There’s an old joke that there are 10 kinds of people in the world. Those who know binary, those who don’t, and those who didn’t see a base three joke coming. Perhaps [Dmitry Sokolov] heard that joke because he’s built a ternary (base 3) computer. He claims it is the first one to be built in the last 50 years. You can see a video about the device below. There’s also a video of the device with a nixie tube output.
You may not think of it often, but bit is a contraction of binary digit, so a ternary computer doesn’t have those. It has trits. The CPU operates on 3 trit words and uses nothing but multiplexers as building blocks. Instructions use 5 trits, some of which are a two-trit opcode and a 3 trit address of one of the 13 registers. The allure of using ternary, by the way, is that you can represent more numbers in fewer bits — um, trits, rather.
That might seem like an odd number of registers, but using balanced ternary, a 3 trit word can represent numbers from -13 to 13, so it makes sense. Instead of a bit’s 1 and 0 state, a balanced trit has -1, 0, and 1 states. To prevent confusion, [Dmitry] uses the notation N,0, and P when talking about a ternary word. For example, 101 is 10 decimal or P0P in his notation. To represent -10, you simply use NoN, instead.
The multiplexers use an analog switch, the DG403. We’ve talked before about making logic gates out of muxes, but — of course — those were the binary kind. However, we aren’t too sure this is really the first of its kind in 50 years since we remember a Hackaday Prize entry that was similar. In fact, the designer gave a talk about her CPU at last year’s Hackaday Superconference. Still, this is an impressive piece of work.
The Russians did a lot of work in this area back in the 1950s. If you can read a little Russian, you can always go try their emulator online.