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 voltage 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. Hi 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 terms. 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 ). 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. Dwight