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Episode 183 of The Gadget Man is out, and it’s about a calculator. Not just any calculator. Mine. I built it, every key, every wire and every beep.
It’s called the Gadio MG-880. It started with a pocket calculator from 1980 and ended on my workbench with a soldering iron, a 3D printer and rather more diodes than any sane person needs. This episode is the story of how it got from one to the other.
The calculator that played Invaders
In 1980, Casio made a pocket calculator called the MG-880. On paper it did sums. In practice it played Invaders. Numbers marched in from the right of the display, and you shot them down with the decimal point and the plus key.
It also had a melody mode, which turned the number keys into a tiny, slightly out-of-tune keyboard. If you were at school in the early eighties, you either had one or sat next to someone who did.
More than forty years later, I decided to build my own. The name is close enough to be a tribute and different enough to keep the lawyers asleep.
In this episode
The episode runs to about 8½ minutes. Here’s where to find each part:
| Time | What you’ll hear |
|---|---|
| 0:00 | The theme, and the sound of the calculator switching on |
| 0:44 | The inspiration: the 1980 Casio MG-880 |
| 1:32 | The brief: 25 clacky mechanical keys, a red LED display and a Raspberry Pi Pico for a brain |
| 2:22 | Wiring it up: a 5 × 5 key grid, 25 hand-soldered diodes, and the first power-up where every column was the wrong way round |
| 3:40 | The software: exact decimals, VAT keys, hex mode, and Invaders on VAT+ three times |
| 4:46 | Getting the sound right: taking a real MG-880’s beeps apart, note by note |
| 5:56 | The case: two 3D-printed parts, an inscription printed into the base, and rubber feet |
| 6:56 | Version 2: a proper printed circuit board |
| 7:47 | Sign-off, and a tune |
What it does now
The trouble with a calculator you can reprogram is that you keep reprogramming it. Since recording the episode, it has picked up a few more tricks. Here’s the full list:
- Sums done properly. Exact decimals, so 0.1 plus 0.2 comes out as 0.3. You’d be surprised how many computers get that wrong.
- VAT keys. VAT+ adds 20%, VAT− takes it off, and they work in the middle of a sum.
- Currency mode. New since the recording. Everything is rounded to the penny, with halves rounded up, as a till would do it.
- Hex and binary. Hex mode was in the episode. Binary mode is new, for anyone who likes their numbers in ones and noughts.
- Number pad. Plug it into a computer and it becomes a USB number pad.
- Melody mode. Seven built-in tunes, tuned 3% sharp like the original. Tune 7 is new: it’s the Gadget Man theme from this episode.
- Invaders. Press VAT+ three times. The high score survives being switched off, which is more than can be said for my concentration.
- A welcome. It now says HELL0 when you switch it on. Every gadget deserves good manners.
Listen
Listen out for the sound effects. The episode opens and closes with the calculator itself: the key click, the eight red digits ticking over, and Ode to Joy played in melody mode. Every beep is a square wave, measured from a real MG-880.
The theme tune is new for this episode too. It’s made from the same beeps, so it sounds like it was played on a calculator, because it more or less was. It’s also tune 7 on the Gadio, if you’d rather hear it on the real thing.
What’s next
Version 2 is on its way, with a proper printed circuit board instead of a nest of hand-soldered wire. When the boards land on my doormat, you’ll hear about it.
If you still have an original MG-880 in a drawer somewhere, let me know in the comments. I’d like to hear it.
Thanks for listening.
Matt Porter, The Gadget Man
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