atomic_fungus (atomic_fungus) wrote,
atomic_fungus
atomic_fungus

#7685: If I knew then what I know now...

There are so many things that I thought were more complicated than they actually are.

My favorite example is digital logic. When I was a teenager, looking through the Radio Shack catalog, I always would look at the digital logic chips and wonder what kind of electronics wizard would know what to do with them.

...a few years later, in school, I rapidly learned that digital logic is dead simple.

The simplest gate is a NAND (not and) gate. It has two inputs and one output. The table showing the gate's output, given the possible inputs, is called a "truth table" and the one for a NAND gate is as follows:

A B C
0 0 1
0 1 0
1 0 0
1 1 0

A and B are inputs, C is output. You can build an entire computer using nothing but NAND gates, if you know what you're doing. It will be a lot more involved than a computer built using other gates as needed, but you can do it. The benefit of the NAND gate is that it is the easiest logic gate to fabricate, requiring the fewest transistors; only the inverter ("NOT") requires less.

NAND is basically an AND gate with an inverted output. AND's truth table:

A B C
0 0 0
0 1 0
1 0 0
1 1 1

Then we have a few others which are useful. I'm going to show the OR gate; NOR is just the same with the outputs inverted.

A B C
0 0 0
0 1 1
1 0 1
1 1 1

And then there's XOR, exclusive OR:

A B C
0 0 0
0 1 1
1 0 1
1 1 0

So we have NOT, NAND, AND, NOR, OR, and XOR. With those six gates you can build anything.

...as long as you don't need an analog output, that is. Digital logic expects two voltages, either high (1) or low (0). Anything else and you have a problem.

* * *

See what I wrote up there? That is all the theory you need to start building digital circuits. Oh, you'll want a few practical points, such as the fact that a TTL output can run up to 10 inputs. You'll also need to understand, in some cases, the functions of pull-up and pull-down resistors. For more complicated circuits, you're going to want to learn how to simplify truth tables so that you don't spend a lot of gates implementing redundant functions. Some of the things you want to do are so common that they make chips to implement those functions: latches, decoders, counters, comparators, flip-flops, and so on. For the most part, pin 1 on the IC is +5V, and the last pin is ground.

Basically, digital logic is like LEGO or TinkerToys: you have a bunch of blocks you can stick together to make what you want. It's a hell of a lot less complicated than it looks from the outside.

Though, if I had known all that in 1982, I could not have afforded to buy the stuff to build my own circuits anyway.

* * *

When I was in my early teens, welding seemed like an arcane art. Fantastically expensive equipment and advanced training were needed to do the simplest tasks. Having something welded was expensive and the shops charged you $15 just to light the torch, before doing any actual work.

*sigh*

Of course, you can weld with coat hangar wire and a car battery. If all you want to do is to fix a minor crack in a bike frame or something, you could probably do worse. You need to know what you're doing but you can do it in an emergency.

Even at the time you could get a low-duty-cycle buzz box for about $100. To a 13-year-old in 1981, though, $100 was a lot of money--not the least because $100 was worth considerably more then than it is now. When I wanted to get a VIC-20 they were priced at something like $500. In 2020 dollars, that's $1,200. The $100 buzz box costs nearly $300 in 2021 dollars. (My Harbor Freight flux-core welder cost what, $100? In 2005?)

Welding dovetails with auto repair.

1983, my dad parked the Blue Bomb and did nothing with it. The engine had thrown a fuel pump and the crankcase filled with gasoline. After that was fixed it wouldn't stay running; when you could keep it going, it would run on seven (or six) cylinders.

I didn't know dick about cars. I could rebuild a small engine with my eyes closed but when I looked under the Bomb's hood, it seemed impossibly complex. The culprit, I was told, was the camshaft; replace that and the engine would run fine.

...much later I was told that cars of that vintage had a problem with their smog pumps failing, which would cause a miss exactly like it had. Remove the smog pump, put pipe plugs in the manifold, and turn the idle down a bit--probably an hour's work and $5 worth of parts, and it would have been usable.

If I knew then what I knew now, I could have fixed every single problem that car had, including the rust. Given, oh, the tools, and the parts, of course.

* * *

Don't even get me started on women.

* * *

These days, I tend to do the opposite: thinking that things are easier than they look. I'm not sure when the switch happened, but I went from "Oh crap that's too complicated" to "I can do this!" It was about the time that I started going to school, so maybe it was the revelation that electronics were not a black art but mere engineering that did it.

Also, being an adult, with adult resources, helps. If I need a tool to do a job correctly, and it's not egregiously expensive, I buy it.

* * *

There's no real payoff for all this. Just random musing.
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