Interak Z80 Computer

A Z80 based computer, modular in design. Well build and thought out.

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This is a very old and yet newish project. Back in the late 1980's I began to build a Z80 based computer. The Interak, produced by Greenbank electronics in Liverpool, the attraction for me was you could build it bit by bit, board by board, It fitted in a 3U high 19" rack, you could jump on it without harming it, built like a tank.. I had many years of fun and learning my basic electronics with it. But then I sold it a few years later and got my first PC. About 2 years ago now someone discovered it in a rubbish skip in cambridge (along with a CPM book with my details inside), I had sold it to a company out there. and i was able own it once again..... so I've turned full circle, with a lot of other stuff between.. Pics and Arduinos tec..

In the early days programs, like on other "HOME" computers were saved and loaded our programs to/from a standard cassette recorder, this seemed to work fairly well, but on some machines a program saved on a hot day, may not load on a cold day. The clock frequency (often a simple NE555 circuit ) drifted with temprature. The Interak circuit was much better then this, using an AY-3-1015 UART, dual TAPE output and relays to switch the recorder motor on and off.

It was not until we had Floopy drives  3.5" 720Kb that we had a choice of Basics and Pascal, "C" etc.  This all ran under CP/M 2.2. Which we still use, even if it's now on a Compact Flash card, with 16 x 8Mb drives...

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  • New Video display and PCB's

    mel07/03/2020 at 10:46 1 comment

    29/09/2020. The good news breaks! the first of the  NEW designed PCB's are available, these are the Ram/Rom card, with boot eprom or EErom and a full 64K of Ram. The I/O-RNG card is a general I/O card with a Random Number Genarator. Also included is a large proto-typing area, for your own I/O ideas.

    New PCB's for building this Super project are now available, the first two are:

    ROM/RAM :

    I/O RNG :


    See the FILES tag for schematics and support files, more detail.

    It's now June 2020 and Alan Paton has redesigned the 80 Column VDU card, I have built it so we are both running a typical CP/M system of the time. Alan also revamped the Programmable Graphics Card. I likewise followed and built it. Now a new body in the form of Julian Winpenny has come along and is getting some proper PCB's made for these, they may also be of interest to many other Z80 users with a memory mapped display. I Will keep you informed...... Mel.

    Update 20/08/2020 Julian is now designing new boards for the Z80/CF card, Ram/Rom and I/O boards, which includes a random number generator. So a complete new Interak system is now available. These are super 4 layer boards, gold plated where needed. The good thing about the Interak is it can be whatever you want it to be (Quote: David Parkins), and these boards allow you to build it!!  I'll add the board details and schematics, etc under the Files tag.  Mel.

    I hope you are all well and keeping safe, in these difficult times.

  • Minor Interak meeting 27/10/2019.

    mel10/28/2019 at 15:28 0 comments

    27/10/2019. Well today a few of us got together for a chat and to meet for the first time. We met at the Retro Computer Museum here in Leicester, they came from everywhere like Liverpool and Wiltshire to mention 2.  We had 4 very different Interak computers there, some working better then others.

    A very nice cased system that Greenbank did for BT, My interak in the background and Andy's far right, trying to fix a floppy disk controller card.

    Alan's Interak is one of the best I've seen, not that I've seen many. The case has extra height, good for displays.  see:   My old Interak site is at

    And lastly all of us. Keith Parkins, Andy Collins, Me, David Parkings and Alan Paton

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david wrote 10/28/2023 at 14:48 point

Just finished building my interak , all up and running ! Does anyone know how to mount the cp/m bin file on windows or linux to transfer files or alternatively how to use the cp/m FT utility to copy files via serial ?  

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Jomac_uk wrote 04/05/2023 at 23:40 point

I'm not sure if I am asking in the right place, but would anyone have or know where I can get the CTS256A-AL2 text to speech IC?

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Dave's Dev Lab wrote 01/29/2021 at 22:51 point

hey there! was the VDU based on an existing design? i've been comparing it to the original MDA/CGA boards for the IBM PC and see some timing differences.... 

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Alistair wrote 12/21/2020 at 22:26 point

Joy to the world an Interak is born. I finally "finished" building the Interak I started 30+ years ago. I say "finished", it's only a 4 card minimum system (using original hardware) but it works! Are there any Interak forums or groups? I have a long and boring story and a laundry list of questions. :-)

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mel wrote 01/07/2021 at 16:11 point

Hi Alistair, it;s good to hear from you, yes most of us started 30-40 years ago. Only in the last year have we added an whole lot of new PCB's (Sorry to say be some of the old designs have stuck) But going from floppies to a CF card system with 14 drives of 8Mb each is lots for an 8 bit system.  If you send your email details to me at: I can add you to the list (a short one) and you can join in with us and see what we say or do!  we're here to help.

Best wishes.


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Sam Swain wrote 01/17/2022 at 16:40 point

Ooh, would you be ok to add me too? I've been looking for some Interak contacts. It'd be great to set up a forum or something for this.

I recently resurrected the Interak my dad built 40 years ago (and I coded a ton on). Dug it out recently and it's now my hobby (again). Check out this thread for the 'unearthing process' and occasional updates.

I'm currently working on squirting commands/data at it from my PC via the keyboard port (I want to keep interactions as non-intrusive as possible).



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Rob Welsh wrote 11/07/2020 at 00:43 point


There is a typo in the bill of materials for the CPU-Compact Flash Card....... R5 is listed as a 10K resistor and it should actually be a 4K7 resistor.

I`ve just started a full new build with Julian`s brilliant PCB`s as I got hold of a mint original rack with backplane and PSU.... I`ll keep you posted how it goes ! :-)


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nexxo00 wrote 11/08/2019 at 20:43 point

(tears up) It's so beautiful!

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alcmcintosh wrote 11/07/2019 at 01:27 point

Nice! Just looked at a Z-80 cpu card with 64K memory with the Motorola 6845(?) Video chip. Also have a batch of programs to support it. Had plans to add a 256 byte paging system. Had the card connected to a minicomputer for mass storage and downloading the os and app programs. Mostly assembly programs.  Card is wire wrapped. Nice to see there is still an interest in the Z-80...

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mel wrote 11/07/2019 at 09:09 point

Hi alcmcintosh! I like it.  I am just looking at on old Elektor cct for an 80 col VDU also using the MC6845, 64 cols at present but most CP/M stuff is for an 80 col screen. also need programmable graphics. We have schematics etc..

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Gerhard Schmidt wrote 11/06/2019 at 21:40 point

Hi. Looks like my homebrewed 1984 Orwell-Z80-system with ORWELL-DOS operating system in assembler, with ten Euro-size cards, 64-pin bus-system, 8-inch-Floppy-controller, 512*512-pixel B/W graphic controller,  4*32 k EPROM for the operating system, 4*8 k SRAM for battery-buffered data and 32 k dynamic RAM for data.  See for the hardware (in German only). brgs, gsc

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Jim Thompson wrote 11/06/2019 at 18:10 point

Do you know if the physical arrangement is compatible with Eurorack (the modular music synthesizer system)?  (5.08 mm (0.2") horizontal spacing between centers of 3 mm threaded holes, and 122.5 mm (4.82") between centers vertical spacing.)  It LOOKS the same, aside from depth from the front panel, which is much greater than most Eurorack cards, and I think that Eurorack got its physical arrangement from generic card mounting boxes produced in the 1980s.

I've been toying with the idea of using Eurorack for amateur radio modules (VFOs, synthesizers, IF strips, mixers, audio preamps and amps, using better connectors (no 3.5mm plugs for RF!!)), and it would be great if a microcomputer standard fit into the same physical space.  Do you know what type of connectors are used?  And are these on ribbon cables (like Eurorack), or are they on a backplane that dictates a particular card depth?  I mean, it SEEMS like even if there is a standard depth, the backplane could be implemented with ribbon cable - just a thought.

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bert.hoogenboom wrote 11/06/2019 at 19:30 point

There many card racks of this kind 19 inch wide 3HU means the cards that fit in there are 100 x 160 mm

I used this rack in 1980 to build a z80 system that is still working today

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Neil Johnson wrote 11/08/2019 at 10:03 point

Eurorack (the synthesizer format) is based on the Eurocard subframe format as used by these computers.  Dieter just used standard parts from the likes of Rittal, Schroff, etc, to keep costs down.

What these rack mount computers use is a common backplane to carry power and the address/data/control lines between the various cards (CPU, IO, VDU, floppy, etc).  This is how this case system is supposed to be used.  The Interak uses an edge connector backplane, the alternative is the DIN41612 connectors, which are also typically mounted on a backplane (see VMEBus or STEBus systems).

The Eurocard format (100mm x 160mm) is designed to exactly fit into these frames and support an DIN41612 connector to the backplane.  There is a wide variety of DIN41612-compatible connectors, some up to 96 pins, some with RF connectors, some with power spades, and some have combinations of all of these.

19in subracks are used extensively in the comms world.  So amateur radio should feel right at home there!

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julian wrote 11/05/2019 at 11:41 point

Mine's been in the shed for 18 years - just starting to power it all back up (cautiously).

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Dan Maloney wrote 10/23/2019 at 15:49 point

You had me at rack mount...

I never heard of this one at all. That modular design is cool. Looking forward to progress.

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