I need to control a bi-stable relay with 2 SPDT latching switches

Question

I'm a mech engineer trying to use 2 vandal resistant, SPDT, latching switches to control a power distribution module. The module has an internal bi-stable relay to turn the outputs on and off. The trigger wire for the module is fed 12v to turn on and then turns off when grounded. I need to use 2 switches for activation (1 inside the vehicle, 1 outside) and don't want to use rocker switches (although i wouldn't be asking this question if i did).

My current setup is using the 2 latching vandal switches in a conventional 3-way setup which works fine to activate the module but i can't figure out how to get the circuit to pull down the trigger to ground when I want to shut it off. I was thinking a motor reversing circuit with relays but was hoping for a simpler, and more space saving solution. Any suggestions would be great.

Here's the datasheet for the module that shows the recommended control wiring: https://www.littelfuse.com/media?resourcetype=datasheets&itemid=99c7c610-ef0f-487c-a3ff-aa85e05d47be&filename=sl-series-pdm-datasheet

Answer 1

The simplest way is probably to use an SPDT relay controlled by the switches in the same way you'd control a two-way light:

^{simulate this circuit – Schematic created using CircuitLab}

The downside is that the relay will be powered whenever you want the output to be powered, so you need to use one with low enough current consumption not to add too much extra drain on the battery.

To design an electronic version that could use less power than a relay, you'd need to know how much current the trigger input needed to work. I can't see that information in the datasheet so it would be a question for the manufacturer.