SparkFun Forums

[ldickson]

I honestly dont know what to call this project so please dont judge. I have been looking around but no one has made something like this before that I have found anyways.
I am working to make a "necklace", the term refers to it being hung from the neck via a material that hasnt been decided yet, and that is paired to another on and glows when the two get within 5km(3miles) of eachother including through walls and what not. The purpose is that they will light up an LED bar graph the closer they get to each other.

I will be using a Arduino Pro Mini 328 5v as the controller to read the signal and to run the led bar graph which which will have preprogrammed low power and powersaving modes to conserve power and extend time between charges. My end goal is to make it able to last at least 3 days before needing to charge.

Anyone have any ideas for what type of transceiver to use that will give me the range and still give me the battery life?

[leon_heller]

What frequencies are you authorised to use?

Where will the antennae be mounted?

[jremington]

It is not possible for us hobbyists to measure distances using radio, and transmitters take a lot of power. This is a totally unrealistic project.

[ldickson]

I am authorized to use 135.7 khz to 250.000 GHz operating frequencies here in Canada. As for the signal it doesnt need to be a strong one, nor use much bandwith just enough to be able to read the strength of it. The antenna can be one of many things, it could be the metallic casing for it (though I had planned on using that as a ground) could be internal or it could be the means of attaching it to the neck, I can get a wire turned into an antenna and get it tuned to any frequency needed.

I should point out that the first take of it will be using an APC220 Wireless RF Module, for my testing. I was hoping for input for other means of a transceiver.

I am just hoping I didnt have to use ham radio frequencies or to have to licence a frequency for my use.

[leon_heller]

You obviously don't have a clue about designing such a system, don't waste any more time on it.

[ldickson]

Dont I? Using a XBee Pro 900 RPSMA with a 900MHz Duck Antenna RP-SMA i can theoretically I can get between 1km and 5km depending on interference and LOS range. Using sleep modes and high capacity lithium batteries and powersaver modes on the arduino I can get about 24 hours depending on current draw of the LED's and how often I have it turn on the xbee, I could extend it longer

[ratsept]

Some of the LORA series chips from Semtech have some impressive numbers quoted in their datasheets. Mind you I've never tried one myself but according to their datasheets some parts have a link budget of over 160 dB. You could try some of these. They can probably be activated for only brief pulses and when a signal is found switch to a higher sampling rate. The receiver side would need to be constantly powered though unless you find a way to synchronize the devices clocks enough. After an initial contact is made two devices can synchronize and the receiver can predict when it needs to turn on just before the transmitter starts. For ranging in urban environments especially RSSI is not going to be very precise. And time-of-flight is probably not possible with these modules. Since they use some kind of spread-spectrum technology they should be a bit more resistant to multipath fading and other problems in narrow-band systems but, again, I haven't tried them so I couldn't say for sure.

[ratsept]

Actually this could be done very easily and over almost any distance. Just build two necklaces with BLE radios. Make an app that publishes your phones GPS position to some datasource that the other persons phone can access too (data.sparkfun.com?). Do the same thing on the other persons phone and make both phones calculate the distance to the other. Now connect phones to necklaces over BLE and write the distance to a custom characteristic. Simple and can be extended to any range. I'm sure whoever wants/has such a necklace also has a smartphone and at least in my country GPS and cellular data coverage is pretty universal. Plus this would easily last 3 days depending on your led use and battery.