How to detect touch without mechanical triggers?

[ric_vas]

Detect touch

I need to substitute a mechanical trigger used inside a suit case handler (metal handler). The trigger (coil and switch) is used to detect someone is carrying the suit case. The idea is to remove the mechanical items and have something based on touch only. I was thinking about using the metallic handle as a capacitive sensor and somehow process the signal. However I need to know if more than on person are handling it at the same time. Any tip?

Thanks in advance.

Ric

 

[kender]

Re: Detect touch

I was thinking about using the metallic handle as a capacitive sensor and somehow process the signal.

Capacitive sensors work well for sensing touch. Just in case, here are some application notes for capacitive sensors.
Principles of operation http://www.capsense.com/capsense-wp.pdf
Write-up on capacitive touch sensors http://www.analog.com/library/analogDialogue/archives/40-10/cap_sensors.html
Maxim App Note 1903. Capacitive proximity detector. **broken link removed**

However I need to know if more than on person are handling it at the same time.

People are very different in their physical parameters. Your case could be handled by 2 girls weighing 60kg each or by 1 man weighing 120kg. Same goes for body capacitance and skin impedance. The latter can vary 2 orders of magnitude. IMHO, it's almost impossible to detect reliably the number of people through one capacitive measurement. You could post your question to this group: **broken link removed**. There's a good number of sensor experts, who like tough problems

 

[ric_vas]

Re: Detect touch

Kender,

Thanks for pointing me to some AN...that will be very helpful for sure. As far the second part I just can´t see how to make it happen. Even with the mechanical trigger there was a problem...the solution at that time was to create a sort of obstacle so that just one hand fit in at time, but that´s no feasible anymore (design issue).

I´ll keep researching it....

Ric