Simple Analog Computer (Electronic Slide Rule)

Description

This is my version of an electronic slide rule, which was often called a simple analog computer in the 50s and 60s. I also want to make a hub for information about these because it's really spread out. They make a nice introduction to the point of analog computation, but don't seem to have been made since the 1960s. I tried to give mine a 70s computer vibe.

Goals:
- To recreate a simple computer as a learning tool
- To raise awareness/educate others to its history
- To get a better understanding of the history of the circuit used
- To share designs with others.
- At some point I'd like to make one with high-precision pots

Details

BACKGROUND

The simple analog computer is essentially a comparator circuit where balancing the circuit gives you an approximate answer to several mathematical functions. It functions similar to a slide rule. I don't know what the earliest version of this is, but they were common in the late 50s and early 60s as kits.

The ones I am aware of:

1958 - Mr. Math in June issue of Radio Electronics (https://worldradiohistory.com/Archive-Radio-Electronics/50s/1958/Radio-Electronics-1958-06.pdf)
1959 - Calculo Analog Computer Kit (http://www.ccapitalia.net/descarga/docs/1959-calculo-analog-computer.pdf)
1960 - Edmund Analog Computer (https://computarium.lcd.lu/photos/albums/EDMUND_ANALOG_COMPUTER/album/index.html)
1961 - General Electric Project 4 Computer (EF-140) (http://www.ccapitalia.net/descarga/docs/1961-general-electric-EF-140.pdf)
1962 - American Basic Science Club Analog Computer (https://t-lcarchive.org/american-basic-science-club-analog-computer/)
196? - Mac-1 Mini Analog Computer (http://www.vintage-icl-computers.com/icl48d)
1966 - Pot Computer in January issue of Electronics Illustrated (https://worldradiohistory.com/Archive-Electronics-Illustrated/Electronics-Illustrated-1966-01.pdf)
1969 - Science Fair Electronic Computer Kit (https://www.computerhistory.org/collections/catalog/X744.86A)
2008 - Calculatoria (http://www.nicolamarras.it/calcolatoria/calcolatrice_analogica_en.html)

In December of 1961, the Edmund Analog Computer and G.E. EF-140 were described in an overview of this type of circuit in an article in Popular Electronics (https://worldradiohistory.com/Archive-Poptronics/60s/61/Pop-1961-12.pdf).

More recently, similar instructions were given to explore this circuit as a school activity in https://schoolbag.info/science/laboratory/8.html. The circuit was also implemented with high-precision potentiometers in 2008 as listed above.

I would be very interested in any other versions of this or more information about these. Specifically, more information about the Mac-1 and copies of the manual for the Edmund Analog Computer and the Science Fair one. Here's a summarized version of the Edmund manual in Czech (I think): http://dexovo.cz/analogove-vypocetnictvi-edmund-cast-i.php.

Files

diydials.png

Blank dial areas for custom gauge values/spacing which may be different depending on the potentiometers chosen.

Portable Network Graphics (PNG) - 912.80 kB - 02/07/2021 at 08:29

Preview

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AnalogC.png

The graphics for the Analog Computer with some 70s design flair.

Portable Network Graphics (PNG) - 814.94 kB - 02/07/2021 at 08:27

Preview

Download

Components

2 × 50 Ohm potentiometers

1 × 1K Ohm potentiometer

1 × SPDT Switch

1 × 2 1/8" headphone jacks

3 × Knobs

Project Logs

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Construction
deftcoyote • 02/07/2021 at 20:24 • 0 comments
The pieces used to build the analog computer.
- 3 knobs that are 3d printed (https://www.thingiverse.com/thing:3460654)
- 3 potentiometers (Two 50 Ohm, One 1K Ohm)
- 2 springs
- 2 headphone jacks
- 1 SPDT switch
- 3 pringles lids or circles cut from clear plastic
- battery holder that is 3d printed (https://www.thingiverse.com/thing:3115171)
- a pencilbox :)
For space, I overlapped the 3 potentiometer gauges. Rather than 3d print needles, which might hit each other, I glued the plastic circles to the knobs and drew a line on it for the needle.
The face of the computer with the gauges was laminated and glued to wood. I thin added side walls to mount in the pencilbox. I also 3d printed a battery holder for AA batteries. Again this is wired for either the voltage or the audio input. The finished bottom looks like this.
And that's it! There's a lot to be said about the actual potentiometers used. The tolerance should be less than 5% in order to get fairly accurate results. Using 20% tolerance means that between the 3 pots, your error could be too large to be useful.
I included in the files the gauge section without any numbers as well. This allows you to mark the gauges specific to your pots so that they're more accurate.
Headphones or meter?
deftcoyote • 02/07/2021 at 08:25 • 0 comments

The article in Popular Electronics discusses how there are two ways to make this circuit. You can test whether the comparator is zero by using a galvanometer (or potentiometer) if you give the circuit a voltage. However, if you feed it an audio signal, you can use headphones to hear when the sound is silent. Most of them used the meter, but some like the G.E. kit used headphones.
I am going to use both. I want it to be relatively cheap overall, so I don't want to embed a meter into the computer. I'm going to have two posts in order to attach a potentiometer, but I'll also have audio input/output jacks. A simple switch will select which to use- so the audio option is essentially off.
Here's the version with the meter.
Here's the version with headphones.
You can see that they're essentially the same circuit, so both can be wired with a single switch. These images come from the Popular Electronics article.