An intersting use for phone relays [telecom]

The museum in my city used to have a mechanical "Tic Tac Toe" (Noughts and Crosses) machine that you could play and it was made mostly of old SxS relays and linefinders etc. (I only found out what they actually were years later when I was introduced to Step exchanges).

This was back in the 1970's and it didn't take long to work out how to defeat the hardwired logic and win every game, but it was a pretty effective "kid magnet" and was very popular for the junior tech-heads.

I don't know if it still exists, but it would be an exhibit in its own right now on the old technology used let alone the pioneering use as an entertainment device!

This is a bit more complicated than the science fair project I did about 50 years ago.... My project was a 32 bit, two input binary adder. I was working in a hardware store at the time and my boss had a friend in the pinball machine business who donated all the relays.

A neat feature was when you added 0001 to FFFF you could hear the carry (it was a ripple carry circuit) for a couple of seconds, then watch the transformer smoke a bit. Pretty cool for its day.

BTW, I got an honorable mention at the science fair (maybe because of the smoke...)

ET

***** Moderator's Note *****

Please tell us why a carry overloaded the transformer.

Bill Horne Moderator

It was a bit too much?

(So sorry.)

Frank

A tourist-attraction food court and fish market on Cannery Row in Monterey CA used to have (maybe still does) a live chicken in a glass-front enclosure who played Tic Tac Toe against all comers.

You put in four quarters; punched a button for your first move; a light lit up on a corresponding square on the back of the enclosure; the chicken made its move by pecking a square on the same board, and instantly swiveled around to get a grain of corn that dropped into a cup on the side wall; and so on.

The chicken beat me fair and square -- and a loudspeaker blared out "Chicken wins!" for the entertainment of all the bystanders.

(You know, I just now realized, very possibly the both had some logic-driven electronics that activated a small buzzer or infrared light source in the appropriate square to communicate to the chicken where it should peck each time. If so, this clearly continues to be a telecom- (or tell-a-chicken)-related topic . . . )

It was indeed, we often used them at "open houses" to show off what technology could do, just like your telephone system. Those date back even before tranasistors.

I guess no one remembers when there we "All-Relay" central offices. Not practical in large offices, but for a CDO is a small place they were very effective and took up little space.

Wes Leatherock snipped-for-privacy@yahoo.com snipped-for-privacy@aol.com

A 32 bit adder has a total of 95 relays. Setting up all ones in one input and then a single, least significant one in the other causes all the relays associated with the first input and all the carry relays to pull in, a totatl of 63 relay coils. This is an extreme case (all ones in both inputs is worse as it causes all the relays to operate, which also smoked the transformer, but it didn't make such a pleasing noise...). In short, the transformer was under rated. I should add that the equipment I designed for the old Bell System had power supplies with better ratings....

ET

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Because the transformer was undersized, of course.

More seriously, because all the 'carry' operations, caused all the relays to fire.

It's a reasonable guess the pinball-machine salvage was in large part 'latching' relays, which (like CMOS) draw power only when changing state. A 'carry' across all the bits meant that all the output relays, as well as those driving the 'carry' lines, changed state,

Actually there were no latching relays used, just a transformer that was more than a "wee bit" too small....

ET

PS - the real work was changing the contacts on the relays to provide the required logic. I still have some of the left over parts....

When I was a kid, the Boston Museum of Science had such a thing, and it had a complete logic diagram of the thing with neon bulbs that came on to show the system state and how it changed as you made each move. Which of course made it easier to learn how to defeat it.

It has since been taken down, which is a tragedy since it's really one of the best introductions to electronic logic I have ever seen.

--scott

I found an old switchboard* and used a lab dc power supply to run it. If I had too many cord circuits in use at once the power-supply fuse blew, and the lab tech got tired of replacing them. But it was certainly enough power to light the lamps and provide talk current. (I didn't have an ac power supply, so ringing was done by hand cranking and that was stiff--heavy cranking produced merely a light tinkle on the phone.)

Regarding the logic of calculators, IBM has posted the specs for its

603 electronic calculator (punched card machine) of the 1940s along with other information on it, as part of its Centennial:

IBM 603 overall: (note sublinks)

603 tube specs: 603 manual: *The switchboard was a Kellogg and provided intercom service only. It had no trunk circuits so I could not connect it to my house line. It was also in poor condition. After gathering dust for years I gave it away.

Along these lines, the Bell System Technical Journal had a 1950 article discussing relay memory requirements for telephone exchanges. Relays could have two stable states. Rather technical in terms of math.