Need help finding a weight sensing on/off switch? Like in lawn mowers.

[ben.wins]

So I'm working on a project that hinges on a device being turned on when a person sits in a seat, and then off when the stand. What I need it to do is take a 12V power supply and only complete the circuit when a person is seated. Does this kind of sensor have a name or does anyone have any recommendations? It's kind of like a reverse deadman switch, and I think they're called force sensors but I'm having trouble finding one that simply completes the circuit instead of outputting information.

 

[Minder]

You wouldn't want to go to the extent of a load cell for that operation, unless you wanted to weigh the person.
I would use a either a simple reed switch and magnet to detect when a weight is placed on the seat, or a small prox switch such as Honeywell SS400 series and a miniature magnet,
You would need some kind of simple pressure/sense mechanism that physically moves down very slightly when sat on then return up, a small coil spring could do it.
Even a simple limit switch will do the same.
M

 

[Alec_t]

Welcome to EP!
You're looking for a 'seat occupancy sensor'. But the type used in a car seat is expensive.!
A coil spring (as Minder suggested) or leaf spring, operating a lever-actuated microswitch, would be my choice.

 

[Sunnysky]

If the seat has no springs, this can be a mechanical challenge.
An optical reflector thru hole in the seat might work powered by ignition switch.

 

[Herschel Peeler]

So I'm working on a project that hinges on a device being turned on when a person sits in a seat, and then off when the stand. What I need it to do is take a 12V power supply and only complete the circuit when a person is seated. Does this kind of sensor have a name or does anyone have any recommendations? It's kind of like a reverse deadman switch, and I think they're called force sensors but I'm having trouble finding one that simply completes the circuit instead of outputting information.

http://www.jameco.com/z/1696-Pololu-1-2-Inch-Circular-Force-Sensing-Resistor_2128260.html

Pressure sensitive resistor, distributed by Jameco Electronics. They come in different sizes and shapes. Maybe put a marble on top of it and a piece of cardboard, or something.

 

[duke37]

Fit a microswitch under the seat with a rod to activate it through a hole in the seat.