This is a copy of the recreation that used to be hosted at http://projectspeccy.com/projects/ with permission from Steve SmithA long time ago, there was a fabulous magazine devoted to the Spectrum called Your Spectrum (Later becoming Your Sinclair). An article about add-ons for the machine was published. The article was illustrated using a Backplane to support a variety of peripherals.
Although the article doesn’t mention the backplane, I always remembered it and thought it was a good idea. This led me to design one for my use.
It took a couple of versions to get the connectors correct! All of the edge connector pins are straight through, meaning that it should be compatible with all Spectrums and, aside from the onboard power supply, also be compatible with other machines that use 28×2 edge connectors (this has not been tested!).
The optional onboard power supply is purely for the peripherals and does not feed into the machine it is connected to. There is a jumper to select whether the peripherals are powered by the connected machine or via the onboard power supply. It is based around a Traco unit that can supply 1.5A of current. It requires at least 6.5v to operate properly but any center positive supply of 6.5v – 12v should be fine. Included is a power LED to indicate external power is being used. There is also a convenient reset switch.
There are two straight-through edge connectors to mount interfaces in the traditional fashion. One on the left-hand edge and one on the rear. The other four connectors can be used with IDC pin headers, sockets, or adaptors. The design files include PCBs for adaptors to convert these to standard edge connectors, albeit vertical. The adaptor board is soldered between the pins of an IDC plug to make up the adaptor.
Although I have found them to be ridiculously expensive, it’s a good idea to put polarising pins in to the IDC socket in the ‘slot’ positions to avoid the adaptor being plugged in the wrong way.
I have carried out the minimum of testing on this board so far and you will notice that there are no buffers included as yet, this may be rectified in the future. It has operated fine with my hardware. So, the design is there to experiment with as is. If you choose to build and use one, it is entirely at your own risk, and no responsibility will be taken for any loss or damage.
All the files necessary for fabricating the Spectrum Backplane v2.00 can be found here https://github.com/lostretrotapes/Sinclair-Spectrum-Backplane