tinket - bluetooth alarm

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
sdeemer
 
Posts: 1
Joined: Tue Jul 08, 2014 9:43 pm

tinket - bluetooth alarm

Post by sdeemer »

I would like to know all products needed to build an alarm that is set off if x feet from the primary object ... like if the alarm is placed in a book bag and the senor is in my pocket and I walk away 10 feet from the book bag the alarm goes off ...
can you supply me with this type of trinket - instructions and help so I may be able to build it myself ?
I like it if it can sync to a bluetooth device in the event the object is away from the bluetooth device ...
this way you never Forget your book bag or item left behind ..
as this is a learning tool for me I need any and all advice ...
any feedback even if it can not be done ...

User avatar
adafruit_support_mike
 
Posts: 67446
Joined: Thu Feb 11, 2010 2:51 pm

Re: tinket - bluetooth alarm

Post by adafruit_support_mike »

You'd probably want to use a sound-based system.

It's hard to measure distances between 10cm and 1km with electrical signals. The near-field effects like mutual capacitance and inductance drop almost to nothing, and the round-trip time of a radio wave is less than the time a signal spends moving through the circuit.

Sound moves at about 1000 feet per second though, so round-trip times over medium distances are measured in milliseconds. That's a fairly easy range to handle electrically.

In a two-part ranging system, one device emits a signal and the other device echoes it. It takes a certain amount of time for the signal to go from the first device to the second, so the echo will occur shortly after the original signal. It will take the same amount of time for the echo to go from the second back to the first, so the first device can simply measure the delay between emitting the signal and hearing the echo to calculate the distance to the second device.

To track multiple ranged devices, you give each device an ID and include the ID in the echo. That way the main device knows which device emitted each echo, or can tell a specific device to return an echo by putting the ID in the original signal.

Getting all that to work would be a medium-to-advanced level project.

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”