Digirule2 review

In the earliest days of computing, ‘programming’ was a very physical job, involving the connecting and disconnecting of thousands of individual wires. Later, these wires were replaced with toggle switches, and later still by offline storage devices like punch-cards, paper tape, magnetic tapes, and eventually disks.

In the years since the launch of the Altair 8800, an imposing desktop computer which was programmed exclusively through front-mounted toggle switches, the focus of computing has been to distance the user from the lowest level of how a computer works – the zeroes and ones of binary code. Without that distance, modern computing – where memory is measured in the billions of bits and storage well into the trillions – would simply be too much to manage.

That’s not to say you can’t go back to the good old days of bit-by-bit programming if you want to, though. The Brad’s Projects Digirule2 is an implementation of just such a low-level system: a very basic 8-bit computer not a million miles away from an Altair 8800, but instead of taking up a chunk of desk space, it slips neatly into a pocket.

••Drawing a line••
The Digirule2, in fact, is presented in the shape of a ruler, complete with inches and millimetres marked in binary on its longest edges – though the fact that these markings start proud of the edge of the device means it’s not the clearest ruler to use.
Measuring isn’t the Digirule2’s main function, though. Despite its surprising size, it’s a fully-functional microcomputer – complete with its own built-in display, taking the form of a series of LEDs to the device’s left-hand side.

Inserting a button-cell battery – which only clips into place, so it’s not something to give to young children unsupervised – and flicking the power switch springs the Digirule2 into life. Its LEDs will light to show that it’s ready to receive input, which you do by inserting binary bits – the zeroes and ones that are the only things a binary computer understands – into memory using the push-button switches. Each switch corresponds to one bit of an 8-byte memory address; a program can take up 256 bytes of memory in total, and there are eight slots for you to save programs into for later recall.

That’s not a lot of memory: Minecraft, for instance, takes up a minimum of 180MB – 188,743,680 bytes – which gives you an idea of just how limited the resources of early personal computers were.


With limited resources, you need unlimited ingenuity. Using the 33 instructions printed on the back of the Digirule2, and repeated with full explanations and usage examples in the downloadable manual, it’s possible to write some surprisingly functional programs. The Digirule2 comes with a selection preloaded, including a reaction-testing game called Kill the Bit, and a persistence of vision (POV) trick which draws smiley faces as you wave it around the air in a darkened room.

The Digirule2 isn’t likely to replace a desktop, laptop, or Raspberry Pi anytime soon, but it’s not trying to. The device exists as a means of easily playing around with low-level computing concepts, deliberately using limited specifications to make the user think about how something can be achieved in as little space as possible.

••Getting Started••
It’s here that the Digirule2 excels. The downloadable documentation is extremely detailed, and an update released earlier this year has corrected some minor typographical errors and other small mistakes. Better still, everything is open source: the downloads included on the Brad’s Projects website include not only the manual, a spreadsheet which allows you to convert your programs into the binary code you need to enter on the device, and other tools and utilities, but the design files and source code for the Digirule2. With these, it’s possible to build your own – though soldering the small surface-mount components is tricky without practice.

With its low cost, accessibility, and quality documentation, it’s easy to see the Digirule2 finding a place in classrooms throughout the world. Its use for education comes with a caveat, however: while the Digirule2 teaches the core concepts well, its custom instruction set doesn’t directly translate to anything in the realm of modern computing – meaning that anyone wanting to move on to a device with a bit more power, up to and including a modern PC, will need to learn a whole new instruction set or abandon low-level programming in favour of a high-level platform-agnostic language like Python, or C.
Outside education, the Digirule2 still has value. Its small size, and ability to function as a ruler for drawing straight lines or measuring them, means it’s the perfect desk toy, hiding away until you feel the need to impress someone with the preprogrammed Larson scanner example, Police Flasher animation, Target Practice game, or software of your own devising.

At just shy of $16 (around £12, excluding VAT), the Digirule2 is worth the cost of ownership just as a curiosity, but if you use it for education, either to teach yourself or to teach others the concepts behind low-level computing, it becomes an absolute bargain.

Digirule2 From $15.95 bradsprojects.com

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