arduino capacitive sensor

I've had great success using an arduino as a capacitive sensor, as described here:

I'm trying to expand that idea to create a series of in-floor (under my carpet) sensors throughout a room. The above method does not work for that, as the ability to "sense" capacitance apparently degrades when I increase the length of the lead running from the arduino to the end point of the sensor (the bit with tinfoil attached) to more than a meter or so.

Basically the idea is: using a series of sensors placed under the carpet I'd like to be able to track a persons movement throughout a room.

Would an inductive sensor work better, and if so, any advice on implementing it with an arduino?

I'm definitely not an electronics geek, just having some fun here.


i dont think an inductive sensor would work at all. needs more metal to sense

Did you use shielded wire for the connections to the sensor? Regular insulated wire will act like an antenna, which would explain the sensitivity issue.

However, I think you'd be better off trying to do something like a "giant keypad" to sense position like that. Or even hack up a Dance Dance Revolution mat. There's lots of solutions.

id you use shielded wire for the connections to the sensor?

Using shielded wire is not much better because it has a high capacitance, this means that the changes you see at the sensor end are swamped by this fixed value.

Capacitive sensors are only any good when the measuring device is close to the sensor. Single coil inductive sensors only sense metal. Three coil sensors can be set up to detect the water in people but again the electronics need to be close to the coils.

You are probably better off with a pressure sensor switch used in alarm systems, these are large and cheap.

Thanks for the replies. I've gone with the pressure sensor route. I was able to piece together several pressure sensors using a conductive packaging foam I picked up cheap at office depot, and some window screen from my garage. The idea came from here: It took a lot of tweaking, but it's working like a charm.