# Counting Without Transistors

The Hackaday Prize is all about Building Hope. We want to see hardware creators change the world with microcontrollers and breadboards. That’s a noble goal, but it also doesn’t mean you can’t have fun. That’s exactly what [Yann] is doing with a pile of surplus Soviet components, a bunch of bodge wire, and exactly zero transistors. He’s building a hexadecimal display module using only relays and diodes. It’s absurd, but still very very cool.

The inspiration for this build comes from homebrew computing. With this, there’s a recurring problem of displaying the status of a bus. Sure, a bank of LEDs will work, but then you have to count to F. The better solution to this is a hexadecimal display. The best solution to this problem is using Numitrons — seven segment Nixies, basically — and doing it all with relays and diode steering.

This module accepts four bits as an input and uses a clever arrangement of diodes to turn those four signals into the digits 0-F. Yes, it’s hexadecimal, but that’s just what you do when you’re building your own computer.

Right now, [Yann] has one module on a slim-profile protoboard that should stack easily enough for an 8 or even a 16-bit wide bus. That’s four tubes and hundreds of diodes for the 16-bit version, but the good news is all of these modules are identical, vastly simplifying the construction of the display panel of a homebrew computer.

## 29 thoughts on “Counting Without Transistors”

1. “That’s four tubes and hundreds of diodes for the 16-bit version”
Four tubes : yes
Hundreds of diodes : only 4×59 = 235 (versus 308, without minimization)

1. Sweeney says:

Unless i’ve missed something obvious 235 falls into the category of “hundreds”. What was your point again?

1. it sounded as if Brian insisted on there being a crazy amount of diodes, when in fact there is not so many after all.

2. richfiles says:

When you wire them the way I did, those diodes certainly add up! :P

I built some Diode ROMs to decode single inputs into the correct segments to drive a pair of 14 segment alphanumeric LED displays. It’s for my Kerbal Space Program instrument panel. This is part of my DSKY inspired digital readout block. It’ll tell me things like Altitude, Apoapsis, Periapsis, Inclination, Eccentricity, time to the next “node”, and which node is next (Ap, Pe, SoI, or maneuver node, using the letters A, P, S, or n).

Five of the large diode assemblies will be made, and there is a single small one as well.
https://i.imgur.com/blfdLON.jpg

And here it is working:
https://i.imgur.com/V3Pkbp5.gifv

Honestly, even though it was a lot of work, i got real good at these. I could put one large diode assembly together in a single afternoon, and it puts that reel of over 9000 diodes I got for free to good use as well!

2. frankbuss says:

Numitrons are cool, but for the 16 bit version I would probably use just a microcontroller.

1. Very good, Yann. Most people would have used a Raspberry Pi.

1. Olsen says:

At least it doesn’t need to connect to a remote server to blink an LED!
;-)

2. Olsen : Touché :-P

So my relay-based module “will respect your privacy” !!!

3. “Why …. why would you have to boot a Linux computer just to display digits ?…”

It seems as though that’s the only way most people know how to do electronic design these days…if you can call the results “electronic design”.
“…When the only tool you have is a hammer…”

Again: very good, Yann.

4. jawnhenry : thanks :-)
But it’s only one of many modules ! Wait for the register set, the ALU, the DRAM, the I/O…
(many instances where I’ll need these display modules, by the way !)

5. Dan says:

When the only tool you have in a hammer, it’s often more cost effective to change problems into something that accepts hammering solutions, than to learn a new tool.

6. Markus Stehr says:

“When the only tool you have in a hammer, it’s often more cost effective to change problems into something that accepts hammering solutions, than to learn a new tool.”

That’s very sad, shouldn’t we always strive for the most elegant solution and not simply for the cheapest?

7. Markus Stehr : well it depends…
In my project, I hhad decided on certain crazy rules.
Other projects need “something right now”, others need “cut all the corner until it’s a perfectly smooth circle”…
Here the “elegance” comes from the constraints and the consequences, I had to invent a few tricks.

8. “When the only tool you have in a hammer, it’s often more cost effective to change problems into something that accepts hammering solutions, than to learn a new tool.”

The very best hackers are those who realize new tools are needed, obtain the new tools, and then solve the problem.

“…an engineer learns in order to build.”;
and,
“Well over half of the time you spend working on a project (on the order of 70 percent) is spent thinking, and no tool, no matter how advanced, can think for you…”–Fred Brooks

“We are all born ignorant. To remain stupid requires hard work.”–Benjamin Franklin

3. That’s really cool! Nice project!

1. Thanks !
I hope to inspire others !

4. What’s with this silicon crap on board? Expecting diode tubes there. Perf board? No real project is complete without segmented standoffs screwed to plywood. Rats’ nest rules.
Store bought relays sad. Wind your own. Suppose numi is OK but should have been electromechanical. More windings and more relay clicky goodness. LEDs is just cheating. Grain of wheat bulbs or nothing.
Snicker. Only teasing. Is awesome.

1. What silicon crap ? D9K means Soviet Glorious Germanium Diode (and is historically almost accurate, it’s point-contact, they came before serious, well-chararcterised and cheap silicon diodes appeared in the 60s)
Diode tubes suck unless you want high-speed, HOT switching.
Perf board : For the Protozzzz ;-) I couldn’t find suitable FR2/Bakelite :-( [yet?]
LEDs were not cheating : the “funky proto” uses vintage, 1st generation Soviet LEDs :-P
(and the first LED effects were witnessed in the 30s)
Grain of wheat bulbs : I also have “Glühbirnchen”, look at the video ;-)

” Snicker. Only teasing. Is awesome.” I know :-) But going over all the origins of these parts is part of the fun :-)
Much more fun than FPGA right ? :-)

1. +What silicon crap ? D9K means Soviet Glorious Germanium Diode (and is historically almost accurate, it’s point-contact, they came before serious, well-chararcterised and cheap silicon diodes appeared in the 60s)

Still a semiconductor. Expensive or not has no place there. ????

+Diode tubes suck unless you want high-speed, HOT switching.

Hot would be accurate with that many diode tubes. Tubes suck then they filled with exotic gasses and then suck power until they blow out filament. So they suck and blow. ????

+Perf board : For the Protozzzz ???? I couldn’t find suitable FR2/Bakelite ???? [yet?]

No excuses. Bakelite is still available in sheets and barrier strips.????

That is plain ugly. Boo. No style and no grace. Minus points for linking to it. ????

+LEDs were not cheating : the “funky proto” uses vintage, 1st generation Soviet LEDs ????

(and the first LED effects were witnessed in the 30s)

Seldom used and just showy. Were expensive and if were used to make 7-segment display would’ve been acceptable but noooo someone has to use a numi tube. Nixie wasn’t used so points given. ????

+Grain of wheat bulbs : I also have “Glühbirnchen”, look at the video ????

Well that’s German and definitely mixes tech. malen’kaya lampochka are what is needed. ????

Ya it is fun. More fun than an FPGA? Oh thems fightin’ words round these here parts and this here crowd. Of course your failure to add a LM555 will eventually draw comment regardless of intended era. ????

1. > Still a semiconductor. Expensive or not has no place there.
It has a historical place, for a design that could come from the 50s or 60s :-)

> So they suck and blow.
Thanks for the warming, huh, the warning ;-)

> No excuses. Bakelite is still available in sheets and barrier strips.????
I have some copper-clad bakelite but my swedish sponsor doesn’t handle it. I’ll have to find in China, or find a CNC/mill.

> That is plain ugly. Boo. No style and no grace.

> Seldom used and just showy. Were expensive
That’s why I used them only on a certain “showy” prototype :-)

> Well that’s German and definitely mixes tech.
That’s still historically accurate ;-)

> LM555
not NE555 ? that’s luxury, anyway :-P

cheers, yg

1. + It has a historical place, for a design that could come from the 50s or 60s ????

Mid 60’s and probably have to be working for war department or nice underpaid research think tank operated by glorious Soviet War Department to get ahold of visible light LEDs. Then again transistors would be a lot more available and starting to be cost reasonable/reliable compared to relays by then. ????

> So they suck and blow.

+Thanks for the warming, huh, the warning ????

Very very warming. A mere twenty or so tubes in the family TV were enough to keep a sizable poorly insulated colonial living room warm. That’s dead of winter hovering around freezing temperature outside.
Hundred or so tubes should be perfect for that Siberian winter blizzard.????

> That is plain ugly. Boo. No style and no grace.

Well hoping Dr Cockroach isn’t actually some precocious child who may happen to read this and in which instance should know it’s all in fun. If an adult then not.

Dr Cockroach’s cardboard relay is a pile of garbage. That’s not being fair to garbage. I’ve been yanking stuff from trash and repurposing for years. This is the first time actually nausiated. A six year old should help the Dr make a better design.
There are so many beautiful cardstock models available that he should start there. Like an anime puppy or something.
It made me feel bad and he should feel bad for putting it where someone could see it. ????

> Well that’s German and definitely mixes tech.

+That’s still historically accurate ????

Nuh uh. Not Russian. ????

> LM555

+not NE555 ? that’s luxury, anyway ????

Well it’s the new replacement for NE, SE, SA, and MC1455 so it must be better. Highly engineered to be exactly the same. Not to mention countless hours retooling to spray new ID and changing the label on the die master. Snicker. Having fun.

5. Pete Willard says:

Semantics: I would argue that a Numitron is not a 7 segment “nixie”. It is a 7 segment incandescent display… The NIXIE is the name for true cold cathode “NIX-1” tubes, from the name Numerical Indicator Experiment #1. A TUBE based display does not imply it’s automatically a NIXIE, just like Vacuum Fluorescent displays are not NIXIE tubes.

1. mjrippe says:

+1

Even the generic “nixies” made by others than Burroughs/Haydu use neon gas.

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