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BLE Transmitter+Receiver child locator? Answered

Hi, I'm not sure where to start, my understanding of the components and tech are minimal at best. I know what I want to achieve and I believe it is a possible project. I'm looking for any advice even if it exists outside of my current knowledge.

Essentially the idea is similar to this "lost child locator" product-  http://tinyurl.com/pd8goy7 or these t-shirts- http://tinyurl.com/mkm5b8k

What I'm struggling with is how to carry out the concept without involving a smart phone.

I'm looking for a larger range than 15M, multiple devices to respond to one-another, and for the watch to act as both transmitter and receiver. A simple LED indication is sufficient, no sound or vibration are necessary. I think BLE is the proper signal to work with but I don't want to involve smart phones at all. Compactness is a major plus, but ultimately I would settle for a mint tin or puck sized device. Everything would need to run on a small battery as well.

The practical application of this project is for times when you're in a large crowd and you are looking for your group. If you had a watch tuned to your group, you could more easily track each other down if you knew someone was close. 


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5 years ago

Not really doable.The first link is a transmitter and receiver. When the transmitter gets too far away the receiver looses signal and sounds an alarm. The shirts use some sort of proximity detection similar to the first.

To use radio tracking you will need a good directional antenna which would be way larger than what you are looking for. You've probably seen nature shows where they are holding a large antenna trying to locate an animal with a radio tracker on it. While the transmitter and receiver are relatively small you still need a rather large antenna to find the direction the signal is coming from. One that you have to swing around till you get a lock on the direction. Nothing small enough to fit in a mint tin could give you direction to the strongest signal source.

Now days systems are smaller and use GPS. Such as this one for dogs.


The small black part is the GPS antenna. The larger part holds the batteries and the radio transmitter that sends the dog's GPS coordinates to the receiver. The receiver has the radio receiver in it as well as a GPS so it can take those GPS coordinates, plot it on a map and show your location on the map relative to the collars.

A similar system can be built without as many features to help reduce the size of the receiver/tracker unit. but it won't get small enough to be in a watch or a mint tin. Especially if the system also needs to transmit it's location.

The simplest and most compact option for a system like your looking for is a bunch of smart phones with a tracking and reporting app running on them. Even better. Considering your talking large group and maybe including kids. So go buy a bunch of cheap burner phones. You know the ones that require no plan. All you gotta do is buy cards to get minutes. Everyone gets a cheap $40 phone with $20 worth of minutes on it. Need to find someone. Give them a call. Phones stay in a stash for future outings and you add minutes as needed.