Any one with "first hand" infomation on how hard is it to build a "computer",(?)

I did it three times way back, twice sucessfully.

First attempt was a 'traditional' computer box, with paddle switches on the front panel to input a bootstrap (EPROM was very expensive in those days). Mostly from trying to make it 'look nice' before I got a working board, the project never was finished. Looking back later, it had some chance of actually working.

The first to work was a CMOS computer based on the COSMAC processor. It was a kit computer, big PCB you stuffed maybe a dozen ICs into. Has 256 bytes of memory you could bootstrap off a hex keypad. Worked for years till the key switches gave up.

Last one was a Z80 system, 1K RAM, 2K EPROM (which was finally cheap enough to afford). It was a embedded controller thing to drive serial bussed relay drivers, with a decimal keypad (build out of a scraped keyboard), two 7 segments, and an 8 bit latch to drive the serial bus. Each relay was simulated with a dual FF and a LED. Code was hand assembled Z80 loaded into the EEPROM via a home built EPROM programmer running off a Sinclair computer (the first computer to break the $100 price barrier, an excellent thing it was).

If I was doing it today, I'd look for some single board computer as a starting place. Digi-key probably has some, or check any decent electronics magazine (Nuts and Volts may have some links online).

If you have any other comments back, start a new thread please, this topic deserves it.
Posted on 2003-03-30 12:52:34 by Ernie

what happens if you spill some on the floor? How do you know what is what afterwards?

I've had that problem half a dozen times. The first time it didn't matter, as I didn't know any of the values. The problem was to find info on the transistors - the text mark, that I could see, marked up 20 different types of transistors. Happily, my experiments showed it's a BFR93, that is hell of a transistor - something like BFR91, but in SMD. I ripped a handheld phone to get these parts, as I cannot buy any here.

Ah, :eek: and ... after one spills some on the floor :confused: , well, he saves some work, as most get lost :grin: .

Debugging is the process that takes a lot of time :mad: - getting those small 'breakpoints' is hell.
Posted on 2003-03-31 11:51:26 by Ultrano
Well the Microchip PIC processors are sweet little contollers with SRAM and Flash EEPROM built in. For fully embedded processors one very simple one is Intel's 80188 family. I prefer the 80L188EB which is a 3.3 volt processor with all the controllers built including an NS16450 compatible USART for serial communication. With this processor you still need external RAM and ROM. SRAM is suitable and Flash is good choice for PROM. Other than that it make a very simple glueless hardware environment and the instruction set is completely 8086 compatible with 1Meg memory addressability. You can download manuals from Intel Developers Network. The 386EX is another more powerful embedded processor they have.
Posted on 2003-05-04 18:36:18 by mrgone

A multimeter, I guess. :)

Well... I can just imagine how difficult it would be to make sure your multimeter probes don't short.
Posted on 2003-05-04 20:37:58 by AmkG
What happens if you spill some on the floor?

Well you find a broom, of course.
Posted on 2003-05-04 23:11:41 by Ernie
Anybody know where I can get a free router to make gerber files? I don't 9000 dollars right now for Orcad
Posted on 2003-05-05 00:25:03 by mrgone
How about this.

Posted on 2003-05-05 08:19:14 by minor28
Test drive it huh? Yeah I got a guy that Uses Orcad & Pads PCB who is top notch in this field and he still gets stuff wrong causing me extra board runs. I use Veiwmate to look at the Gerbers but had to catch everything like 0805 size caps etc. I think if I did Gerbers myself there wouldn't be anymore mistakes. I'll check it out though.
Posted on 2003-05-05 10:47:29 by mrgone