What should this retro computer do and how should it benefit me on a daily basis? That’s the question! Well…I will look at porting a version of Basic to the system. That will provide me with a programming language that I will be able to use to develop the application. What if the system also monitors the temperature, humidity, solar radiation and rainfall from the environment in and around my workshop?

By designing the system to be ultra low power while operating, it should have the ability to go asleep when the workshop is powered down, only waking up at specific intervals, to record the necessary signals, save the data and go back to sleep.

Power requirements should be very simple – a small solar panel charging a battery that the unit will run off.

It would be nice to have some form of display. Display controllers drain power so it will be best to keep the system power consumption as low as possible.

After checking stock, I have found some old HD63x0x micro’s that will form the basis for this project. These micro’s have some onboard peripherals that will help when trying to connect to the outside world. The most important component that I see is the on-board UART, which will allow for RS232 communications to a PC.

While it would be fantastic to have a system that records this information, what if I want the system to do something totally different in the future – having one PCB which is the computer core and another which is the interface – some form of stackable system like the PC104 systems that exists?  I will start on making the SBC, (Single Board Computer) and then I’ll focus on the interface board later. At the same time I’ll need to think about how the interface board will work and how to connect other interface boards…

Having a separate interface board is making me think about having other boards attached as well, like a floppy drive controller, to let the system connect to a 3.5″ floppy drive (just because I have a few of them lying about in the workshop). What about a video display board? I know that this wouldn’t fit into my thoughts about low power, but if the system is modular, I could make up a system that is low power for the data logging solution and another system as the desktop retro computer (all from the same technology). Then I will look to see if I can get them to talk to each other, to my PC, or my Mac.

Have been thinking over the idea of building a retro computer that uses technology from my early computer years. Nowadays I design systems based on modern micro controllers, but the old micro’s hold some nostalgia for me.

So what to build and how should I build it?

My first thought was to use the 6502 processor or the Z80 processor, but so many other bloggers and Youtube channels have built retro computers around these CPU’s. I was thinking about one of my favourite computers from the late 80’s – the Epson HX-20, the first true portable computer – battery powered that lasted up to 40 hours, yes, 40 hours. It’s mad to think that almost 30 years ago we got 40hrs on a computer and todays laptops find it hard to get a day.

This little machine has a built in printer which has been very handy for printing results in the field. It also has a micro-cassette drive, which allows the loading and saving of both programs and data. I used one of these machines between 1985 and 1993, while working in my Dad’s company. We provided loggers to companies and semi-state authorities.

If I decided to build such a device, what could I use it for? Could I make it in such a way that it would be functional and able to complete some meaningful tasks for me? Of course I could use an Arduino or a raspberry Pi, but where would the retro nostalgia be in that.

The Epson HX-20 uses an Hitachi low power CMOS CPU – the HD6301. This chip is a CMOS version of the Motorola 6800 family of IC’s, so maybe this could be the starting point?…

This project will be a work in progress, as I trial different ideas to find a solution that ticks the boxes that I’m interested in. A bit self indulgent I know, but hey, its my project.

My plan is to build something that’s as reliable as an HX-20 but actually better than one?