Relay computers - OR functionality

From: Dwight K. Elvey <>
Date: Mon Sep 27 16:47:27 2004

>From: "Dwight K. Elvey" <>
>>From: "Steve Thatcher" <>
>>you create your OR functionality with diodes - use two diodes (or as many
>inputs as you need) such as the 1N4001 for your inputs. Tie the cathodes
>together and attach that to the relay coil. Apply "logic high" (whatever
>your relays operate at) to either (or any) diode anode and the relay will turn
>on. The relay can be the next stage and does not have to be there to implement
>the OR.
>>best regards, Steve Thatcher
> You don't need the steering diodes if the lines that provide the
>terms don't cross talk to other coils. This is pure relay logic
>and works with AC relays as well as DC. The diodes are only
>needed when you share complex terms that use the same stack of
>contact terms but would otherwise cross talk. The diodes allow
>one to optimize the number of contacts used by sharing common
> Each relay contact can be used as a term in an equation. Normally
>open contact can provide inverting function and normally closed
>contact can provide isolation buffering ( needed for AC but can
>be optimized with diodes in DC ).

 Should have said normally closed provide inverting and
normally open provide buffering.

> Designing with relays takes a slightly different mindset than
>with normal logic, like TTL. You have to think in terms of
>inverters and transmission gates. There are no NAND or NOR
>gates. The function of NAND and NOR is constructed by sharing
>the contacts of several relays and then using that shared
>stack to control the output ( that may be another coil of
>a relay ).
> Stacking contacts can provide AND like function and paralleling
>contacts can provide OR like function. Choice of normally
>open contacts provides OR and AND with inverted inputs,
>the Boolean equivalent of NAND and NOR.
> This takes a little more thinking of design because with double
>throw relays, one has to think of the source as providing the
>inverting and non-inverting signals. The contacts only provide
>OR and AND, depending on how they are arranged.
>>Question: Wouldn't it be easier to implement an OR gate with no relays at
>>all (just two wires joining together)? Or would you need to use the relays
>>to keep the output voltage/amperage regulated?
Received on Mon Sep 27 2004 - 16:47:27 BST

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