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A sick trick for the multiplies

A project log for SPDT16: 16-bits arithmetic unit with relays

Let's imagine I could get about 200 SPDT relays. Of course I would know what to do with them :-D But will 200 be enough ?

Yann Guidon / YGDES 05/01/2016 at 09:100 Comments

The algorithm for multiplication is pretty easy. If the multiplicand bit is set, add the multiplier to the shift register.

The initial idea was to use a MUX2 to select between the last result (shifted register) or the new result (oh, wait..... nevermind)

But that's typically an electronics-minded design.

Moving backwards, I realise that the multiplier is just a set of manual switches. They are either tied to +Vcc or left open.

Wait.

What if the +Vcc was left open too ? That would add nothing. Which is the desired behaviour for the multiplication by 0. Bingo !

So now, I saved a row of quite a lot of relays, just by routing the multiplicand bit to the +Vcc of the multiplier's rotary hex switches...

(schematics left as an exercise to the reader, or be patient, I must buy groceries...)

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