After a what can only be described as a very strange year, I find myself working on a project inspired from yesteryear.
The ZX Spectrum from Sinclair Research was the first computer that I owned, getting it 1982. One of the books I bought back then was the Spectrum Hardware Manual by Adrian Dickens. I remember building many of the circuits described in it, both temporary on breadboard and also permanently on Vero board.
Now fast forward to today, December 2020. Inspired by those early days I have designed a couple of PCB’s to make building circuits for ZX Spectrum a little easier than back then.
There’s a quartet of boards: starting with a breadboard PCB, next we have a prototyping board, another more advanced prototyping board with decoding IC’s and finally a bus extender PCB with vertical and horizontal signal expansions.
In the picture above, on the right, we have a Raspberry Pi adapter that allows two Feather modules to be used with the RPi. The RPi’s UART, I2C and SPI are available to be used with the Feather modules. You can mixed things around if you want and have a Feather controller and Feather I/O module setup to offload real-time I/O from the RPi or just have two Feather I/O modules to expand the RPis I/O capability.
Next to the RPi adapter, with have an analogue input module using the popular 8-channel MCP3008 ADC (SPI) chip.
Next to that, we have a couple of 16-channel digital port expanders, based on the MCP23017 (I2C) and MCP23S17 (SPI) chips respectively.
I’ve been a long time fan of the Arduino Nano and before those the Arduino Mini boards. I really like the compact Nano footprint and prefer it to the standard Arduino Due style. When I ran of computing processing power I would swap the Nano’s for the STM32 blue pill boards. So I thought I had a good choice of modules to choose from. But this has changed recently and another module footprint has entered my projects orbit.
The Adafruit Feather modules have been around for a few years and a recent project requirement saw me using their nRF52840 Express module for a Bluetooth Low Energy (BLE) based design. I liked what I saw but couldn’t find a decent prototyping solution, so I designed this prototyping / breadboard to help with getting my Feather module projects started.
The FeatherWing prototyping / breadboard has headers for a Feather module, as well as space for a 400-hole breadboard. Additionally it has PCB positions for 3x tactile switches, 3x LED’s and a FTDI style serial pin-header. Finally, all the Feather module signals are broken out to a double row header located next to the breadboard.
It’s been a while since we published any thing new for the RC2014 architecture.
This is a simple combined ROM and RAM card designed to work with the RC2014 bus. This is an experimenters board. There is no fancy memory paging etc., it’s simple memory architecture was designed to be flexible and allow the user to experiment with other CPU architectures on the RC2014 bus. It was originally designed to work with our 8052 CPU.
enhanced RC2014 bus
Selectable memory* options 8K, 16K or 32K
Board can be used as RAM only or ROM only or both.
Options for nMRD/nMWR or nRD/nWR signals
Option for 27C512 with Hi/Lo ROM (A15) select
IC Decoder 74xx138 using A15/A14/A13 (with extra options for A13 & A14)
8 or 16-bit wide data bus**
moveable memory positions (i.e. ROM can be at top or bottom memory space)
A couple of important notes:
* Both ROM and RAM memories must be the same size.
** see explanation below
The option for either nMRD and nMWR (nRD and nWR or’ed with nMREQ) signals or nRD and nWR only signals when IC3 (74xx32) is fitted or not fitted allows for experimenting with other CPU Read/Write architectures.
Notably, the enhanced RC2014 bus features a 16-bit data bus. The card can use this enhancement by allowing the selection of the high or low 8-bit portion of 16-bit data bus. This allows the user to experiment with 16-bit CPU’s such as 68000 or 8086 when two cards are used together.
I’ve always found application notes to be great places to expand your knowledge and understanding. Microchip have released or rather re-released a handful of power electronics related notes this month:
It’s not very often that I comment on current events but the Coronavirus or COVID-19 or SARS-Cor-19 is too big a world event not to have some views about. As a maker and also a professional (cough) engineer I’ve been intrigued by the maker community’s response to these events. We’ve seen makers use their faculties to make face masks and face shields using 3D printers, sewing machines etc. not for themselves but for their wider local community and their local health professionals to help protect others against the spread of the virus.
There are many makers and maker companies that have been very proactive in this, just naming a few, companies like Adafruit have lead the way and their blog has many posts. Other useful sites I found are:
Maker communities such as Hackaday and Instructables also have many useful posts. As well as the blog entries themselves, the various comment section are full of very interesting points made by reverent professionals, as well as interesting details and suggestions by other interested parties. Below is a short list of some of the other links found:
And finally, its also the call to arms by many governments to their countries biggest or best industrial companies to help eleaviate their medical equipment shortages. The mainstream media have been quick to jump on these stories of Formula 1 teams, big defence and big consumer companies banding together to rapidily design and manufacture the much needed medical equipments. Others have asked why their countries are not doing the same or enacting war time or emergency powers to allow manufactures to quickly add their manufacturing might to the effort.