Reversed motion sensor

El_Watcher · 10 Mar 2016 at 12:30

I have a project I am looking into, which requires a motion sensor to detect when someone approaches. Normally with motion sensors, it detects someone and turns lights on, but what I need it to do is to detect someone and turn something off (not the lights by the way

).

Does anyone know of a motion sensor which can work in this reversed manner?
Or know how to wire up a standard detector to work like this and what other components are needed?

(This will all be at mains 220-230Vac)

Delvis · 10 Mar 2016 at 12:31

In the sense of a light switch surely it's just a reversed motion? What are you trying to turn off?

Gilly · 10 Mar 2016 at 12:32

Reverse the wires going to the switch

[/colourblind noob who stays away from lecktrickery]

Mr_Orange · 10 Mar 2016 at 12:35

Look for a normally closed occupancy switch or wire a standard occupancy switch to a normally closed contactor/relay.

Edit: Talk to your local electrical wholesaler for advice on specific products

Edit 2: It might be worth contacting a company called Danlers

Luke · 10 Mar 2016 at 12:52

There has to be a better way to turn off your machine gun home defence turrets?

Renton · 10 Mar 2016 at 12:55

Just connect the sensor to a relay of the same control voltage of its output.
The relay will have N/O normally open and N/C normally closed outputs so when the sensor actuates the N/C relay output will open so if you connect to this your switch will essentially go off

Make sense?

El_Watcher · 10 Mar 2016 at 13:01

Mr_Orange said:
Look for a normally closed occupancy switch or wire a standard occupancy switch to a normally closed contactor/relay.

Edit: Talk to your local electrical wholesaler for advice on specific products

Edit 2: It might be worth contacting a company called Danlers

Thanks for that info, will have a look.

I have just found this project which uses an Arduino board to control an SSR. The code used looks like it could be easily reversed so motion sets the control variable low rather than high.

Renton said:
Just connect the sensor to a relay of the same control voltage of its output.
The relay will have N/O normally open and N/C normally closed outputs so when the sensor actuates the N/C relay output will open so if you connect to this your switch will essentially go off

Make sense?

I think so, although I will look into relays a bit more. Thanks.

Mynight · 10 Mar 2016 at 13:03

^^ that's what I'd do(rentons).

Also I note a search on the subject brings up an awful lot of cannabis horticulturist enthusiast websites

. Are you trying to protect your ahem vegetables?

El_Watcher · 10 Mar 2016 at 14:22

Mynight said:
^^ that's what I'd do(rentons).

Also I note a search on the subject brings up an awful lot of cannabis horticulturist enthusiast websites . Are you trying to protect your ahem vegetables?

No vegetables were involved in this project, except maybe my boss for asking at such short notice

Diddums · 10 Mar 2016 at 14:28

You need a 240v latching break relay (or whatever it's called). This will complete the circuit provided there's no power to it, and break the circuit when energized. The energy will come from the motion sensor so when it detects motion, it'll energize the relay and interrupt the circuit.

I'll ask some of the sparkies here, I'm sure they'll know this better than me.