I was getting bent out of shape that I needed to somehow reconstruct the system clock out of the data stored inside a delay line. But fooling around with an old discrete delay line simulation in a circuit simulator by replacing the giant stack of flip flops with a proper length delay line shows that I don’t need to be too concerned
As long as
The delay line stays a constant delay length in terms of time (dubious)
The system clock stays a constant speed (actually very easy because amazingly stable crystal oscillators are trivial nowadays)
Delay lines varying in time is
Highly probable with any sort of rotating media (magnetic drums, etc)
Less likely for “solid state” delay lines such as acoustic torsion delay wire.
Unknown for any other technology (tape loops?)
For rotating media or tape loops, it would probably be good to assume they require a second timing track. It’s somewhat of a “waste” of media density, but you should only need one per media – so one track on a drum or one track on the tape. You can have as many other tracks as you can cram on there.
For the more stable media, where the main drift is due to temperature, there could be some type of calibration mode where a signal is put into the delay line and then compared to the current clock speed. The clock speed could then be adjusted to match. This could even be automatic – perhaps something you would perform once on startup, and then once again when the machine is up to operating temperature. Of course any thing that is temperature dependent is probably best handled by installing a heater and keeping it at a steady 100degF (or whatever) no matter what.
I have a small collection of vintage calculators that I stumbled into collecting. I found one at a garage sale, and then one was given to me, then I found a neat one on eBay for a good price… Before I knew it, I was a calculator collector.
I actually use most of them despite having a great calculator app on my phone because I prefer their physical interfaces. I have one on each desk and one in my bag so I don’t have to go searching. I don’t have that many bags and desks though so there is also a small stash in a drawer.
My latest addition is a National Semiconductor 4510 Mathematician from the mid 70s. It has an 8 digit red LED display and runs on a 9 volt battery. There is a jack on the top edge for connecting a wall supply if you’ve got a lot of math to do.
It is in great condition and the seller even included a brand new battery. It is one of the lesser RPN calculators of the 70s and not expensive. Like most of my collection, is not valuable but it is uncommon.
If you’re interested in the early history of computing, check out Turing’s Cathedral by George Dyson. It covers an interesting middle phase between the original electronic digital computers and the wide commercialization of computers in the late 50s.
Specifically it examines the people and development around “the IAS machine” at the Institute for Advanced Study at Princeton. Big and not as big names make an appearance, and it is a detailed account of the forces at play: academia, industrial, military, and political.
The design of the “IAS machine” was the pattern for dozens of machines around the world. More than one country’s “first computer” was one built using the design developed by the people at IAS. I think of it as the first practical computer – the construction needed to solve a lot of problems that the original electronic computers didn’t need to address because they were just struggling to exist.
It’s been a while since I finished the book, but I do refer to it when I need details of how some design constraint was surmounted. It also includes enough biographical information that I use it to jog my memory of exactly who was who. The world of computing was still small enough that people who contributed to the IAR project show up in other places pretty often.
It’s widely available. It looks like Thriftbooks has it for under $5, so you could get it for free if you’ve got some reward points there.
Because the first assembly language I learned was for my TI graphing calculator, I’ve have a soft spot for the Z80 CPU. It’s a nice 8 bit architecture and widely used in pre-MSDOS machines. The Apple II used a 6502 but more or less all the “business class” machines ran CP/M on a Z80.
It has a 16 bit address bus so it can address 64k of RAM, which is fine for an 8 bit machine. You can do bank switching to get access to more, which is what CP/M does.
I’ve breadboarded some very rudimentary Z80 machines over the years, but the Z80-MBC2 by Just4Fun is a great take on the genre. The twist is that it uses a Atmel AVR as a supervisor/ROM emulator/IO coprocessor of sorts. It makes it very easy to rapidly develop ideas when your IO system is reprogramable!
After assembling and experimenting with one, I decided I wanted the ability to support traditional expansion methods. There is standard DIY-oriented bus format for Z80 systems called RC2014. It is more or less the 40 pins of the Z80 CPU itself spread out in a 1×40 header. So I built an adapter that sockets in-between the CPU and the MBC2, pulling the bus lines out to one side. I used veroboard because its straight-through traces make extending the bus a cinch.
I haven’t had a chance to revisit the project lately, but I plan to. I assembled a composite video card for RC2014 and need to try it out.
I’ve recently gotten back into retro computing in the IBM XT clone genre. I obtained a set of Kaypro PC-compatible boards – a CPU card, a backplane, and a RAM card. I’ve been slowly working with them to build a 8088-based PC of the late 80’s.