Building Computers

[MDZhB]

I'm not sure if this is the right place, because everything here seems to be related to space travel, but this is the science forum.

Does anyone have experience with building electronics? I'm talking the kind of home made computers like one would see in the 70's or 80's, built around something like a 6502 or z80.

If so, how did you acquire the skills and knowledge necessary to do such projects? I am certain I can do it, and I want to, but I don't really know where to look for information outside of documentation on parts themselves (datasheets, manuals, etc.), or even what to look for.

Could anyone point me (and hypothetical future readers) in the right direction?

[stibbons]

My first year comp eng course ran right the way through. Started at boolean logic, and progressed to designing and building a simple 8 bit computer in a logic simulator. That was the mid-90s and my recollection of it is hazy at best, but I'm pretty sure I still have the textbook kicking around at home.

Buy a book. Something like https://www.amazon.com/Elements-Computing-Systems-Building-Principles/dp/0262640686/ looks like it would be a good primer. Alternatively, my five minute skim of http://www.instructables.com/id/How-to-Build-an-8-Bit-Computer/ says that it seems to be an alright overview of basic overall design.

[MDZhB]

13 minutes ago, stibbons said:

Buy a book. Something like https://www.amazon.com/Elements-Computing-Systems-Building-Principles/dp/0262640686/ looks like it would be a good primer. Alternatively, my five minute skim of http://www.instructables.com/id/How-to-Build-an-8-Bit-Computer/ says that it seems to be an alright overview of basic overall design.

Wow. This is pretty much exactly the kind of info I'm looking for, and I can't believe I didn't find that instructable earlier. Everything I have found thus far seems to build off of the kind of knowledge presented in those.

Unfortunately, I don't have the money for a book at the moment (I already bought one on a completely different subject!) but I am reading the article now. I know (or think I know) about the microprocessors, boolean logic, binary, etc., and I can get information relatively easily on the physical side of things, but putting those two together is where I'm struggling a bit.

[Nuke]

this gal put together has a 6502 retro computer named veronica, complete with build log, schematics and some asm code. she built the whole thing from scratch and stuffed it into an old timey radio, though she did cheat and use some modern microcontrollers for things like video generation. totally worth a read.

Edited June 30, 2016 by Nuke

[kiwi1960]

Oh wow..... I was born in 1960 and I remember making a Z80 based computer back in the 70's...

That takes me back.... wow.... now you made me feel old.

Yep. and books would be the way to go... but before you start, make sure your soldering skills are up to the task.

Nothing worse than a splotched gob of solder shorting out two connections.... or worse, a dry joint.

Good luck.

Edited June 30, 2016 by kiwi1960

[wumpus]

The first thing I would suggest you learn about is wire wrap.  As the name implies, it is a means of connecting wires by simply wrapping the exposed conductor around a terminal several times.  Quick to attach and de-attach, it is a favorite means of prototyping (especially at the frequencies 6502 and Z-80 operate at, much less useful with modern gear).  I've seen plenty of older computers that were *shipped* using wire wrap, so it isn't just a "cheap hobbyist" method.

While wire wrap is great, expect to learn how to solder.  It takes a little practice and the basics involve heating both sides hot enough so that when you apply the solder to them (not the iron), the solder melts and flows on them.  Don't get the leads to chips too hot.  A good solder joint is shiny (well used to be, I'm less sure with modern silver-based solder).

When I was introduced to professional electronics, my professor forced us to by textbooks (which seemed expensive at the time, but nothing compared to now), mostly to assign homework.  We were told that the text book was sort of right, the book containing the data sheets was supposed to be right, but the actual computer (much like the cat in psych) was *always* right.  A quick test is often easier to do and harder to misunderstand than reading through a datasheet.  Still, you need to know how to do the test and a higher level book is a good place to start.

Books from that era are almost certainly out of print (although "Soul of a New Machine" is probably good for inspiration, and almost certainly available).  Go through a used bookstore and see if you can find anything that looks good from that era (I scored a "TTL databook" once.  While absolutely nobody builds anything that it describes, the current stuff all has the same pinout and is largely backwards compatible).  One thing that should cover the basics is https://www.amazon.com/Bebop-Boolean-Boogie-Third-Unconventional/dp/1856175073 (note this is third edition.  The second edition lists a $12  used book (might not include shipping) and is certainly written since 2000, thus not being a problem).

For PCB design, I certainly would recommend downloading the Eagle CAD package.  While it completely lacks the polish of professional CAD, it should be able to get the design done.  You can also build something like 10cm by 10cm boards (check before starting) without paying anything for this software (and smaller circuit boards will always be cheaper to have manufactured anyway).

Assembling a circuit board can be more tricky.  One small startup I worked at had built circuit boards by manually placing parts on the board and then cooking the whole thing in a toaster oven.  I never got the hang of placing the tiniest components, but an earlier guy could.  Note that there are a lot of hidden costs in this, as you need things like solder mask stencils to have something to stick you components on and cook (and don't use a toaster oven for food that has cooked lead).

If you want to get really creative and build your computer from the architecture up, I'd recommend looking into FPGAs.  In any event, I'd look into FPGAs and CPLDs if only to reduce part count.  Basically, this is a way to design your own chip in "software".  Typical ways to program involve languages like Verilog and VHDL and the chip vendors probably have *something* you can download and convert into the necessary bitstream (although they will be designed primarily to work with some seriously expensive software).  Also learn what microcode is/was.  Microcode basically lets you program a pile of chips to be a computer, and was the basis of computer design until things like Verilog and VHDL could compile down to a whole chip (microcode took up a lot of a few of my electrical engineering classes at school and at least on professor quoted a computer designer as "never making another non-microcoded computer".  Microcode was effectively obsolete by the time I graduated, but still used in the dark corners of modern Intel machines for all those instructions that haven't been used since the 90s).  If this seems like cheating and not sufficiently "hardcore" compared to using your soldering iron, don't forget that the pros in "Soul of a New Machine" were half "microkids" who were doing the microcode and the hardware guys were slapping down "PAL here" (a CPLD forerunner) every time they needed something complicated.

For overall computer design, as far as I know "the book" is still Hennesy and Patterson: Computer Architecture, a Quantitative Approach.  Note that it is used in graduate level classes as well as upper level undergraduate courses, so you might be spending some time in the first few chapters furiously trying to build up the background.  It isn't cheap, but sufficiently advanced libraries should have earlier editions (I'd expect current ones to be checked out by students).  They also wrote an introductory book called Computer Organization and Design, and if you can get it first I'd recommend it.  Unfortunately I bought it after studying the first and was greatly disappointed (so I really don't know if it is any good or not).

And don't try to build anything huge as your first soldering project.  The lessons KSP teaches you about fake rocket design carry well over into other design fields.  Make sure whatever you build is small enough that you can figure out why it doesn't work.  When engineers first apply power to a design it is called a "smoke test".  If no smoke comes out of the device, they are happy.  They often don't expect it to work.  Then the real work goes into discovering exactly what it is doing and adjusting the design/manufacturing so that it does what it is supposed to, and iterate from there.  If you have multiple errors in you device (design flaws plus soldering globs plus unsoldered pins) it will be vastly harder to troubleshoot than a single failure (which can often be divided and conquered, no matter how invisible the error).

PS: I remain convinced the the "best" architecture for that era would have been a stack-based architecture with a fairly large DRAM array on chip.  The point of a stack architecture would be for the single addressing (both one source and destination would typically be top of stack) so that a single word would come off the DRAM array (you can only use DRAM if you can deal with only one port).  The DRAM array would be useful for other things, as an instruction/loop buffer (probably too small for a real cache), for a stack buffer, and (tiny) data cache.  Not sure if fast page memory would be early enough to make it make sense (it needs *some* form of burst memory reading), but it would certainly hit a brick wall around the time multiple issue RISC designs came out (early 90s), so perhaps we are better off without such a design.

[MDZhB]

10 hours ago, wumpus said:

The first thing I would suggest you learn about is [snip]

Your post was a long one but I read it all! This is the exact kind of information that I'm looking for. Again, I unfortunately don't have a lot of money right now, but I definitely have some books on my shopping list now...

 

[MircoMars]

4 hours ago, MDZhB said:

I unfortunately don't have a lot of money right now, but I definitely have some books on my shopping list

do you have a library nearby? either a public or a school lib could have the books you're looking for. other possibility would be a second hand bookshop or yard sale or flea market. all fittingly old school for what you're looking for. perhaps you'll even find some old hardware there, for parts, inspiration etc

[wumpus]

4 hours ago, MircoMars said:

do you have a library nearby? either a public or a school lib could have the books you're looking for. other possibility would be a second hand bookshop or yard sale or flea market. all fittingly old school for what you're looking for. perhaps you'll even find some old hardware there, for parts, inspiration etc

Remember, if you are targeting old hardware (you can do a lot more with a soldering iron or wire wrap at a few MHz, GHz is right out), you should be able to find things in a library (also hopefully significantly marked down in a used bookstore, but that might be better for browsing and reference books).  You might want to try an inter-library loan or something, ask a librarian (I know there was a copy of Bebop to the Boolean Boogie in a library 30km south of me, but I doubt there are any in the system I have a card for).

Also note that costs of building the hardware can be all over the place.  The cost to pay the engineers to design such a full computer board (even for fairly small computers) can easily be over a million dollars, so "reasonable support services" can be very pricey, but worth it to those who are happy to shave a few days off the budget.  Don't be to fixed in assuming there is a certain way to build something (some of those "pricey" services have a lot of competition and you might afford to build a small board done in a modern way that you could never troubleshoot if done by hand).

[Xorth Tanovar]

On 6/29/2016 at 11:07 PM, kiwi1960 said:

Oh wow..... I was born in 1960 and I remember making a Z80 based computer back in the 70's...

That takes me back.... wow.... now you made me feel old.

Yep. and books would be the way to go... but before you start, make sure your soldering skills are up to the task.

Nothing worse than a splotched gob of solder shorting out two connections.... or worse, a dry joint.

Good luck.

Sinclair ZX-81 kit, by any chance?

Put one of those together in high school, freshman year electronics class.

[MDZhB]

5 hours ago, MircoMars said:

do you have a library nearby? either a public or a school lib could have the books you're looking for. other possibility would be a second hand bookshop or yard sale or flea market. all fittingly old school for what you're looking for. perhaps you'll even find some old hardware there, for parts, inspiration etc

 

41 minutes ago, wumpus said:

Remember, if you are targeting old hardware (you can do a lot more with a soldering iron or wire wrap at a few MHz, GHz is right out), you should be able to find things in a library (also hopefully significantly marked down in a used bookstore, but that might be better for browsing and reference books).  You might want to try an inter-library loan or something, ask a librarian

These are all good ideas, but I live in a relatively small rural area, so the libraries are tiny. I know the school library doesn't have anything, and I haven't looked at the public library (for this material) yet, but I suspect the same thing. I think my only option would be an inter library loan.

That being said, nothing is impossible! I'll double check to be sure. Thanks for all the advice guys!

[kiwi1960]

7 hours ago, Xorth Tanovar said:

Sinclair ZX-81 kit, by any chance?

Put one of those together in high school, freshman year electronics class.

Not quite, after I built my "toy" (compared to what we have now, it was!) I actually bought a ZX80, then a ZX81 ... then a Spectrum 48K and the a Sinclair QL ....

I also owned a various other toys, such as the CBM64 and the like.

I actually believed Uncle Clive (Sinclair) when he said you could run a nuclear power station with a ZX81 ... I added "provided you only want to turn a single light bulb off and on with it"

The toy I built was part of my training for both the Computer Electronics Course I was doing, and as a project to help decipher Morse Code for my Amateur (Ham) Licence.

[MDZhB]

I wish I could get some older computers, (the closest I have is an old Windows 98 laptop, and it's not even mine). They're difficult to find, and when you do find them people either don't want to give them away for any price, or they want a lot of money for them. Sentimental reasons, I guess.

Also, I'm glad they took the Morse requirement out of the ham exams, I would have never made it.

Edited July 1, 2016 by MDZhB

[Camacha]

9 hours ago, MDZhB said:

These are all good ideas, but I live in a relatively small rural area, so the libraries are tiny. I know the school library doesn't have anything, and I haven't looked at the public library (for this material) yet, but I suspect the same thing. I think my only option would be an inter library loan.

The modern era provides you with a world wide web with insane amounts of information, so be sure to start digging. People just 20 years ago would have killed for what is out there at the click of (mouse)button.

Also, getting hardware does not have to be expensive. You can buy a cheap soldering station and stuff like a breadboard, some wires, components and ICs (mostly from China) on Ebay. That should get you started for not much money at all. Another wonder of the modern age

 

[SgtSomeone]

Not quite sure how it relates to the hardware you referenced, but if you're interested in some of the lowest level stuff, turns out Minecraft's Redstone circuits are actually pretty good for basic logic exercises. You can start with a basic binary calculator, and there are some people who've built the registers, CPUs, and RAM to model basic computers! 

 

[Camacha]

2 minutes ago, SgtSomeone said:

Not quite sure how it relates to the hardware you referenced, but if you're interested in some of the lowest level stuff, turns out Minecraft's Redstone circuits are actually pretty good for basic logic exercises. You can start with a basic binary calculator, and there are some people who've built the registers, CPUs, and RAM to model basic computers! 

If it is basic logic you want, there is a whole host of dedicated software out there Though I have not used it much, I liked Cedar.

[K^2]

On 6/30/2016 at 8:46 AM, wumpus said:

A good solder joint is shiny (well used to be, I'm less sure with modern silver-based solder).

Still want it shiny. Mate surface is a bad sign on solder no matter the material. It's another matter if it doesn't happen as frequently with some solder types, and that shiny surface alone might not guarantee a good joint.

[Nuke]

i for one still use the 30 year old mega roll of solder i sort of pilfered from my grandpas shed sometime after he kicked the bucket. i get superior joints to any kind of solder ive bought at radioshack or online. ive heard stories about how solder can "go bad" but i just dont see that as having any basis in reality.

Edited July 3, 2016 by Nuke