On Tue, Jul 23, 2024 at 2:20 PM Rick Bensene via cctalk < cctalk@classiccmp.org> wrote:
> Dwight wrote: > > > As a kid, I used a handful of radioshack relays to make a sequenced > electrical lock. One had to > > enter four each four bit numbers to turn on the lock. Any wrong number > and you had to start over. I > think that was first the first time I did a > logical design. You'd set the 4 toggle switches for the > next number in > sequence and then enter it. > > Not a computer but then, I was just a kid. > > Like minds, I guess. > > I did the same kind of thing when I was a kid, too. Except, we were > pretty poor, and couldn't afford Radio Shack relays. I had to make my own, > out of 1/4" plywood scraps for the base, tin snipped from coffee can lids, > nails for pivot points, wire-wound nails for electromagnets, and tacks for > contacts. I made both usual relays was well as relays with two coils, one > to set the relay and another to "unset" it (latching). The wiring was all > telephone wire, from a 50-pair cable that my Dad found somewhere and gave > to me. My sequential combination lock was for a "burglar alarm" I made > for my bedroom door. I made my own keyboards using similar materials, but > mine were decimal, encoded with diodes that a neighbor who was into > electronics gave to me. The combination was four digits that had to be > entered in the correct order on the keyboard outside my door. I also had a > keyboard next to my bed that allowed me to override the alarm if someone > knocked to come in, as well as to reset the password at any time. The > password was stored by sixteen of those set/reset latching relays. The > four digit password had to be entered entirely, then an "ENTER" key > pressed, and if there was an error anywhere in the password, as soon as > ENTER was pressed, the alarm would go off, which was a ringer salvaged from > a telephone that someone gave me. The only way to shut off the alarm was > to enter the correct code. If someone opened the bedroom door when the > alarm was set (by entering the code) the bell would start ringing. The > transformer from my train set powered the thing. It worked reliably, but > my Mom grew tired of it quickly. Not easy to enter the code with a > basket-load of clothes in her arms. I learned a lot from making that > thing. The hardest part was making the sequencer that would step as each > digit was entered, then compared the entered digit against the > corresponding digit of the stored code. That took quite a few relays. I > got quite good at making the relays so that they were reliable and > consistent in their behavior. It was a total rats nest of wiring on a > piece of larger plywood that leaned up against a wall in my room. > > A few years later, I built a four-bit binary adder using a bit-serial ALU > and sequencer made with old telephone relays. > > The two numbers to be added were entered using a keyboard I made from a > salvaged touch tone telephone keyboard. Then, an ADD (#) button was > pressed, and the sequencer (which was made with a motor that turned a drum > with contacts made from sheet metal screws) would step through selecting > each group of two bits, adding them, saving the carry, and then moving onto > the next two bits. The result was displayed on five #47 lamps. It was > not particularly fast; the fastest I could make it go would give a result > in about 1/2 second. Trying to run it any faster resulted in errors, > probably due to issues with the design rather than the relays themselves. > The thing covered a tabletop, again wired together with telephone wire. I > tired of it pretty quickly because it just added numbers. I had visions of > somehow making a memory out of relays and making some kind of programming > method, again probably using a drum with contacts that would close when a > screw was screwed into the drum, such that it could run short programs, but > I didn't have the space to build out the rest of it, so, I eventually took > it apart so I could have my table back. > This is a very cool story, Rick. > What I'd give to be able to have all that free time during the summer when > school was out. Virtually no real responsibilities (mow the yard, keep my > room "clean", do dishes) - just limitless time to dream up projects to > build with limited resources. I had no training in logic design, I just > kind of figured it out as I went along. > Those truly were the days. Sellam
