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.
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.
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.
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.
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.