RetroMatic 2000 update 13: knobs!

We’re in the home stretch for the Retro Challenge – it’s supposed to finish on the last day of April, which gives me only 5.5 days left.

Realistically I won’t have everything done by then, so it’s time to re-assess what’s achievable to get a ‘minimum viable product’, and work towards that.

And that means buying the last tranche of components I’ll need – it’s time for some shopping :-)

Since I discovered that buying components direct from China was easy, cheap, and faster than I’d expected, it’s a balancing act of working out if I really need something this week, or if it can wait for 3-4 weeks.  It’s also complicated when a component is so rare that it would cost ten times as much to buy it from the UK!

So with the (slightly artificial) deadline of the Retro Challenge, what do I actually need to get me to the end of the challenge?

All prices quoted included shipping to the UK.  I bought from a mixture of eBay sellers and Aliexpress.

Components ordered from the UK


These are pretty important for the minimum viable product: I’d like to at least be able to build everything into the project case and show everything working (even if it’s still on breadboards inside).

I’ve got two knobs for the two rotary encoders (£5.99 for two), and a pointer for the drive selection switch (£1.69).  All beautifully evocative of the 1980s (or earlier), which is my chosen design aesthetic.


Essential: a rotary switch for the drive selection (the above pointer knob will go on it). 6 position, 2 pole, break-before-make, £3.74:

Nuts and bolts

Essential for fixing all the panel-mount items to the case.  M3 bolts (20mm long), nuts, and washers x 100 for £2.89:

Components ordered from China

Replacement HD9800 video board

As I’ve previously written, I think all my prototyping has broken the i2c input on my HD9800 video converter board.  So I’ve bought another one (I actually ordered it a week ago, so there’s a very small chance it might arrive before the end of the challenge).  £12.87:

Phono (RCA) sockets

I’ll need at least one phono socket for my composite video input.  I think I might end up adding three sockets (for composite/Y, U, V) for future enhancements.

According to its specs, the ZX Spectrum is capable of outputting YUV from its edge connector.  If true, I’d be able to get a video input straight from a Spectrum to my RetroMatic box, which would be pretty awesome!  No-one else has ever written about it though, so I need to do some tests to see if that would really work.

So I bought 10 sockets for £1.38:

USB socket

The USB socket on the Gotek floppy drive emulator will be hidden inside the case, so this extension lead with a panel-mount USB A socket will allow the USB socket to be conveniently placed. £0.81:

Power socket

A panel-mount barrel-style power socket (5.5mm external x 2.1mm internal) for the external power supply  Pack of five for £0.56, so plenty for future projects:

DC-DC power converter

As I wrote in my power audit, these power converter boards are an absolute steal (if they work as described).  They can deliver 1.8A (3A peak) at 1v-17v.  I got ten for £2.46!

Floppy cables and connectors

These 34-pin cables and connectors will enable me to extend the floppy drive socket from the Gotek emulator to outside the project case, and also allow me to modify my Video Genie floppy drive cable to use the USB emulator at the same time as a real drive.

One metre of 34-way cable (£1.42), five male connectors (£4.37), ten female connectors (£2.30).  Hmm, is that evidence of a gender pay-gap?  Those male connectors are expensive, but I couldn’t find any for sale in the UK: it seems that most male floppy connectors are designed for circuit boards, and it’s pretty unusual to find IDC cable-mounted versions.

PCB spacers/stand-offs

Mounting PCBs is a pretty new thing for me (so far I tend to just shove a bread board in a plastic box).  I read loads about different ways of mounting boards, and it seems there are a multitude of ways.

In the end I decided to use some plastic tube spacers in conjunction with the M3 bolts I’ve already ordered.  I’m not sure if it’s optimal, but if ought to do the job.  I got fifty 15mm long M3 (3mm) nylon spacers for £2.49:

Now back to work!