Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Constructing an 8-bit relay computer from scratch

relaycomputer.co.uk

Post reply on HN
Print view View original

21–30 of 39 posts

Re: Constructing an 8-bit relay computer from scratch

#21

Post by labawi »

OnACoffeeBreak wrote: post #8
amelius wrote: post #3

Can anyone explain why the contact DC voltage rating of relays is often much lower (5x is no exception) than the AC rating?

As the other poster pointed out arcing is one component. Another is that DC voltage equivalent of an AC voltage is the RMS value of the AC signal. So, V_AC_RMS = V_peak / sqrt(2).

AC specifications are usually in RMS equivalent voltage so 1A 10V AC is same power as 1A 10V DC. This makes the peak difference larger, not smaller.

AC is easier to extinguish (0A current 100 times / s), and I believe the reversible direction makes for better electroplating characteristics.

Re: Constructing an 8-bit relay computer from scratch

#22

Post by userbinator »

The architecture looks vaguely similar to a Motorola 68HC12, down to the big-endian encoding. Quite ambitious considering that it has more registers than a 6502.

Note that while most people here seem to associate relays with large clicking things, there are reed relays which are much smaller and faster, and also practically silent:

https://en.wikipedia.org/wiki/Reed_relay

...and people have built computers using them:

http://www.xpl0.org/rr6/

Re: Constructing an 8-bit relay computer from scratch

#23

Post by whatatita »

bloak wrote: post #6
superzamp wrote: post #2

Clicked for the sound, was not disappointed.

Yes. Also the blinkenlights are very satisfactory. And very nice casing. What is the clock speed at the end of the demo? It sounds like about 8 Hz.

He mentions in an earlier video that the fastest speed the closk can run at is 32Hz.

Re: Constructing an 8-bit relay computer from scratch

#24

Post by segfaultbuserr »

alufers wrote: post #4
amelius wrote: post #3

Can anyone explain why the contact DC voltage rating of relays is often much lower (5x is no exception) than the AC rating?

I think it is due to arcing. With AC an arc will extinguish itself itself when the voltage goes through 0, but for DC no such thing occurs and an long arc can damage the relay contacts.

Also, an interesting oddity about relays and switches: many have a minimum current rating because some arcing is actually required, it burns off the oxidation layers on their contacts. This is called "wet switching", if you use a wet-switching relay to toggle a control voltage with negligible current flowing on the line, you can drive the relay to death prematurely due to oxidation. The solution is to use a control current instead of a control voltage, but it has higher power consumption (on the bright side, better noise immunity). There are also specialized "dry-switching" relays to solve this problem, usually for test and measurements applications (but using them to switch live circuits causes the opposite problem - arcing will damage them).

Re: Constructing an 8-bit relay computer from scratch

#25

Post by bittercynic »

Very impressive!

At the last Vintage Computer Fest West before covid I saw this on display [1] and was completely taken with the clicky sound and blinkenlights. It does use semiconductors for the memory and IO.

I built one last March and April, and found it to be surprisingly enjoyable and relaxing. Highly recommended for those who love clicking and blinking things.

[1] http://relaysbc.sourceforge.net/

Re: Constructing an 8-bit relay computer from scratch

#26

Post by kpgraham »

In my senior year of high school (1968-69) Mike Sivy (Yes that Michael Sivy) and I tried to build some components of a digital computer out of military surplus relays. We took the bus and the subway down to Canal Street in NYC and bought a box of large 24 volt relays. We designed a counter and we were able to get some parts working. It took 5 relays for each part, which Sivy was able to drop down to 4 by using a diode. I always thought that the diode was cheating and by using it we lost the purity of the concept, but we had a limited number of relays and we wanted to count to 8. One of our problems was hysteresis and at various times the whole thing would start sparking and chattering like crazy. I remember trying to explain what we did to parents that wandered into the physics lab in the school's open house. They were more impressed with the giant "jabob's ladder" we built that eventually set the lab's window moulding on fire.

Re: Constructing an 8-bit relay computer from scratch

#29

Post by sitkack »

Robotbeat wrote: post #19
dvh wrote: post #9

Could this kind of computer work at 450°C?

Yes, you could. But there are also specialized electronics that work at 450C (or even 500C). NASA Glenn Research Center has developed them. Transistors and such using Silicon Carbide (instead of regular silicon). A simple computer could as easily be made with such transistors and passive elements. It’d be much faster and lighter than a relay computer. The issue with all such computers is developing significant storag…

Ozark Integrated Circuits got a contract from NASA to develop a high temperature RISC-V chip.

> Ozark IC will create the first 500-degree Celsius RISC-V multi-chip system in a package as a way to illustrate the techniques, design procedures and the multi-chip package with high-temperature components that go into creating a high-temperature electronic system.

press release https://talkbusiness.net/2020/05/nasa-to-give-750000-to-ozar...

Their banner says, "We Design for Venus" https://archive.is/w0lZV/image

https://www.ozarkic.com/

Re: Constructing an 8-bit relay computer from scratch

#30

Post by opwieurposiu »

frabert wrote: post #14
imglorp wrote: post #13

Earlier quoted context omitted.

That's a great question if you're asking about using it on Venus. Copper melts at 1084 C, so you're good there for springs, conductors and contacts. You'd need insulation for wires and circuit boards: something like fiberglass weave would be good up to 537C. No solder, wire wrap, steel posts. Resistors and capacitors for RC circuits should be similar, carbon is good and capacitors are insulator/conductor layers. I su…

> Copper melts at 1084 C, so you're good there for springs Would you really be able to make a spring out of copper? It is my understanding that copper work hardens very quickly, which is a big no-no if you're making a spring, I guess

For springs you have to use Beryllium copper

https://en.wikipedia.org/wiki/Beryllium_copper

Post reply on HN