How can I sense the position of a latching relay?

Other Hardware Home Automation
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We have pushbuttons and latching relays in our home. I can't take them out for reasons I won't go into. Also a latching relay saves energy when the load is 'on'.

I can trigger a 12v DC pulse with an Arduino to make them switch position from on to off and vice versa. They switch 230v ac up to 10 amps

But when the system boots up, I have no idea what position they are in and my dashboard is out of sync.

So I'm looking for a way to read the position of the relay into the Arduino as to keep the dash in sync.

Suggestions?

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Welcome to the forum

The relays presumably switch a voltage on and off. You could sense the voltage of the output which would give you the state of the relay

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Some latching relays have two or more sets of contacts. In such a case you can use an unused set to sense the state of the relay.

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Good call, but the voltage switched is 230v ac. I don't know how to safely do that.

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These do not. Good suggestion though!!

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I have no experience in the area, but you can sense the current in a wire without any contact with that wire

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There are two approaches. If the device draws current, you can safely use a current transformer around a current carrying wire to detect AC current flow. This won't work if the device is switched off locally. Introduction: CT Sensors - Interfacing with an Arduino — OpenEnergyMonitor 0.0.1 documentation

To detect voltage present at the relay output, you can use an AC optoisolator. Less safe.

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As a bit of a wild guess (as it's outside my field of knowledge), could you use a hall effect sensor attached to your relay case to detect the presence of a magnetic field when the relay coil is energised?

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I think that you will find a that a latching relay does not have a permanent magnetic field, even if it could be detected. As I understand it, the relay changes state each time it is energised and stays in the new state when the coil is no longer energised.

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True. There is a cog wheel inside that drives a wedge between two contacts. when the coil energizes, the cog turns a notch and removes the wedge. This close the contact and turns the load on. When power is removed from the coil, the cog stays in that position, keeping the load 'on'.
Then when energized again (momentarily) the cog turns a position again and puts the wedge back, breaking the contact. That switches the load off . This cycle repeats.
This means you do not keep the coil energized to keep a contact closed as in a traditional relay.

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This is the way.

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