i have a bracelect project for geolocation and i add the geofencing to my project and i want to add another option it's get notification in phone or call when the bracelet is take off from the hand, what's the component that i will use to know if the bracelet it taken off or not ?
What is the process of taking the bracelet off? Does it have a clasp, or is it elastic?
Temperature sensor in the bracelet may do (unless your local air temperature is at body temperature, like it has been for us for the past two weeks... then you won't detect it until evening).
it's elastic bracelet, and until now i develope it just in bread board i don't did a design for the bracelet
You might do some experimentation with capacitive sensing. There's some pretty good information and a library here:
https://www.pjrc.com/teensy/td_libs_CapacitiveSensor.html
That's Paul Stoffregen's (the creator the the Teensy) website so it has a Teensy focus but the library and the information will also be usable with a regular Arduino or your own custom board.
This seems a bit discouraging:
Teensy's ground pin should be connected to earth ground for best results. Normally the USB cable connects to a PC, which connects to earth ground by its power code. But when using a laptop on battery power or running without a computer, you may need to make a dedicated connection to earth ground.
I think you'd definitely need to add some "smarts" to your code. Likely you will not be able to rely on stable readings but I think there will be a significant change in capacitance between the sensor being in close proximity to a wrist and not.
Other ideas are:
- Light sensor - this wouldn't work if the bracelet was taken off in the dark.
- Pressure sensor - this will require the bracelet to be tight against the skin, which might be uncomfortable.
Another possibility is making the band or incorporating into the band a "stretch sensor". Something like this:
That stuff is also available from other sources but Adafruit gives a good overview.
You can also get conductive Lycra fabric that will work in a similar way (increases resistance when stretched) that might be more suitable for a bracelet.