A good sensor for a Bed Occupied detector?

Question

I'm trying to build a presence sensor for my bed, to help trigger assorted home automation functions.

My first thought was to use a FSR and place it between the frame and boxsprings. I know how to deal with the A2D bit. However, I can't find one with a broad enough weight range.

Given that it's a heavy bed (not sure exactly how heavy), I was hoping to find something with a range of 0-1000 pounds with a calibrated accuracy of 100 pounds.

Can anyone suggest an appropriate sensor, or another approach?

Answer 1

I am aware this question is fairly old at the moment but it is an interesting idea. My initial thought was simply some form of heat sensor however on searching i can imagine lying on one to be somewhat uncomfortable. then i came across this little number. Slip one of these under the sheets and wire it up with some ow profile wires and your sorted. Depending on the bed style you may even be able to place this under the matress if the frame flexes a bit when someone is on it.

Flex Sensor 2.2"

A simple flex sensor 2.2" in length. As the sensor is flexed, the resistance across the >sensor increases. Patented technology by Spectra Symbol - they claim these sensors were >used in the original Nintendo Power Glove.

The resistance of the flex sensor changes when the metal pads are on the outside of the >bend (text on inside of bend).

Connector is 0.1" spaced and bread board friendly. Check datasheet for full >specifications.

http://www.hobbytronics.co.uk/sensors/temp-pressure/flex-sensor-2-2

Answer 2

Just to follow up (way, way later), I eventually bought one of these sensors, and attached it to the bottom of the wooden frame of the bed.

http://www.sureaction.com/pulsor_stress_sensor.html (The ENHP version, though I forget the difference).

I have device (used a Particle Photon instead of Raspberry Pi, but either would work) checking the sensor for changes in it's resistance to decide if the bed is occupied or not. The trickiest part of the logic is that the sensor will slowly drift from shifting temperature and humidity which can throw the calibration way off.