Part 1 - Starting the Build

Part 1 - Building the Front Board and Motherboard

 

21 June 2023 The Front and Motherboard PCBs arrived and got stuck into populating it. As per normal practice the low profile parts first. Had to be very careful with the LEDs as they are not all orientated the same way. Switches not in yet as the plastic bit on some need to be swapped and the grey ones still need to be printed. Also going to print a support around the switches to help prevent cracking of the solder joint. Panel mounted switches would have been better.

This is the front board, all these LEDs come on without anything connected and actually works!!! Note: The other LEDs have the logic the other way round so need their respective pins grounded, did that and all work. Just haven't tested the one-shot circuit yet. So if nothing else I have an LED matrix board that could do pretty patterns, like those computers in in Star Trek (TOS)

It took a good few hours to finish as there was a lot of double checking of the values and the orientation of each part, hate desoldering stuff. But with that all done it was time to move onto the motherboard. This has only a few components only frustrating part is installing the longer JAMMA connectors. Nothing wrong with PCB or the connector its just a lot of pins (76) to line up. But all good now have to wait for the lost PCBs to be re-sent 😡. 

Building the Timer, Decoder and Accumulator

These three boards make up the next stage and when done some basic tests can be done. Page 26 runs through what tests can be done and involves some temporary cables between the front switches SR0-7 and MB0-7 that way the switches can pretend to be the MB register for a day.

Boards have their IC sockets and all the passives but ....

EDUC-8 Build

 

EDUC-8 Build Log

The trials and tribulations of building a computer from a magazine published 50 years ago

After watching many a tube videos on how to build a CPU from scratch. I remembered the curator at the ACMSWA mentioning a computer from the 70's that was published in the Electronics Australia. It was almost the first computer to be published, it was beaten by a few weeks. But that one had a microprocessor all in one chip. So was kind of cheating. 😝

Specifications:

• Complete stored program general purpose digital computer.
• 256 Bytes RAM
• Instructions and words 8 bit
• Serial processing with clock rates of 500kHz and 2Hz
• Instructions cycles 96uSec (500kHz) and 24sec (2Hz)*

*Just as a comparison the Intel Core i9-1190K can do 5.3 billion cycles per second (5.3GHz) but does not have a Fast/Slow switch on the front making the EDUC-8 a lot more flexible.

The Articles

• The original publication stretched over 13 months. By Christmas '74 you had yourself your very own computer!!!
• Aug. 1974: Build your own digital computer!
• Sep. 1974: Our do-it-yourself computer: how it works
• Oct. 1974: Our EDUC-8 computer: starting construction
• Nov. 1974: Building our computer: three more sections
• Dec. 1974: The EDUC-8 computer: getting it going - at last!
• Jan. 1975: EDUC-8: adding the input/output interface
• Feb. 1975: Programming your EDUC-8 microcomputer
• Mar. 1975: Interfacing EDUC-8 with punched paper tape
• Apr. 1975: Interfacing EDUC-8 with a Philips 60SR printer unit
• May. 1975: A full ASCII-type input keyboard for EDUC-8
• Jun. 1975: Teaching your EDUC-8 to play a melody
• Jul. 1975: Interfacing EDUC-8 to teleprinters & magnetic tape
• Aug. 1975: Interfacing a Burroughs self-scan display panel to your EDUC-8

Build Index

Part 1 - Starting the Build

Part 3 - Little bit of a mod already

Part 3 - Building the Timer, Decoder and Accumulator

Part 4 - The Testing

Getting the bits

See the full BOM here

This build uses the same 74 series described in the original articles thanks to Steven Pietrobon for the link to Unicorn Electronics. They have all the IC' required including the 9602 monostable one shot. By changing some of the resistor 74LS series ICs can be used Steven has done all the smart stuff here and is described on his page. Looks like there are no wiring changes. This covers the majority of end of live ICS but the 9602 and the RAM could be a problem. Going to experiment with using a 556 to replace the 9602 but the RAM could be a problem. Might have to look at a 5v microcontroller with enough inputs for the address lines, the data I/O and the control lines.

The vendors for the components are listed in the parts list but primary vendors are:

Altronics for all the passive components, the IC sockets and headers. There are 99 ICs so machine pin sockets x 99 = a lot of money if you have to buy them all but it would be better than trying to de-solder a rare and static sensitive IC from the board! If you don't have any lying around just pick the most expensive ICs and socket them i.e the 2125 RAM, 74259 latch, 9602 Multivibrator etc...

Unicorn Electronics for all the ICs they do have good prices but the freight is not cheap and slow USPS. The webpage looks like it was developed using MS Frontpage 1.1 😝 which I guess adds the experience.

Aliexpress for the JAMMA connectors. The ones here are used for Gwylln's boards. They are oversized for the actual cards but does mean you don't need to modify them. Also bought the front switches through them. They didn't have the Grey switches for the Single, Slow modes so will need to print them. Thingiverse have the drawing so just need to print. Suggest using a resin printer, better quality finish. And just to make it harder the red switches need to be toggle and could only find spring return so need to buy more black ones and swap the plastic part over.

JLCPCB for the PCBs Gyllwn has kindly included the Gerber files and this is all you need to get them made by JLCPCB. There are many PCB manufactures but this one has an easy to use web site and have CNC services. Yet to be tested but will probably get them to cut the front panel. Their freight is expensive and have a minimum buy of 5. Used the cheapest (SF Global) once and they lost it, so from now I going to use FedEx which is about $20 more.

Amazon have the 6-pin DIN sockets bought these with matching inline male connectors. Jaycar also sell the sockets but not the connectors.