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So, you want a simple digital logic function in a synthesizer. Maybe it's an AND gate, or a couple of XORs, maybe as much as a shift register. How will you build it?
Today it often makes sense to just throw in a microcontroller chip. They're cheap and versatile. The same microcontroller can be programmed to serve many different purposes, so you can keep just a few types of them in stock, buy them in huge quantities, and that keeps costs down. If you need more speed, then it may make sense to use FPGAs (field-programmable gate arrays), but very few synthesizer circuits really need that much speed.
Twenty or thirty years ago, before microcontrollers were cheap, the usual way of doing a small amount of digital logic was to throw in a couple of MSI (medium-scale integration) logic chips, such as the 7400 or 74LS00 series based on bipolar transistors or the 4000 series based on CMOS. These were small logic building blocks, typically a few gates on each 14-pin or 16-pin DIP chip. There were dozens of popular chips in these series and a few hundred less-common ones. They first existed in the late 1960s but weren't cost-effective and readily available to hobbyists until the mid-1970s. Such chips still exist and you still see a lot of them in DIY designs, but they're gradually falling out of production as cheaper microcontrollers become more appealing to the large commercial interests that are most of the market.
Even further into the past, integrated circuits of any kind were too expensive to be the first choice for hobbyists, and we had to build things out of one active device (transistor or even tube) at a time. I used this kind of logic in my MSK 012 Transistor ADSR. Logic gates built with the minimum number of transistors are barely digital at all: they may be better understood as analog amplifier circuits that happen to be amplifying digital signals. The chips we usually use today, and the gates inside them, have become more complicated and involve more transistors as transistors have become cheaper, but they can be understood as just evolutionary developments from the simplest possible gates.
(Score: 2) by Immerman on Monday June 22 2020, @03:05PM (5 children)
Relays are (and were) rarely used for computational purposes since they are extremely slow and power-hungry. And loud. Once vacuum tubes were invented they were superior in almost every way. And of course transistors were another big leap forward beyond those.
(Score: 4, Interesting) by DannyB on Monday June 22 2020, @05:48PM (4 children)
As a teen, I remember building a "combination lock" out of relay logic. Ten key "pad" -- really ten momentary normally open contact round push buttons, mounted in heavy cardboard box. Six relays. Five of them were wired so that pressing the first digit of the combination energized 1st relay, whose closure provided positive voltage to it's own coil (for when you released the push button), and provided positive voltage to the next button in sequence, so that pressing it, could energize the 2nd relay. The 2nd relay similarly also energized its own coil, and provided positive voltage for 3rd button, etc. Finally energizing the 5th relay completed the combination. The sixth relay was energized by the five digit buttons which were not part of the combination. Pressing any of those five unused digits energized the sixth relay whose normally-closed contacts provided power to the sequence of the first five relays. Thus pressing any wrong digits, reset the partial sequence of energized relays.
Problems:
Suppose the combination were: 1 2 3 4 5
Once you pressed 1, as long as you only continued to try 2, 3, 4 and 5, nothing would de-energize the first relay. So by trying long enough without pressing 6, 7, 8, 9 or 0, you could eventually energize the fifth relay thus completing the combination.
Hey, I was a dumb kid. Before I could get my hands on a few bits of TTL. Before I got my hands on a programmable calculator, at which point, I never again picked up a soldering iron. Now I don't even remember which end of a soldering iron to pick up.
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(Score: 1, Funny) by Anonymous Coward on Monday June 22 2020, @08:16PM
Don't worry there. If the iron is on, you will only mistake the ends once, then you'll remember which end is which again for a very long time.
(Score: 2) by Immerman on Tuesday June 23 2020, @01:44PM (2 children)
I suppose what you'd want is to de-energize 1 if any button *other than* 2 is pushed... Hmm... I want to say adding a pull-down resistor between the coil sink and ground, with the sink also wired directly to every button except its own button and the next. Push any other button and the low side of the coil will be pulled high, de-energizing the relay. That's a lot of wires though, and you'd also need to do something to isolate buttons from each other... a diode between each button and the coil sink would do the job. That's 8 diodes for each relay though, and incorporating additional logic on the ground side of the circuit is probably a bit over the top for a kid just teaching himself how to play with relays.
(Score: 2) by DannyB on Tuesday June 23 2020, @02:12PM (1 child)
I would not have thought of that in 1975. At the point I built this relay thingy I was already thinking about TTL and pure digital logic. TTL was useful to think of pure boolean logic without having to give much thought to electrical characteristics -- mostly.
Before I had tried out an adult friend's programmable calculator (an HP somethingorother about $400), I was drawing logic diagrams for digital clocks, and for calculators that did addition only. The combination lock had been a first, but earlier step. The calculators logic complexity was what gave me an appreciation for microprocessors -- which were conceptually simpler. At least each major functional block was understandable on its own, and you put them all together. I remember a 4 big tutorial processor in Popular Electronics, I think called PIP. It wasn't intended to be useful, but was my first "Ah Ha!" experience understanding a microprocessor that used a simplistic microcode.
I still have a few hand written yellow tablets of these things from about age 14 on to late high school. Over the years I've gotten rid of a lot of things, but selectively keep a few things that remind me those days were real.
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(Score: 2) by Immerman on Tuesday June 23 2020, @03:14PM
Yeah, boolean logic does simplify most things considerably, enough so that the loss of clever leveraging of the underlying electronics is very rarely an issue. I still remember designing and building a simple calculator as part of an engineering class - I forget if it was one or two digit, but it supported subtraction as well via twos-complement addition. What I remember most was that it was enough work to convince me to stick to software.