I'm seeking help designing a circuit wherein we would have multiple 12 V DC signal inputs, with the goal of:
If one or more 12 V signals is ON, the main relay is energised and closed.
Basically, we have a vent fan that serves multiple appliances. When any appliance reaches a specified temperature, it sends out a continuous 12 VDC signal. This is intended to activate a relay to run a ventilation fan.
Because of the number of these appliances in use, we use one large fan, ducted to all appliances. We are manually switching the fan on and off at this time but I am aware of the 12 V heat-triggered output on each appliance and would like to take advantage of it (especially so the fan doesn't run all weekend when not needed).
What exceeds my knowledge is how to design the circuit with an "any or all" function, where either, any one 12 V signal by itself, or any number of 12 V signals at once, would turn on a relay.
(total # of collectively vented appliances, each with its own 12 V sender, is 7)
Each signal is sent via a two-wire DC lead (pos & neg).
Thanks in advance for any comments/thoughts.
Edit: the 12v signals need to be isolated from one another, so the most basic way I've thought of doing this is to have 7 "pilot" relays, one for each incoming 12v signal, and those relays would be switching a single "bus" 115v current that subsequently activates the main relay. But I am wondering if there's a better/more efficient design that would work.