I am going to do a completely silly project and build some logic gates using some 5 volt relays. The data sheet says the coil resistance is 130 ohms and 192 mW power. I think this means that roughly 38 mA of current will trigger the coil, which is pretty small.

These relays already have a fly back diode built into their coil, so no need there. But I want to use two diodes as inputs to create an OR gate, and use that to a relay inverter to create a NOR gate. Now if these were transistors I would use switching diodes for this purpose, but relays aren't transistors. However, 38 mA seems small enough that switching diodes would work here too.

Does my reasoning seem sound?

If anyone is curious, I want to build something like a relay counter and make a lot of noise while using the logic outputs to turn on some blinkenlights. Basically a really slow and noisy output device with a 50s retro-future vibe.

What a delightfully silly project! And yes, switching diodes should be fine, as they're generally rated for more current than that.

I like the counter idea. However, it might take some monkeying to make it work. To form each flip-flop, I'm imagining you'll have two relays cross-coupled to form a multivibrator, is that right? And there'll be some capacitors whose values need to be experimented with...

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Thanks. Yes, some relay flip flops will form the basis for the counter. You're correct that some capacitors might be needed, but the whole thing is going to take some trial and error as relay logic isn't something I have done much of.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

@BDD, thanks for the schematic and the data sheets.

I contemplated going with some 24 volt relays in a clear housing, which would both make louder switching sounds and be more visible while doing it. But I got a really good deal on some Meder 5VDC DPDT relays. Basically $1 each from Electronics Goldmine which occasionally has some screaming deals. I got some nice gear motors from a sale a while back.

So I bought 30, which should be enough to build various logic gates and then Voltron them together into counters or maybe an adder.

I resisted the temptation to buy the two hundred it would take to build a relay computer. That would be a 1 bit wide serial ALU machine using serial flash and ram. Most of the relay machines online use semiconductor memories as building RAM and addressing decoders using relays is not for the faint of heart.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Nothing like a little space heating while doing computing work

Neil

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

The first relay computer I saw online was Harry Porter's https://web.cecs.pdx.edu/~harry/Relay/, and he used semiconductor RAM to avoid that explosive parts count. Even with that compromise it is a beast.

The Mercia relay computer https://www.relaiscomputer.nl/index.php uses over 2000 relays and has just 512 bytes of RAM. He also used diode ROMs with in relay decoders for the microcode and ROM. Besides the expense, where do you keep such a beast?

Fortunately, I have two rarely used bedrooms and respectable cellar space. Unfortunately, I have been forbidden from putting 'your bloody toys' in them

(Also I have to pay the power bill! Though I suspect they might be lower than Usagi Electric's valve systems.)

Neil

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Ah, but the opportunity to make a solar powered relay computer, even if it could only run when the sun shines! At least you could go straight from the 28v or so the panels provide without having to bother with all that mains interfacing stuff

My office/workshop lives in the attic at the top of the house, with a small mechanical workshop in the cellar. It works pretty well, apart from the occasional Murphy's law of requiring a tool from one while working in the other...

Neil

Relays seem to have more varieties than transistors. They differ in voltages, number of contacts, AC versus DC, and now they even have different switching speeds!?

What I want are decorative relays with clear cases that make noise as they switch! Plus some blinkenlights.

At the suggestion of Dr. Matt Regan I took a look at Dieter Mueller's relay ALU which is here: http://www.6502.org/users/dieter/a3/a3_4.htm
It is a marvel of economical design.