-

Retro Challenge 2024/10 Prize

2024 marks the 10 year anniversary since I entered the Retro Challenge in… hmmm… let me see now… that’ll be… 2014! Yes, I remember it well, because Retro Challenge 2014 had a catchy hashtag on Twitter, something like #RC2014.

Well, the good folks behind Retro Challenge approached me and asked if I would consider donating a prize for this years event. There were no prizes back in my day, it was all about likes and subs, and inadvertently starting a new career back then. But, hey, I understand that people like prizes, so I said yes. I said I would like to offer an RC2014 Classic II kit to the winner of the RC2014 category

After thinking about it for a little while, I figured I could come up with something a little bit more special. But before I reveal what that is, and before you skip to the bottom of this post for a sneak peek, I wonder if I should explain what Retro Challenge is. Well, it is a challenge revolving retro computers. The challenge is self-set, and you can do pretty much whatever interests you if it involves a retro computer, and you blog about it to share your knowledge and inspire others. Maybe you want to right software for your old Dragon 32, or get that VIC20 cleaned up, recapped and retrobrited, or scan in the original PDP manuals and upload them to the Internet Archive.

Back in 2013 I had built a Z80 computer on a breadboard that ran BASIC. The challenge I set myself for Retro Challenge 2014 was to make my name appear in lights. More specifically I was going to write Z80 code to do it, using a Z80 computer which I also had to design. You can read more about it here https://rc2014.co.uk/653/retro-challenge-2014/

Part of the challenge was to get the PCBs designed and manufactured. I used OSHPark which meant I had 3 of each board. Luckily the designs worked and no serious modifications were needed (although a hammer was required to fit the header pins). You can read about the boards arriving here https://rc2014.co.uk/791/retro-challenge-pcbs-arrived-and-built/

Of the three sets of PCBs I had made, one set was used to build my original RC2014. Obviously. Another set was traded with John Fletcher for an original unpopulated Jupiter Ace PCB (See https://sowen.com/995/ace-adventures-on-jupiter/), and the feedback from that made me wonder if I should get some more made in case anybody else wanted to build their own RC2014.

So, what about the third set? It could be yours!

That’s right. In addition to the RC2014 Classic II kit, I will be giving away the final set of the original RC2014 PCBs to the lucky winner. Well, the original 32k RAM, Pageable ROM, Serial I/O and clock/reset module. The CPU module is a later one which the PCB manufacturer screwed up and didn’t put the silkscreen on the back! And I will throw in an original Digital I/O PCB too. As well as some stripboard.

Everything needed to complete the build is part of the Classic II kit. So when you receive your prize, you will need to decide if you want to build it as a Classic II, or go old school and make the most authentic RC2014 there is.

Not sure if I should put some legal disclaimer here or whatever. The winner will be chosen by the Retro Challenge organisers. I will post out the Classic II kit along with the original RC2014 PCBs mentioned above to the winner within a month of the winner being announced. This includes free international shipping if you are outside of the UK. No cash alternative is offered. Neither myself or the organisers of Retro Challenge can be held liable if you end up starting a new career based on your competition entry.

-

Etch-a-sketchy

In July 2024 I was exhibiting at Liverpool Makefest again. This is a fantastic family friendly makers event that is open to the public for free. It has always been a great place to show off the various RC2014 kits as well as have something interactive that can keep people entertained.

Normally I have a machine set up running Snake, but this year I was about to launch the Dual Paddle Analogue Module, so I wondered about making something with that. The idea of an Etch-a-sketch came up, and coupled with a NeoPixel Matrix Module I figured this would be a nice self contained demo unit.

I could handle the electronics and the physical build, but I reached out to Shiela at Peacock Media to see if she could help on the software side. As both the Dual Paddle Analogue Module and the NeoPixel Matrix Module were Shielas design she jumped at the idea. it was only 5 days before the event though, so we needed to move quick.

There were some important design considerations. Firstly, it had to be robust. One thing about the audience at Liverpool Makefest is there are quite a few kids and they are not always gentle with the exhibits. It also needs to be intuitive. If people need to read instructions, or things don’t give a satisfying output in the first few seconds they you have lost them. On top of that, it should really be self contained to the point where there is no need for a monitor or keyboard, and it just runs as soon as power is applied.

The first thing I needed to work out was the control mechanism. Two potentiometers, obviously, for X and Y, but how are they going to me mounted. I ran through some gamepad type prototypes but things weren’t quite feeling right. Then I noticed a couple of Pot Noodle pots sitting on my desk. These tapered plastic pots are great for pencil pots or other storage, and they stack really nicely. Two stacked together actually turn really nicely and feel good. But could a Pot Noodle pot house a pot? The Pot Noodle was launched at the same time as the Z80, so it seems like destiny, right?

Off to the laser cutter to knock up a prototype. This consisted of a flat square plate with 3.5mm holes in the corners, and another matching plate that had a 100mm hole. This hole was slightly smaller than the brim of the pot, so when screwed down it holds the pot really really tightly to the base. With another pot on top it rotates really well. Putting 10mm standoffs and another pate with 100mm hole in it still allows it to rotate and it prevents the top pot from coming off.

fixing a 10k linear pot to the lower pot was easy enough. I used these lovely vintage RS pots that have a D-shaft

However, fixing the top pot to the shaft was a challenge. Making a D-hole in the top didn’t sound robust, so I decided to 3D print a couple of parameterised knobs in OpenSCAD. I could then glue these inside the top of top pot.

Dear reader, let me share one thing I now know about gluing PP (Polypropylene) plastic that the pots are made of PLA (polylactide) the 3D print it made of – you cannot! There isn’t a glue or solvent that will work. Trust me, I tried many many things.

However, mechanical fasteners (M3 nuts and bolts) do work! The image above shows some holes drilled in the 3D part. Similar holes were drilled in the pots and they were bolted together. Rugged, child-proof and even repairable if needed!

This could now sit on the D-shaft of the pot, and kept from being removed by the top plate.

Next the question about additional controls. Whilst the original Etch-a-sketch was monochrome, the NeoPixel display didn’t have this limitation. There are a few ways to add a digital button to an RC2014, but when there is already an analogue module plugged in, it would be nice to use that.

To achieve two buttons of input, a 1k resistor was added to the negative side of the pot and a switch on the wiper going to ground. In normal use the 8 bit value from the variable resistor will only go down as low as 23, and as high as 255. When the switch is pushed the value is 0. So the software only needs to map approximately 25-255 to the 8×8 display, and anything less than 10 can be treated as a button press. With two pots, this allows 2 buttons, one for to cycle the colour, the other to clear the screen.

Note that it is tempting to put a 1k resistor and another switch going to the 5v line. This will give an extra two buttons, which would be great. However, if both buttons are pushed at the same time it will be shorting 5v and ground. This is a Bad Thing™ and certainly not something you want on a public facing exhibit. Even with a “do not push both buttons at the same time” sign!

A couple of arcade buttons worked great for this, although a label was put on as an afterthought as they weren’t quite as intuitive as hoped.

Shielas software worked great! Burning this on to ROM meant that it just ran on startup without any faffing at all. And with a t-shaped frame that housed the two pots, the buttons, and an RC2014 Mini with NeoPixel Module as well as the Dual Paddle Analogue Module it was a really nice self contained unit.

Things aren’t quite so neat underneath as the wiring for the pots and switches are all routed to a prototype board held together with Kapton tape. But nobody ever looks underneath, right?

How did it go? Great! As always, Liverpool Makefest was a great day out. The folks in Liverpool seemed to instinctively get it straight away. Some people spent a while creating their own Mona Lisa, and others tried teamwork with one person controlling the X axis and the other controlling the Y axis. Nothing broke down or needed restarting and it is all ready for the next event. If anything, the only failing was that it worked too well that nobody particularly asked how it was working, so I didn’t get to talk about the analogue module too much. But at least I got a blog post out of it :-)

The Dual Paddle Analogue Module and the NeoPixel Module 8×8 Matrix are available now on z80kits.com

-

Jig-Ulator

Sometimes an RC2014 has just one job. This one is to go Beep Whoop, Beep Beep Whoop, Beep Beep Beep Whoop! whenever a working Why Em-Ulator Sound Module PCB is put on the jig.

Jig-Ulator

Before we get to that, though, lets go back to the start and consider the Why Em-Ulator Sound Module. This is supplied to RC2014 Towers with the surface mount components assembled and the PCBs panelised. The panelisation is needed so that they will go through the assembly process at the fab house. So the first thing to do is remove the rails and separate the pair of boards.

Pairs of PCBs with rails attached to the side
De-panelised PCBs in front of a wooden box with a slot cut in it and half full of PCB offcuts

Removing the rails is made easy with a slot cut in to a wooden box. The rails are put in to the slot and a quick bend up and down detaches them from the main PCB. The discarded rails are then collected in the box. Breaking the two PCBs apart is also a simple process.

Next the micro controller needs to be programmed. The PCB has a TC2030 Tag Connect compatible programming header next to the micro controller. The programming cable has spring loaded pogo pins and some locating pins that protrude through the board. To accommodate this, a small jig (Jiglett) is used.

Laser cut perspex jig with an RC2014 module shaped cut out along with finger holes to remove the PCB and a hole below the programming pads for the locator pins to go
Programming lead being held in for the 3 seconds it takes to program the micro controller
Fully programmed module ready to be removed and tested

The programmer is a stand alone device which has the flash hex file, eprom hex file and fuse settings for the default Why Em-Ulator settings (YM2149 at 1.7734MHz). Other settings can be programmed manually from a laptop.

For peace of mind that the firmware has been programmed successfully, and that the assembly process was correct, it needs to be tested. This is where the Jig-Ulator comes in.

At the heart of the Jig-Ulator is an RC2014 Micro. This sits in a Backplane 5 with 3 sockets fitted. One of these sockets has a Digital I/O Module for visual feedback and the other has a Rev 5 YM2149 Sound Module with an AY-3-8910 to AY-3-8912 adapter. This adapter carries all the signals (Power, 8 data lines, Reset, BC1 and BDIR) that the Why Em-Ulator needs to operate, as well as the return path for the sound from Channel A, Channel B and Channel C. The sound module is plugged in to a speaker for audio feedback.

At the front of the Jig-Ulator is a bed of nails test jig made from laser cut Perspex and pogo pins. The Perspex holds the pogo pins in place, and the upper layers have an alignment cutout so that the module under test will line up perfectly with the pins. A little bit of pressure ensures that all signals make good contact.

The RC2014 Micro has some very simple test code in ROM that runs on startup and continues indefinitely. This code isn’t elegant. Nor is it particularly efficient. And it certainly isn’t an example of how to write good Z80 assembly code. However, it has one job, test the module, and it does that well.

All of this only takes up a couple hundred bytes of the 8k ROM. It can surely be optimised to take up less space. Alternatively, the calls can be unrolled to take up more space but without needing any RAM for the stack.

            .ORG    $0000 
REG         EQU     $D8 
DAT         EQU     $D0 
START:               
            NOP      
            NOP      
            DI       ; disable interrupts
            LD      hl,$9000 
            LD      sp,hl ; set up stack
            NOP      
;set mixer reg to enable channel A
            LD      a,7 
            OUT     REG,a 
            LD      a,62 
            OUT     DAT,a 
            LD      a,15 
            OUT     0,a ; set DIO lights right

;set channel A to max volume
            LD      a,8 
            OUT     REG,a 
            LD      a,15 
            OUT     DAT,a 

;output 2 note to channel A
            LD      a,0 
            OUT     REG,a 
            LD      a,128 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,255 ;high note
            OUT     DAT,a 
            CALL    delay 

;decremental tone
            LD      a,0 
            OUT     REG,a 
            LD      b,255 
            CALL    ALOOP 

;set mixer reg to enable channel B
            LD      a,7 
            OUT     REG,a 
            LD      a,61 
            OUT     DAT,a 
            LD      a,$F0 
            OUT     0,a ; set DIO lights left

;set channel B to max volume
            LD      a,9 
            OUT     REG,a 
            LD      a,15 
            OUT     DAT,a 

;output 4 note to channel B
            LD      a,2 
            OUT     REG,a 
            LD      a,255 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,128 ;high note
            OUT     DAT,a 
            CALL    delay 
            LD      a,255 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,128 ;high note
            OUT     DAT,a 
;decremental tone
            LD      a,2 
            OUT     REG,a 
            LD      b,255 
            CALL    ALOOP 

;set mixer reg to enable channel C
            LD      a,7 
            OUT     REG,a 
            LD      a,59 
            OUT     DAT,a 
            LD      a,60 
            OUT     0,a ; set DIO lights middle

;set channel C to max volume
            LD      a,10 
            OUT     REG,a 
            LD      a,15 
            OUT     DAT,a 

;output 6 note to channel C
            LD      a,4 
            OUT     REG,a 
            LD      a,128 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,255 ;high note
            OUT     DAT,a 
            CALL    delay 
            LD      a,128 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,255 ;high note
            OUT     DAT,a 
            CALL    delay 
            LD      a,128 ;low note
            OUT     DAT,a 
            CALL    delay 
            LD      a,255 ;high note
            OUT     DAT,a 
;decremental tone
            LD      a,4 
            OUT     REG,a 
            LD      b,255 
            CALL    ALOOP 


;turn sound off
            LD      a,7 
            OUT     REG,a 
            LD      a,63 
            OUT     DAT,a 
            LD      a,0 
            OUT     0,a 
            CALL    DELAY ; wait....
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            CALL    DELAY 
            JP      START ; and start all over again


            EI       ; enable interrupts
            RET      ; which will never get to. But helpful for debugging RAM based versions of the code
SHORTDELAY:          
            PUSH    hl 
            PUSH    af 
            LD      hl,1000 
            JP      DELLOOP 

DELAY:               
            PUSH    hl 
            PUSH    af 
            LD      hl,$ffff 
DELLOOP:             
            DEC     l 
            JP      nz,DELLOOP 
            DEC     h 
            JP      nz,DELLOOP 
            POP     af 
            POP     hl 
            RET      

ALOOP:               
            LD      a,b 
            OUT     DAT,a 
            CALL    SHORTDELAY 
            DEC     b 
            JP      nz,ALOOP 
            RET

After starting up, interrupts are disabled and a stack area is defined. Then it makes a Beep-Boob on channel A, whilst turning on the right 4 LEDs on the DIO module, then plays a Whoop noise. It then does this again on Channel B, but with a Beep-Boop-Beep-Boop and illuminating the left 4 LEDs. And finally, it does this again on Channel C, but with a Beep-Boop-Beep-Boop-Beep-Boop and the middle 4 LEDs. Slight pause and back to the start.

The whole thing only takes a few seconds to confirm that everything is working as it should.

-

Retro Challenge 10/2016 – Still a work in progress

So, who remembers my entry for Retro Challenge in January?  It was quite devoid of effort and results I think you’ll agree.

Well, this time around, I’ve taken that theme and pushed it even further!  Even less effort and much less result.

Since January, I have had a few opportunities to carry on with the ZX81 Module.  Because I wanted this to be a Retro Challenge project, I deliberately avoided doing any work on it, so I could save it all for October.  Well, October started and I was overwhelmed with non-Retro Challenge stuff.  But after a couple of weeks, I had a spare afternoon, and decided to dedicate this to the ZX81 Module!

So, I dug out the PCBs I had manufactured in January and fired up the soldering iron;

retrochallenge10-2016_1

Time to wrack my brains and work out what my plans had been 9 months earlier.  I had failed to put any component values on the PCB, or even my Kicad schematics, so had to rifle through original ZX81 schematics to work out what these should be.

Now I knew what components I needed, it quickly dawned on me that I didn’t have very many of these at all.  This didn’t deter me though.  I fitted everything I had; IC socket, pin headers, some resistors and some transistors that may or may not be compatible;

retrochallenge10-2016_2

And that’s about it.  I have ordered the rest of the parts now, but not had an opportunity to fit them.  yet.

One thing I have learned from this experience though, is that if I get any opportunity or urge to work on this, then I will seize it.  Not wait until the next Retro Challenge.  If I’d done work on this months ago when I had the chance, then this would more likely be a trouble shooting / tweaking / developing challenge.

One other good thing that has come out of this though, is that when I started this in January, I had a few design changes or additions required for the RC2014 for it to work.  The Backplane 8 has the ability to add resistors between the CPU and the RAM.  The Universal Micro Keyboard has the right connections to work with a real ZX81 or this ZX81 Module (including diodes).  The CPU Module also now has BUSRQ, WAIT, NMI and WAIT pins broken out which is required for this.  These changes should all make things much easier.

Despite my poor efforts this time around, I have thoroughly enjoyed seeing what everybody else has achieved with their Retro Challenge.  Good work everybody else!

-

Retro Challenge 2016 – My Dog Ate My Homework

So, all the way back in deepest darkest December, I announced I would enter the Retro Challenge 2016 competition that ran throughout January.  Those of you that followed by blog or Twitter account when I did this in 2014 will know that I blogged and Tweeted relentlessly for the whole month, but, this time around, almost nothing.  Obviously, I’m keeping some secret about an amazing breakthrough or something, right?  Well, truth is, I’ve done almost nothing.

Things started well, and on 1st January, I designed a new backplane for the RC2014.  Although I hadn’t studied the circuit diagrams for the ZX81, Jupiter Ace or ZX Spectrum yet, I knew that there were resistiors between the Z80 CPU and other devices.  The stripboard backplane I’d been using had served me well, but it was time to progress to a better solution, and one that could be adapted better to my needs.  Knowing that PCB delivery times could be against me, I thought it best to crack on and get this  ordered.

Screenshot from 2016-01-31 16:01:00

The basic circuit is very very simple – however, I wanted to get this just right, not only for Retro Challenge 2016, but for other possible RC2014 uses.  Essentially, there are 8 40 way connectors that are linked straight through – however, the data lines and address lines for the leftmost 2 connectors and rightmost 2 connectors are separated by a pair of pads.  These can either be shorted together for up to 8 commoned connectors, or have resistors soldered across them.  I also added a power connector and the option of either running 5v directly in to the board, or regulating a higher voltage down via a LM7805.

(more…)

-

HDMI and USB Keyboard Support

So, the RC2014 is a great little computer.  We all know that.  However, to communicate with it, it is easiest to use the serial port and hook it up to a laptop or desktop PC.  This makes detracts from the fact that it is small, portable and cheap as well as missing the point of running code on such a basic computer.  So I’ve been looking for a solution to this.

Back when this was still running on a breadboard, I hooked up an Atmel ‘328 that was connected to a keyboard and 4 x 20 LCD display.  It communicated with the RC2014 over the serial port and kind of worked ok, although 4 lines was very restrictive and the Atmel couldn’t really keep the screen running and listening at the same time.   I have thought about using a ‘328 to drive a composite output, or maybe some kind of bigger LCD panel, but nothing really struck me as just right.

That is, until the kind people at Raspberry Pi released a cheap multifunction interface device a couple of weeks ago!

2015-12-18 22.13.44

(more…)

-

Retro Challenge January 2016 – Preamble

So, you may well remember that I entered Retro Challenge 18 months ago, and what a fun crazy busy time that was!  Well, the January Retro Challenge competition is about to kick off in just over 2 weeks.

If you’re not familiar with Retro Challenge, shame on you!  But you can de-shame yourself by heading over to http://www.retrochallenge.org/ and seeing what it’s all about.  Essentially, it’s a month long bi-annual competition where the entrants set themselves a goal based around old school computing and blog, tweet and share their experiences.  The goals are pretty loose, as long as they are based on something from last centuary (modern emulators of old kit is fine).

The challenge I set myself was to take a breadboard based Z80 computer and bring it to life in modular PCB form in such a way that I could spell out my name on.  Have a look back through my blog to see how I did.  Spoiler —->

IMG_20140730_205950

(more…)

-

RC2014 SD Bootloader Update

Just a quick update to about the SD Bootloader I designed a few posts ago.  Well, the PCBs have arrived and last week I took a soldering iron to one of them and gave it a quick test

One side of the board is effectively an Arduino, so without plugging it in to the RC2014, I connected up an FTDI lead and uploaded the Arduino Blink sketch.  A quick check with a multimeter and one of the pins was altenating between 5v and 0v.  So far, all good! (more…)

-

RC2014 Bootloader for SD Cards

So, the RC2014 is great.  I can run Microsoft BASIC and program it from there, and as long as I am using a terminal emulator, I can copy & paste to save and load programs.  Alternatively, I can write Z80 code using an online compiler then download it, copy it to USB stick, move it to my old Windows 2000 laptop (which has a parallel port) so I can burn it on to EPROM to see if it works, make adjustments and repeat with another EPROM.

I will be the first to admit, however, that this is probably not the most efficient workflow.  Not to mention the time and effort involved in wiping the limited stock of aged EPROMS.

So, I am in the process of designing an SD Card based bootloader.

i (2)

(more…)

-

RC2014 with ZX Printer interface

My original plan had never been to design and build my own computer.  I had, however, planned to build a clone of the Sinclair ZX80, which has been on my bucket list of things to own for year, and which I had found plans for online.  Whilst collecting the parts and reading up on simple Z80 computers I got kind of sidetracked and ended up with the RC2014.

The print out shown was what was left from the last time this was connected to a ZX Spectrum!

The heart of the RC2014 is a Zilog Z80 CPU, which is the same one that Sinclair used in the ZX80, ZX81, ZX Spectrum and Z88.  If the ZX81 and ZX Spectrum can run a ZX Printer, then surely it follows that the RC2014 will be able to too?

(more…)

page 1 of 3