Understanding and repairing the power supply from a 1969 analog computer | Hacker News Reader

Understanding and repairing the power supply from a 1969 analog computer

righto.com

35 pointsrobin_reala12 comments

What's the "Hello, World!" for an analog computer? Can you build it on a breadboard?

Asking while enrolled Electronics 102 at my local community college (diode and transistor circuits, not yet op-amps.)

You can use op-amps to build circuits that add/subtract voltages, scale by a constant, integrate, differentiate. You can combine these to model differential equations. And yes, you can build the equivalent circuits on a breadboard.

Here is a book to learn a little about them: http://www.analogmuseum.org/library/handbook_of_analog_compu...

Yes. Analog op-amp ICs are cheap, fun to play with on a breadboard, and amazingly accurate.

Some op-amp projects: [1] A 741 op-amp in DIP packaging is $0.56 on Digi-Key.

[1] https://bestengineeringprojects.com/operation-amplifier-741-...

For a more modern chip, use TL071/TL081 general-purpose JFET opamp, costs $0.55-$0.61 in DIP.

I actually think that novice hobbyists are better off with the venerable 741 because there is just so much clear and concise documentation on it's use in hobby projects that have accumulated over the years. Once you have a grasp of what the different specifications mean, then it's easy to make the jump to other more modern chips with better performance.

Yes. The 741 data sheet says "The amplifiers offer many features which make their application nearly foolproof: overload protection on the input and output, no latch-up when the common-mode range is exceeded,as well as freedom from oscillations." The newer TL07/TL08 series has 3x the bandwidth (to 3MHz) and can be trimmed to higher precision, but comes with more PC board layout restrictions on the data sheet. For solderless breadboard use, the lower-bandwidth part may be easier to deal with.

(I haven't played with op-amps in years. Back in the 1990s, I tried to build a LIDAR, but I needed more expensive RF-type test gear than I could afford.)

When you can get a 100 MHz opamp for $15 today, 3 MHz is low bandwidth. But I agree, anything faster than TL07/TL08 would be problematic on a breadboard.

On the other hand, a small double-layer circuit board can be as low as $5 nowadays.

"Hello, world" is trivial. But what is the "FizzBuzz" question for an analog computer? Calculate the velocity/acceleration of a failing object under gravity?

Slightly relevant: FizzBuzz might not be so trivial on a FPGA. http://www.righto.com/2018/03/implementing-fizzbuzz-on-fpga....

FPGAs aren't really analog. FizzBuzz is just a counting operation, so the analog equivalent is just a pair of accumulators that discharges to a "Fizz" or "Buzz" led or perhaps a plotter arm if you wanted to print the whole list.

IMHO that would be a blinking LED.

Correct. If he's limited to transistors and basic LRC components, then the typical hello world would be an oscillator into an output. An LED will blink but I think a piezo speaker is funner if you have a turnpot. When you get to opAmps, add a simple microphone (a microphone element can be had for about 5 cents) and feedback to make one of the classic "shushing" devices.

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