: 8 years 5 months ago by Jon Chandler #7364
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Exactly right Graham. There are many possible sources around here including The Boeing Company, Puget Sound Naval Shipyard and a huge number of scientific/electronics related companies. A government organization like the shipyard or a large commercial organization like Boeing will usually have more distinctive calibration stickers. I think it's going to remain a curiosity until I decide to use the enclosure for something else.
Posted: 8 years 5 months ago by techmonkey #7368
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Funny thing is, it kind of reminds me of how a professor of mine programmed a naval gunnery computer when he was in the Navy in the '70s. They would do war games and a ship would take a simulated hit and electrical would go out. This would wipe the memory of the targeting computer and it would have to be reprogrammed, by hand. The programmer consisted of a row of 8 switches and a push button for entering each instruction. If you made a mistake, you had to power cycle the system and start over. He said the fastest person he knew could do it in less than 20 minutes because he could do it from memory. After a couple of years, they got a tape backup

This thing could even be a debugger for that system.
Posted: 8 years 5 months ago by jmessina #7374
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It was a common technique back in the day. That's how we used to have to boot up the PDP8 (http://en.wikipedia.org/wiki/File:PDP_8_e_Trondheim.jpg).

It's amazing how fast you can get flipping switches and punching buttons once the sequence gets ingrained in your brain.
Posted: 8 years 5 months ago by be80be #7371
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There no way that thing was made for the Navy It doesn't have a $1500.00 dollar hammer in it.
Posted: 8 years 5 months ago by Jon Chandler #7372
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There no way that thing was made for the Navy It doesn't have a $1500.00 dollar hammer in it.

While it probably wasn't used by the navy (wrong type of calibration sticker) it could have been. Yes, things delivered to the military under large contracts can have the gold-plated toilet seat effect, not everything they use must follow the same pattern.

I worked for Puget Sound Naval Shipyard for 10 years. During my time there, I built a lot if instrumentation to make our job easier. We were in a "poor stepchild" support group and always had a tight budget, so much of our test gear was made on the cheap.

Two specific examples come to mind. The first was a switch box / power supply for accelerometers with integrated electronics. The $1000 tri-axial accelerometer required an interface to the $15,000 2-track tape recorder. Since it was used for testing on ships, size and weight were important considerations. There wasn't actually any commercially-available gear to do what we needed in a decent-sized package.

The accelerometer needed 3 constant current power supplies delivering 5 mA with an 18 volt potential. If you look at the LED tester I posted yesterday, the very same circuit with LM7805s (purchased at RadioShack out of my pocket) was used. Power was provided by 2 9V batteries. And the whole device was housed in a plastic VCR tape case, which happened to fit perfectly in a pouch on the tape recorder. All-told with connectors and the rotary switch, less than $50 was invested in that project.

The other example may be interesting to some people. Pardon me if this gets a bit long. One of our jobs was to record vibration readings on shipboard machinery prior to overhaul and after overhaul to evaluate machinery condition to plan the repair package and document condition at the end of overhaul. A seven-track magnetic tape recorder was used to record 2 tri-axial accelerometers from several locations on about 150 machines. A quick look was taken at each machine during testing but detailed analysis was done after the trial in the office. The result of the survey was 3 or 4 CASES of magnetic tape which required about 3 man-weeks to playback and process into vibration signatures (~3000 plots) Tedious and mind-numbing work. Then the process of data analysis could finally begin.

A contractor we knew also did these surveys but they automated the data reduction. They used an encoder to record DTFM (telephone touch tones) at the beginning and end of each recording which allowed automatic data reduction back in the office. Someone had to babysit the recorder as the tape automatically shuffled back and forth as the data was played back; periodically, the reel of tape was removed and swapped for a new one.

Slick system. It removed much of the tedium and reduced the time until data analysis could begin. I envied the system, but the encoder/decoder cost more than $10k and it wasn't in our budget no matter how much time it would save. Then the idea hit me! I couldn't get an encoder like theirs but I could get a 300 baud modem for next to nothing! This would not only encode a recording number on the tape, but could also encode machine information, positions, recorder and amplifier settings and all the other information normally recorded in a log book! I did some tests, and sure enough, data recorded on a tape track from the modem could be accurately read from the tape! Awesome.

Still, with no budget and management who didn't always have clear visions about how things could work, I set about building a system. Mostly on my own time and mostly with whatever parts I could find or purchase myself. I'll save you (most) of the details. Our encoder started life as an Atari 300 baud acoustic modem (yep, the kind you stuck the telephone handset in) which I traded a box of 50 generic 5" floppy disks for. I put together the encoding system and data acquisition side of the system and demonstrated it to management. They finally saw the light and authorized some time work on the data reduction/playback side of the system.

I was in awe the first time we used the system (and actually every time we used it after that). Put the first real of tape on the recorder and press go. Tape starts spinning and reads the data off the minute-long recording. The tape recorder reversed. Spectral data for channel 1 appears on the analyzer, followed by the remaining tracks. The tape shuffled back and forth until all the tracks were processed and on to the next recording. Roughly 45 minutes later, the reel is done and needed to be changed. Meanwhile, a second computer was monitoring data files and plotting out the graphs as each record was finished. Wow.

The results were impressive. Data processing time was reduced from 3 man-weeks to 16 hours! Instead of a pile of hand-plotted and labeled graphs, nicely printed graphs that could be re-printed later if needed. So what was the cost to achieve these awesome results? Some billable time was used. A box of my generic floppies...and a $4999 bonus (split 3 ways) for me and the two others who helped make this a reality.

The Atari-modem based encoder didn't look too different from the TTL-computer. It was in an aluminum enclosure designed for Vector boards that I found stashed in a drawer, which I spray painted just about the same blue color as the TTL-computer box!

Yes, a long story but many folks who work for the military are skilled technicians and create devices to make their jobs easier all the time at little or no cost.

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