4 bit - 4 stage Binary Adder / Subtracter  using Yaxley type switches - 1963 project

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

These were the days long before integrated circuits became widely available and within financial reach of the casual 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 15 / 40 pence each in 2006.

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

Although incandescent 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 of the ac phase.
This also gives the advantage of not having to worry about the wiring polarity of the LED's when wiring the circuit.

If using a dc output supply, then correct polarity of the LED's must be observed when wiring each in the circuit.  

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Schematic

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