Anyone know what this thing is? - Page 1
Forum section: electronics / projects

author: jeffheath
author_rank: Regular Contributor
timestamp: February 17, 2019, 05:03:39 am
content: Google turned no datasheets. Someone said I could have anything I wanted from their parts bin, so I chose this, because it looked cool.

author: pigrew
author_rank: Frequent Contributor
timestamp: February 17, 2019, 05:12:42 am
content: It's a DAC (digital to analog converter) made by the PMI company. The part number is DAC-01. It is a 6-bit design, and uses a R-2R ladder circuit.I found a few books containing datasheets for it:1986 PMI1976 PMIThe datasheet even has a photo of the top metal layer (attached).

author: jeffheath
author_rank: Regular Contributor
timestamp: February 17, 2019, 05:39:13 am
content: Quote from: pigrew on February 17, 2019, 05:12:42 amThanks! I guess I came to the right placeOut of all the uses on the datasheet, "telephone system digitizing" definitely sounds the coolest, I didn't know they were already doing that in 76.

author: KE5FX
author_rank: Super Contributor
timestamp: February 17, 2019, 05:41:35 am
content: Quote from: jeffheath on February 17, 2019, 05:39:13 amThey were doing that in46.

author: jeffheath
author_rank: Regular Contributor
timestamp: February 17, 2019, 06:30:20 am
content: Quote from: KE5FX on February 17, 2019, 05:41:35 amSo basically it was a6 bit dacwith a sampling rate of 50hz? I wonder what it sounded like...  could something like sigsaly even have bit depth?

author: KE5FX
author_rank: Super Contributor
timestamp: February 17, 2019, 08:12:09 am
content: Quote from: jeffheath on February 17, 2019, 06:30:20 amI can't imagine what that thing sounded like, or (especially) how it would have been synchronized.I hope someone eventually builds a full-fledged emulator so we can find out.It used a 6-bit DAC, but with thermometer codes instead of binary. Basically a compander.

author: Psi
author_rank: Super Contributor
timestamp: February 17, 2019, 11:24:38 am
content: Not that you would ever want to destroy something so nice, but here's an interesting fact...Those ceramic case metal-top ICs have a pretty high amount of actual gold in them, compared to modern ICs anyway.Can't be 100% sure as it doesn't have a glass window too look inside but a lot of them have the die attached to a gold metal braiding using gold solder and then there's the gold bond wires as well. Not to mention the metal top and pins are hardgold plated.They are very high up on the scrap value list. Probably only $1 of gold but that's a lot for a single IC.The king of IC's for gold recovery (excluding uncommon milspec/medical/RF stuff) is old ceramic Pentium Pro chips which contain around US$5-15 of gold each.

author: TurboTom
author_rank: Super Contributor
timestamp: February 17, 2019, 03:51:26 pm
content: Another, quite peculiar application of that DAC was as an RPM preset element in an all-electronic engine control unit of a tiny turbojet engine (of its time that is). See here:If you're interested in some more information on that particular engine (Williams Research WR24-7), have a look here:http://www.turbinenmuseum.de/Gasturbines/WR24-7-2/wr24-7-2.html

author: KE5FX
author_rank: Super Contributor
timestamp: February 17, 2019, 10:30:41 pm
content: Quote from: TurboTom on February 17, 2019, 03:51:26 pmIncredible stuff. How much thrust did the engine actually produce in the test, I wonder? I noticed the test stand was mounted on a wheeled cart, so it was somewhat disappointing not to see the cart zoom across the parking lot.

author: TurboTom
author_rank: Super Contributor
timestamp: February 17, 2019, 10:45:21 pm
content: We only ran the engine witout the tail pipe / nozzle assembly. In the particular run that we got on video, we also didn't reach full RPM (fuel feed issues), I guess the engine produced in that run round about 100lbs / 450N of thrust. In a later run, we reached 100% RPM but still ran it witout the tail pipe so actual thrust was probably approx. 80% of rated figures (so it must have been something like 180lbs / 800N. In that run, two men had to push the cart quite a little to keep it from moving...So far, it's a collector's item but eventually it will have to be used in some fun project...