Tuesday, 25 April 2017

ZX Spectrum Project - Part 1

The project has started off quite simple. I removed the case and the RF modulator and gave myself a composite output. I then removed the 7805 and the coil and connected a USB-B socket to the board to take a 5V input. I am now realising that the graphics memory requires 12V and -5V to power it as all I am now getting on the screen is the flashing bars of doom. I am going to try and replace this memory with a more modern device, preferably a single chip rather than eight.

I am also thinking about what I want to achieve from the board. I am definitely going to be attempting to recreate the Spectrums ULA using a combination of some logic and a microcontroller, this will be challenging but there is enough information about the part out there. I will probably also create a new PCB as the old one uses a lot of one bit memory chips which eat up space where the modern eight bit parts will be much smaller. I think the new PCB will be more than achievable on a dual layer 100mm X 100mm board. I also think that it would be a good idea to integrate two game ports rather than having an edge connector on the back. Also, being able to use a modern keyboard would be a plus as the Spectrums keyboard is horrific.

As I have no plans to use the original keyboard I have removed the connectors and replaced them with pin header which is much easier to connect to.

Parts used so far
- 1 x ZX Spectrum with issue 4b board from 1983
- 1 x USB-B connector
- 1 x Phono RCA connector
- Wire

Pictures from today