National Semiconductor 4510 Mathematician

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.

The brown and tan color scheme is very 70s. I think they’d have used wood grain print adhesive vinyl if they could have.

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.

This model isn’t programmable although they made a version that was called the Mathematician PR. Those are a little bit more rare but their programmability is so limited that I didn’t want to deal with finding a nice one at a price I wanted to pay. I also know that personally I do not use the programmability of much nicer calculators I already have so it wasn’t something I’d use anyhow.

What makes this model stand out is its RPN entry method. If you’re not familiar with RPN, there are some great introductions online. I tried to explain it recently and was told that it sounded insane. You get used to it! It starts to make sense… eventually.

This model’s main downside is that it doesn’t do scientific notation, so the range is limited. Some of the math I do most often is around calculating values for circuit components. They are specified in orders of one thousand units. So for example, resistors are commonly available in units of ohms, kilo ohms, and mega ohms. This means you do a lot of math with numbers involving 10^3 and 10^6. Capacitors are similar but much smaller units. You often deal with pico farads – that’s 10^-12. So I’ll have to keep track of the exponents myself when doing those kinds of calculations.

The NatSemi Mathematician is delightfully slow for some operations. For example computing a logarithm of a number is slow enough that the calculator displays an animation of sorts to show that it is “thinking”.

Computing the natural logarithm of pi takes long enough for you to wonder when you’d ever want to know such a value.

I don’t know how much I’ll use this addition to my collection. If I leave it where I can see it, I’ll use it occasionally if only as a muse for an earlier time in computing history.

Book recommendation: Turing’s Cathedral by George Dyson

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.

The cover of the book recalls a punch card.

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.

I’m not going to lie: there are a lot of “white men in ties” involved.

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.

Z80 Single Board Computer

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.

Kaypro BIOS

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.

My CPU card came with a BIOS that isn’t mentioned online – a Phoenix 2.03L. Here is the 8k ROM image.