4 bit - 4 stage Binary Adder / Subtractor  using Yaxley type - 2 way - 6 pole switches - 1963 project

This is a scan of the original "Simple Binary Adder / Subtractor"   which I built when my age was 12 years (1963).

These were the days long before integrated circuits became generally available and within sensible financial reach of the casual electronic hobbyist.
Even the ubiquitous SN7400 quad NAND gate and SN7483 (4 bit full adder) TTL chip's cost over 1 each in 1971, current cost approx 25 - 40 pence each in 2010.

The schematic circuit uses 9 x hard wired 2 way 6 pole switches and torch bulbs.

Although incandescent torch lamps would give a more primitive (1960's) look and feel to a project of this kind,
today it would be simpler (and cheaper) to use LED's with a series current limiting resistor of 220 ohms using a 6Volt ac supply. 

A suitable power source would be a standard transformer block providing 6V ac output at 300mA would suffice for an all LED version.

No need to rectify the ac output. The LED's will conduct on the forward biasing phase of the ac supply.
This also gives the advantage of not having to worry about the wiring polarity of the LED's when wiring the circuit
Should you use a dc output PSU, then all LEDs will need to be wired for correct polarity.

 

PDF (sorry for poor quality of text)

Scanned text as jpg images.  

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Schematic

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