Skin of Many Colours

Posted on October 29, 2020 by admin

I was having a chat with a friend of mine, Tony Davies of DCS Electronics in the UK. We were discussing possible expansions for the ZX Spectrum and arrived at a system of plug in modules for experimentation and utility. I commented that it would be a little like ByteDelight’s Speccy Breadboard but with different features.

Tony and I hashed out the idea and I began designing the board. I based the outline on the successful ZX Diag Cart sold by ByteDelight since I had the original files to hand and lots of people said they had appreciated the two indents on the board allowing easy removal from the rear of the Spectrum.

During our discussions, Tony and I decided that we could forgo the video signals from the rear edge connector and most of the voltages. We reasoned that any small projects or peripherals could use the Spectrum’s internal +5v and anything needing more current could use the raw +9v from the Spectrum’s power supply and regulate to taste.

We christened it ZX Chameleon due to that fact it can change it’s character (or colour) depending on the use it was put to. I retained the NMI and RESET buttons from the Diag Cart since there was enough room and they were already part of the original design.

Having designed the carrier board, it was time to go ahead with some sort of expansion module. I settled on a prototyping board because I’d attempted this once before and been unsuccessful. This board took a long time to lay out and clean up but I think it was worth it. I modelled it on a regular breadboard with added ground lines and voltage connections available.

The board allows for a couple of ICs placed in the center and plenty of space for discreet components. The connections to the Spectrum are easily connected from the rows of connections next to the headers.

It was around this time when I re-read ByteDelight’s product description for their Speccy Breadboard. I was struck by how similar the designs and intent was. Despite having designed the Chameleon from the ground up effectively. Tony and I have since chatted to Ben of ByteDelight and he is happy to sell the Chameleon and expansion boards along with DCS Electronics.

A first run of boards has been ordered and will be duly put through their paces. In the meantime, you can currently pre-order the boards on the DCS Electronics website.

We are hoping that this will be a great platform for experimenting and useful expansions for the Sinclair ZX Spectrum. If you have any ideas for module units, please contact me through the usual channels.

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Straight Through

Posted on April 6, 2020 by admin

With the delivery of the Sinclair Spectrum Next in full swing for the first Kickstarter, several owners have reported a small problem when using peripherals. Some edge connectors partially obscure the HDMI port on the ‘Next when connected.

To alleviate this, I designed a through connector extender. It pushes the rear edge connector back allowing HDMI connection. I have also included expansion facilities in the way of a set of header pins. This can be utilised in different ways to connect to other interfaces.

Adaptor Connected

I have prototyped the first run in ‘ProjectSPECCY’ red but the production version will be black in keeping with the ‘Next’s aesthetic. This is a development of the Spectrum Backplane, and in common, it is a straight through connector. This means that despite it being designed for the Next, it can also be used with any Sinclair Spectrum model and also clones, provided they have a standard edge connector.

The expansion connections can be used in different ways. For instance, you can solder a header (male) in and mount a short edge connector type PCB to mount vertical interfaces. Or you could fit a header socket and solder the edge connector PCB to the header plug and use it as a vertical adaptor or remove to connect your own peripherals.

Once the prototype has been proved, I’ll be selling the adaptor on Tindie in two versions. One with just the pre-soldered edge connector and one with the added connectors for expansion.

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Testing….testing…

Posted on May 20, 2019 by admin

For a while, I’ve been working on an update to a popular diagnostic board for the Sinclair Spectrum range of computers. The original design was by Dylan Smith and has been through several periods of development in the past. I have had one of the older versions for a few years and it is really useful, especially when loaded with suitable diagnostic software such as Brendan Alford’s.

Original Diagnostic Board (Right) Along Side the Newer Prototype.

I asked lots of the more knowledgeable Spectrum users in the Facebook groups what features would be useful in an updated board and the most popular was indicators for the voltage lines. The original board, pictured in yellow above, has 8 LEDs to indicate if a Bit in lower RAM is faulty, if any, even if there is no display available. They also display interrupt addresses. The LEDs are driven by software. The other update requested was +2a/2b and +3 compatibility. The older board only works on 16/48K Rubber Key and Plus, 128K Plus “Toast Rack” and +2 grey machines.

For the update, I thought it would be useful to monitor ongoing activity on the data bus. While I was at it, I reasoned, surely it would be useful to see activity on some of the Z80 control lines too? I asked around again and compiled a list of the 8 most requested. They ended up being: M1, NMI, ROMCS, IORQ, MREQ, RD, WR and RESET.

To test the operation of the data bus and control line monitors, I used a simple 555 board (published on www.projectvir.com) to pulse the CLK lines appropriately. It worked very well and I eventually incorporated an SMD 555 circuit directly on the board. The switch in the top left of the board selects either Software control or the 555 oscillator as a clock for the data line indicators. The control line indicators are driven from the 555 oscillator all the time.

555 Pulse Circuit Installed.

I had already included the switch to change the clock lines for the data bus LEDs over to the Spectrum’s CLK line but this pulsed way to fast to see any changes in the LEDs, so the 555 fixed that problem. Although the 555 Pulse circuit doesn’t allow real-time monitoring, it does show activity on each of the lines adequately for most diagnosis needs. It is also customisable for duty cycle at build time.

Running Brendan’s software, there is a small issue when connected to the +2a/2b and +3 machines. The software runs correctly until it gets to paging back the Spectrum’s usual ROM and dropping in to the BASIC Menu. Instead it crashes the machine, showing the typical screen indicating no ROM is available.

Development will continue in order to track down the fault and once fixed and working, the design files will be available on the projects page.

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Magnum Opus

Posted on March 24, 2019 by admin

A lot has been going on in the last month. It’s been chaotic. The SoftROM continues to be a problem and is being investigated. So far, the toggle switches are suspected of bouncing, but even after smoothing that out, the device is still flaky. Investigation continues.

A while ago, I managed to pick up an Opus Discovery One disk drive. A large metal cased device that adds several features to your Spectrum 48K. The main one being a Double Sided Single Density disk drive. This was fine for way back when, but most modern users upgrade the unit. I’m no exception in this and as soon as I could, I ordered an upgrade kit from ByteDelight that included the extended RAM for use with HD disk drives, and a new QuickDos ROM v2.13. The upgrade kit is also available with one or two disk drives, but I already had one ready to go.

I also wanted to include a Gotek Floppy Disk emulator that I’d had for a while. This required flashing new firmware. I like the excellent FlashFloppy by Keir Fraser. The flashing of the firmware is pretty easy. Although I first tried using a USB to USB link, this didn’t appear to work very well in my case so I moved to the tried and tested Serial to USB technique and it worked first time.

FlashFloppy gives the ability to use many types of disk image and also enables you to customise the hardware with a very nice OLED display, Rotary Encoder for selection of files and even a piezo buzzer to make a noise like a real floppy drive!

Previous Gotek Customisation

As you can see in the image above from my previous Gotek Customisation, it creates a really cool device. FlashFloppy, at the time of writing this, is up to version 2.2. With the new drive, I wanted to do an extra neat job of installing the new hardware, so I took my time and created a 3D Printed bracket to hold the display at the right height. You can download it from my Thingiverse account to print yourself.

Gotek OLED Display Bracket Installed

The bracket, once fixed in (I used Hot Glue) allows you to simply slide the display into the correct position. A small dab of hot glue on the back of the display will secure it. I also used the option to flip the display and use the narrow text so that the aperture on the Gotek didn’t have to be modified at all.

Installation in the ‘Discovery case was a bit of a pain. Because the case had been designed with older SSSD drives, the mounting holes were incorrectly spaced and in the wrong position. I had to drill two new holes for each of the 1.44Mb Floppy Drive and Gotek. I also had to make up a straight 34-way to 34-way cable to connect in the Gotek to the second internal drive connector. I did this by taking a traditional floppy drive cable and adding an IDC connector before cutting the excess cable off. If you carry out this installation for yourself, pay attention to the orientation of the IDC connector and also the direction it plugs in on the PCB. I found that the original cable was fixed in backwards. This cannot be changed since the connector on the original cable is a transition type and is soldered down but doesn’t affect operation.

Cleaning the Mica Heatsink Washer

My ‘Discovery unit had obviously been opened before and the regulator removed and replaced. This meant that there was a lack of heatsink compound on both the bracket and the mica washer. Before rebuilding the case, I cleaned the bracket, the mica washer and the regulator tab with IPA (Isopropyl Alcohol) and applied fresh compound.

Finally, I remounted the plate carrying the drives and tested it. The worst thing is to close the case only to find that, for some reason, the unit isn’t working! Yes, I have done this before 🙂 After a successful test, carefully avoiding the mains on the exposed transformer! I replaced the case.

HD Floppy Disk Drive and Gotek Installed

I had found an archive of disk images to try out the drives with, so I formatted a floppy disk and copied over the files from the Gotek disk image for a test. I chose Outlet issue 14. It copied over faultlessly and ran from the floppy disk as it should. There are many more disk images to explore!

User Maryjan at Speccy.pl has been working on recreating the Opus Discovery One PCB and has done a stellar job of it. I am lucky enough to have one of his early boards (Cheers Maryjan!) and intend to build it as time and finances allow. It is incredible that we have access to the tools to duplicate our old technology so that it can be enjoyed into the future.

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Mikro Managing

Posted on February 18, 2019 by admin

After having the PCBs laying around for a long time, and with a little help, I have finally got the Shadow of the Unicorn Interface to work. The problem was right in front of me all the time and it took a conversation with my friend Russ to realise what was going on.

For those who don’t already know, the Shadow Of The Unicorn interface was meant to revolutionise the ZX Spectrum’s software catalogue by using the 16K of memory space usually inhabited by the Spectrum’s own BASIC Rom allowing larger, better games. Unfortunately, the end product was rather high priced and became the deathknell of it’s publisher, Mikro-Gen (who had earlier success with titles such as Pajamarama and Everyone’s a Wally).

Mikro-Gen’s Shadow of the Unicorn

The interface is wired for convenience to enable the original designer to create a one sided PCB. This means that the Address and Data lines were scrambled on the board. This, as I realised, required an obfuscated (Scrambled) ROM image to work correctly. It didn’t help that the ROM images that were available online had been previously unscrambled for use with emulators.

With a little help from the Spectrum community on Facebook and my friend Russ, I obtained a scrambled ROM and the interface sprang to life!

Finished Shadow of the Unicorn Interface
Finished Shadow of the Unicorn Interface

So, after languishing on my shelves for a while, the interface is now working and I have published both the design files and the scrambled ROM image on the Projects page for anyone to make thier own and enjoy the game.

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Darwin Would Be Proud…

Posted on January 22, 2019 by admin

I thought I’d post a short update:

The Backplane adaptor boards have arrived and I have tested one. It works fine. I’ve posted the design files on the Project page. In case you missed the previous post, this new board allows standard interfaces to fit on the Backplane vertically as they would with the Spectrum or Interface One rear edge connector. Some interfaces will need to be fitted to the third of forth slot on the Backplane to miss the on board regulator.

Horizontal Adaptor

The special project I’m working on has been a little troublesome. Making a few small mistakes on the first schematic didn’t help. One of the mistakes was to use a 16-pin DIP socket for a 14-pin IC. This meant that all the connections ‘rolled around’ the chip and meant that I had to make a patch to see if I could get the board working. This is when I discovered a further mistake that I had made in tracing the circuit. All the joys of reverse engineering!

The Offending IC Socket
The Offending IC Socket

I have now updated the board and have it working to a point. I think that either one of the ICs is faulty or I may have transcribed one or more other connections incorrectly. It is a fairly complicated circuit built on a home made two sided board with wire vias. Investigation continues.

Another development; My recreated SPEC-MATE stopped working. It took me a while to discover why it repeatedly crashed the machine it was attached to when the NMI button was pressed. It turned out to be a corrupted EPROM. This is despite having an opaque sticker over the exposure window. I think the EPROM was just suffering with age. Once I’d programmed and fitted a new one, it worked correctly again.

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Adapt & Evolve

Posted on January 2, 2019 by admin

Having now published the Spectrum Backplane (Which can be found on the Projects page), I thought it was time to update the expansion connections. I have a few interfaces that have edge connectors that lay the device down horizontally, but most interfaces have connectors that make them stand vertically. To enable use of these interfaces, I’ve designed a board to make an easy connection to the Backplane.

Horizontal Backplane Extender
Horizontal Backplane Extender

A set of pin headers will be soldered to this board and then an interface will mount as usual. This assembly can then be plugged into the Backplane via the expansion pin header positions. The PCBs are currently being fabricated and the design files will be posted on the Projects page once proved.

Meanwhile, I’ve been working on another very special project. This one, I will keep under wraps until I know it is operational. I am just waiting for the final few components to arrive before assembly and testing. I’m very much looking forward to sharing the design files – More on this very soon!

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Round Again

Posted on December 19, 2018 by admin

It’s been more than a year since I posted on this site. Quite amazing how time files! I had a bit of a Speccy burn Out and needed a break. This turned into a protracted period as I got interested in other things including Cryptocurrency and 3D Printing.

I didn’t forget about things Spectrum though and I’ve been keeping tabs on the Spectrum Facebook groups. I also been awaiting the dispatch of my fully boxed Spectrum Next. From the latest kickstarter update, it sounds like it’s almost there. Just a few things to finish up.

Meanwhile, my quest for a SPEC-MATE is finally over! Davide Barlotti, one of my Facebook contacts, graciously loaned me his SPEC-MATE on long term loan. Unfortunately, it conincided with my period of being quiet on the whole Spectrum front and I put it safely on my shelf. Quite recently, Davide requested I send his interface back, which I duly did. I very much appreciate his trust in sending it to me and letting me hold it for so long.

Literally, the day before I sent the package to Davide, he advised me of a SPEC-MATE availabe on eBay. It was insanely expensive, but due to the rarity, I snapped it up. I knew that I would be very unlikely to find another.

SPEC-MATE Snapshot Interface
SPEC-MATE Snapshot Interface

Once the SPEC-MATE arrived, I did a basic test on my trusty 48K Spectrum and it checked out. the next thing I did was to extract the EPROM to see if it had a different firmware version to Davide’s. Alas, it was the same. I then set about stripping the interface down and tracing the circuit. This was aided by Andy Lewis via Twitter, who’s one and only tweet was to send me the SPEC-MATE schematic. This allowed me to quickly trace and verify the circuit.

Andy Lewis’s SPEC-MATE Schematic.

I then set about designing a PCB. I kept it as small as I could and made sure to include four mounting holes. This is because I’d like to design it a case that can be 3D Printed. I also made provision for right-angled and flat trigger buttons so the interface can be orientated either upright or flat.

The boards duly arrived from JLCPCB.com and I built one up. Again, basic tests show the board is working, although I want to verify operation with Sinclair Microdrives and design a case before I publish the files in the projects section.

UPDATE: Device tested, case design is ongoing. You can find all the files on the Projects Page.

The Finished Recreated SPEC-MATE

This has been a long, drawn out quest for me. I’ve been wanting to own a SPEC-MATE since I became re-interested in Sinclair Spectrums a few years ago due to the ‘Next. I’m very pleased that I can share my files and enable anyone to build and try one out.

My thanks and sincere appreciation go to Davide Barlotti for the long term loan and Andy Lewis for sending me his SPEC-MATE schematic.

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Backplane again

Posted on November 27, 2017 by admin

I received the second version of the Spectrum Backplane the other day. I have since built one up and tested it briefly and it looks like it’s all OK.

Spectrum Backplane v2.00 - EasyEDA Gerber View

Spectrum Backplane v2.00 – EasyEDA Preview

This issue with the first one was that the front edge connector, the one that goes into the Spectrum, was inverted. That’s to say all the top connections were on the bottom and all the bottom ones on top. This meant that nothing could have worked, and indeed, I damaged my ZX-HD Display Interface assuming I had routed the backplane correctly the first time! I re-routed the front edge connector to fix this issue and now, all seems well.

Spectrum Backplane v2.00 With Vertical Adaptor

Spectrum Backplane v2.00 With Vertical Adaptor

I have created a vertical adaptor for plugging expansion interfaces in to the expansion positions. This consists of a small board soldered on to a row of header pins. The adaptor in the above image has missing pins where the slot is (Position 5). This is because I am intending to put polarising keys in that position in the socket holes to prevent expansion boards being plugged in the wrong way round. Additionally, there are two passthrough connectors, one on the left side and one on the rear, where you can plug in regular interfaces.

The +5 Volt line can be routed straight from the rear of the Spectrum or set to the external Traco driven power supply on the backplane via a jumper. The Traco unit requires at least 6 Volts to work and can supply 1.5A of current.

The reset button takes the /RESET line to ground, cold starting the Spectrum upon release. There is also a red LED to indicate power being fed into the back plane from an external source.

Spectrum Backplane v2.00 With ZX-HD and DivMMC EnJOY! PRO ONE

Spectrum Backplane v2.00 With ZX-HD and DivMMC EnJOY! PRO ONE

I have had several conversations regarding buffers, or lack thereof. Having tested the backplane with the ZX-HD Display interface on the rear, I’m not sure buffers are required for signal purposes. However, they may be useful for protecting the Spectrum. I will look further into this as time permits.

Another question is whether I will be making kits. The answer to this is no, I’m not intending to produce a kit or supply ready built back planes, but as always, the design files will be available on the Projects page for anyone to use in due course.

Hopefully, the backplane will open the way for some interesting expansion interfaces. I am working on a simple 8-bit I/O port based on a circuit published online by Grant Searle.

Another project I have been waiting to build is the Multiface 3 Clone documented on El Hardware Del Spectrum A friend of mine recently got a Spectrum +2A and commented that they would like a Multiface upon seeing my Multiface 128 recreation. Due to a happy coincedence of me spotting a post on the AmiBay forum, I managed to secure two bare PCBs to build up.

Multiface 3 Clone

Multiface 3 Clone

At first, after constructing the first one of two, I could not get the interface to work. The LED lit to show that the interface had been triggered when the NMI button was pressed but nothing happened. The LED even extinguished upon resetting the machine it was mounted on. I double checked the ROM and GAL and then swapped out all the other chips. All seemed fine and this stumped me for a few days. I had also double checked the soldering for splashes/shorts.

After re-reading an e-mail trail with the PCB supplier, I realised that I’d fitted a 100nf capacitor instead of a 1nf. After changing this component out, the interface worked perfectly, displaying the menu as normal! They say the devil is in the detail…

Fully built Multiface 3 Clones can be purchased on AmiBay from DJCook.

 

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Suffering with Backplane

Posted on November 11, 2017 by admin

Excuse the awful pun but I wanted to post about one of my recent projects. Back when I used to buy the great Spectrum magazines like Your Spectrum and Crash, I read an article about adding peripherals to the rear edge connector with a device called a Back Plane. I managed to find the article in a collection of YS magazines I bought on CD.

Your Spectrum Issue 18 (Pages 20/21)

Your Spectrum Issue 18 (Pages 20/21)

I had always remembered this image and recently, wondered if I could build a modern variation.

I determined that the best way to go, for the first iteration anyway, was to design a PCB with straight through connections. This would mean that it would be compatible with all Spectrum models, including the new Spectrum Next. I was aware that the internal 7805 regulator used for powering the Spectrum and it’s associated peripherals might be a little under-powered to cope with much more than a few added devices so I made provision for an external power source too. One final touch was to add a reset switch. Mostly because it’s an easy thing to add.

I had used KiCad library parts to make previous interfaces so I went ahead and used them again. I didn’t want to have a board as long as the one illustrated in the YS article so I shortened it a little. I use a ZX-HD display interface at the moment, in lieu of having a suitable Composite Monitor so I knew I’d need at least one pass-through connector. In the end, I decided on two.

I plan to make several other interfaces to fit on the backplane so a way of connecting them easily was vital. On the YS illustrated backplane, the board has sockets which add-on boards plug into. I thought this might be a little limiting, especially for interfaces that already exist. What I have used is rows of header pins that can be used directly with ribbon cable or fitted with an extra board to emulate the Spectrum’s rear edge connector. These extra boards will be soldered on to the header pins to make a permanent extra ‘Edges’ to mount horizontal interfaces on.

Spectrum Backplane v2.00

Spectrum Backplane v2.00

Edge Connector Extender Board

Edge Connector Extender Board

The Spectrum is connected to the left hand side of the Backplane board. I added a jumper in the top left to select internal or external power. The mini psu is a TRACO unit, the same as is commonly used in Spectrum refurbishments to replace the 7805. The power socket is a standard barrel with center as positive (reversed to the original Spectrum PSU!).

Why version 2.00? Well, in my haste to get the boards fabricated the first time around, I made a critical mistake. I had got the Spectrum edge connector inverted. This meant that the pass through connections were also inverted! I managed to fry my ZX-HD interface. Hence my rather bad pun as the title. But, a very valuable lesson was learned. Check, check and check again!

The new version is in production and, hopefully, with the right connections! I will double and triple check before connection this time. Once I have proved the design and tested it thoroughly, I will publish the design files on the project page.

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