test-drb July 2007

test-drb@ccmp.vtda.org

189 participants
323 discussions

Replacement NorthStar Horizon Wooden Case Covers

by lynchaj＠yahoo.com

Hi, If you are interested in purchasing a replacement wooden case cover for a NorthStar Horizon computer, please contact me. Thank you. Andrew Lynch

17 years, 1 month

cctalk Digest, Vol 47, Issue 30, message 30, identify a capacitor

by mike＠brickfieldspark.org

> Message: 30 > Date: Tue, 17 Jul 2007 17:16:16 -0600 > From: "Michael B. Brutman" <mbbrutman-cctalk at brutman.com> > Subject: Re: Help identifying a capacitor > Some of what I'm reading says put the capacitor near the power supply, > and other things are saying get it as close to the chip as possible. > > The board I posted about is not optimal in this regard. It's an ISA bus > to PCjr bus adapter, so there is no TTL logic anywhere on the board - > the individual ISA cards have the TTL (and hopefully bypass capacitors). > In this application was the designer just trying to 'clean up' the > voltage sources for the TTL on the cards a little bit? > >From some years in pcb design shop. Bulk decoupling where the power enters the board 10-100uF + 0.1uF. Then a 0.01-0.1uF per Ic (for TTL that is). Keep the traces from the power pins to caps as short and fat as possible. Powers should ideally be planes or gridded traces. Newer logic families / packaging (TQFP, PLCC Etc), usually have very specific decoupling requirements set my the manufacturer

17 years, 1 month

[personal] cctalk Digest, Vol 47, Issue 29, Message 9 Subject: LEO (1950)

by mike＠brickfieldspark.org

> Message: 9 > Date: Tue, 17 Jul 2007 10:29:07 +0100 > From: Rob <robert at irrelevant.com> > Subject: Re: Vol 47, Issue 28, message 10, Subject: LEO (1950) > To: "General Discussion: On-Topic and Off-Topic Posts" > > .. except i had a sudden thought, and checked, and in the couple of > years since I last drove past the site, a Tesco supermarket has > apparently sprung up... Neither multimap.com or google earth > satellite photos have yet caught up... > > Sigh.. > Tescos are killing our computer history - ? to qualify - The National Gas Turbine Establishment (NGTE, Farnborough) has been partially derilict for the last 10 years or so, on that site were an Elliott 803B, SDS9300, DEC PDP-7 and 11-05, and more, I helped maintain them. Tesco wants to build a 1,000,000 sq ft distribution depot, apparently it will be one of the biggest buildings in the Uk,.with 1600 38 ton lorry (non motorway) movements a day, nothing good will come of it. I'd love to get hold of the PDP7.

17 years, 1 month

[personal] cctalk Digest, Vol 47, Issue 30 Capacitor ident

by mike＠brickfieldspark.org

> I'm trying to reverse engineer a board that I have and I've bumped into > a component that I don't understand the markings on. If you would like > to help, a picture can be found here: > > http://brutman.com/2007_0717_124331.JPG > That is a Tanatalum bead capacitor, 1uF 35V Dc rating, the + is for the +ve lead, which is a different length to the -ve lead when the component is new before soldering. 104 is 10 +0000 pf, 100,000 pf, 0.1uF, voltage rating unknown but probably in the 50Vdc-63Vac range. A common pairing for bulk decoupling on power lines or planes.

17 years, 1 month

TTL homebrew CPUs

by julesrichardsonuk＠yahoo.co.uk

I've been thinking more and more this last week about designing a CPU to be built from TTL logic ICs, purely as an interesting exercise. I'm thinking of a microprogrammed design with a pretty minimal register count - but as speed is never going to be a defining aspect anyway using commodity TTL, I'm thinking of going for a bit-serial ALU to keep the parts count down. Keeping the raw components pretty basic is another desired goal - no custom off-the-shelf ALU chips, gate arrays etc. Questions: have any others on here done stuff like this, or have any pointers to good resources? I'm learning as I go along here, flicking through technical manuals for 8-bit CPUs etc. and gleaning what I can from the web. MAGIC-1 is about the most comprehensive online resource I've found so far, but I believe it's a pure parallel core, and plus it's *way* more feature-rich that what I'm aiming for. I'm not interested in running UNIX-a-like software, or giving it hard drive interfaces or network stacks - I just think it'd perhaps be fun to design and later build something from scratch to do basic computation. cheers Jules

17 years, 1 month

1966 Mag: Build NE-2 Neon Bulb Computer - scan available

by ajp166＠bellatlantic.net

> >Subject: Re: 1966 Mag: Build NE-2 Neon Bulb Computer - scan available > From: woodelf <bfranchuk at jetnet.ab.ca> > Date: Tue, 17 Jul 2007 12:22:41 -0600 > To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org> > >Bob Bradlee wrote: > >> And never dialing Zero! >> otherwise an operator error will occure :) >Drat... I can't get all the parts. :) >Where do you get a telephone dial now days ... If I got the >phone with a dial it would work better than the $10 one I have. >The neon bulbs may be hard to find , the ones now days have >a built in resistor. A dial comes from an old phone, check a thrift. The NE-2s are still very available from most decent electronic parts suppliers. The trick to age NE-2s is run them at 50% over rated for a week (at lest 40 hours) and they will stabilize nicely. If you need to grade/match the aged NE-2s a 500hz relaxation osc and a scope will allow viewing the upper (fire voltage) and lower (extinguish) voltage as well as sensitivity to light very quickly. Hint, light should be incandecsent or the osc will try to sync on the flourescent flicker. Allison

17 years, 1 month

Help identifying a capacitor

by compoobah＠valleyimplants.com

> Is there a > good tutorial somewhere that explains how capacitors are used for > decoupling and smoothing? (I've checked some obvious sources, but I > need more detail, like if you connect a cap to a +5 source and ground, > why doesn't it just discharge completely ...) > Look at a book dealing with the design of PSUs, or a introductory electronics course. The basic rundown is this: Capacitors and inductors have reactance across them when fed A.C. Reactance is an opposing force that works against the flow of current, in this respect it's similar to resistance, but resistance is the same across all frequencies, reactance varies (for a given reactive load, X(L) (inductive reactance) goes up as frequency increases, X(c) (capacitive reactance) goes down. Impedance is the combination of reactance+resistance. For a DC supply with ripple, you can think of it as 2 mixed components: a DC component and an AC component. The capacitive reactance is chosen to present a low impedance path to the AC component so it travels through the capacitor rather than into the chip. Inductive reactance figures in because (as mentioned) the traces have inductance, and the capacitor also has inductance (so a large capacitor to smooth a high-frequency AC component might not be the best choice- all of that metal provides inductance that opposes the flow of the AC component). Help any?

17 years, 1 month

crimp-on D-sub pin removal

by compoobah＠valleyimplants.com

> Nowadays I might consider making yet another adapter and rewire the > modular side by using a cat5 patch cord and a dual modular jack, wiring > the jack with the crosswires as necesary. requires very little by the > way of tools, and keeps everything else original. I would have considered that had these been anything special, but I got a bunch of these adaptors from my dad's dental office when they were moving off of their Xenix system (with the Xenix system as well). They are not wired to any standard I know of, and they don't even seem to be wired to the same standard within the lot. I remember fervently wishing that they had used a MicroVAX instead of a PC with SCO. I also wished that I had been paying attention when they were getting rid of the Altos, but that was when I was in 4th grade.

17 years, 1 month

crimp-on D-sub pin removal

by compoobah＠valleyimplants.com

I am somewhat flummoxed- I have a 8-pin modular to DB-25 adaptor that I need to move some pins on to make if functional with a 3B2 machine, but looking at the unused connector positions I can't figure out what the retention device is for the installed pins to remove them. It doesn't look like a Molex-style clip coming from the pin (2 pins are uninserted) and there doesn't seem to be any catches molded into the plastic. Any pointers on how to pull these pins with standard garage tools?

17 years, 1 month

crimp-on D-sub pin removal

by compoobah＠valleyimplants.com

> Only if your garage comes standard with the D-series pin puller tool. > :) > > If you've seen the tool for some variant of molex connector, you've > seen > the principle: a thin-walled split tube which slides down around the > pin, inside the socket, and shoves the plastic retainer bits out of the > way. > > For a picture: > > http://www.tecratools.com/product1199.html > > De The picture didn't help much, but the basic description did (I've never used a Molex pin removal tool, every Molex I've worked on has succumbed to a dental pick in short order). It is possible to remove these with basic garage tools: all you need are a small piece of thin sheet aluminum and a moderate precision 5/64" metal dowel- in short an aluminum soda pop can and a 5/64 drill. Form the aluminum into a tube with a slot suitable for 24 ga wire, put around the pin, pull out- all in less time than it takes to drive to the semi-local electronics store.

17 years, 1 month

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test-drb July 2007