how best to use momentery switches to control relays?

[PRR]

Wait, I missed this.....

> 1 contact NC, 1 NO

Then it *seems* you knew what to do from the first. I *think* the 2-contact NC NO plus a relay makes a clocked flipflop. It's been a while since I debugged relay ladders.

Global OFF is of course just breaking the relay power.

 

[sahib]

48 relay outputs and 48 switch inputs is a minimum 96-pin chip.

Since no stock controller has 96 I/O pins, you mux to a whole lot of 16-24 pin chips. You are just adding wires.

If you put a few more contacts on each relay, you should be able to do it all without any Silicon. Pre-1980 elevators did an amazing amount of logic with just clever relay-rigs.

No. We are using two chips.

On Tx there is one with 48 inputs and serial output with two pins. Same on Rx in reverse. All you have between the two is a three core wire.

 

[PRR]

me> I *think* the 2-contact NC NO plus a relay makes a clocked flipflop.

Korn and Korn, 1952:

 

[sahib]

Industry standard wiring for motor control with seperate on-off push buttons. One of the NO contacts on the contactor is used for latching but you need a series NC push button to break it. Hence two push buttons.  I think Shabtek wants to use a single button to turn on/off.

There is a reason for that type of wiring. There is additional NC contact of thermic relay in series to the latching circuit so that in case of the load exceeding the current rating the thermic relay contact opens and breaks the latch, turning the relay off to protect the load. Otherwise just have an on/off switch to control the relay.