Raspberry Pi Forums

I'm trying to design an alert system for a handicapped child that lives nearby me where the system will send an alert via SMS to their mother when the child gets too far from the house, and another when they re-enter the area. I assume and RF signal would be the best for that. My question is: Where can I find one reliable enough that it could detect distance of up to... let's say 150-200 ft. that could be calibrated to plus or minus 10 ft. or so? If you know which pins go where that would be helpful as well seeing as I've never worked with anything external before. Only the command terminal of the OS.

If you have a better idea for a sensor please let me know. It's for a handicapped 3 year old who figured out how to open doors, but can't communicate or reason well.

We're also looking into other options but I figured this one would be interesting for me to try.

Thanks for any info in advance!

Also is higher frequency better for wall penetration or lower? I see some 315Mhz and 433Mhz on Amazon for 5 bucks.

These transmitters and receiver modules you're referring to are basic in nature so you need to implement your own communication protocol.
As for 315MHz and 433MHz they do not have any benefit for range or penetration, however like all radios for optimum operation you need the correct antenna length - http://wb5mrn.com/ham/antenna.htm which would be a quarter wave dipole / whip for a piece of wire.
In some counties it's illegal to operator a radio transmitter on certain frequencies for example 315MHz is not a legal in the UK.
This is one of the reasons why these boards offer different operating frequencies apart from avoiding interference from other similar devices.

Richard S.

I would have thought calibrating to that accuracy would be tricky as radio is affected by all sorts of things like weather. My first point of contact for all things radio would be Ciseco (http://shop.ciseco.co.uk/), they are really knowledgeable and friendly. You might want to look at some of the bluetooth proximity projects, possibly not the range you need though.

Depending on number of doors , amount of people in the house etc. an alternative approach could be a camera and motion detection software, lots of projects documented here, but this springs to mind; http://www.raspberrypi.org/archives/5071

Good luck!

Gordon

Perhaps another approach would be GPS and an audible alarm? Might be disconcerting for the child...

GordonTGopher wrote:You might want to look at some of the bluetooth proximity projects, possibly not the range you need though.

No, bluetooth doesn't have the range nor does it go through walls well. I already considered that.

GordonTGopher wrote:Depending on number of doors , amount of people in the house etc. an alternative approach could be a camera and motion detection software...

The motion detection idea was good, but how do you distinguish between the handicapped child and the other children going out to play? Or visitors coming in? Or the father going to work? We need to know when the one child leaves.

Douglas6 wrote:Perhaps another approach would be GPS and an audible alarm? Might be disconcerting for the child...

I've never worked with GPS before... Could I set up a 2nd device like a Pi or computer to track her and alert her mom when she leaves bounries?

TheGreatGizmo wrote:detect distance of up to... let's say 150-200 ft. that could be calibrated to plus or minus 10 ft. or so

I've realized it doesn't need to know exactly how far away she is. Only when she gets a certain distance away. So even if it doesn't have a +/- 10 ft detection even if it's +/- 50 ft. that would give us warning before she could get too far away. All we need to know is if she leaves the house.

TheGreatGizmo wrote:

Douglas6 wrote:Perhaps another approach would be GPS and an audible alarm? Might be disconcerting for the child...

I've never worked with GPS before... Could I set up a 2nd device like a Pi or computer to track her and alert her mom when she leaves bounries?

You'd be left with the problem of communicating between the mobile unit and home base, probably either RF, Wifi, or Bluetooth. Sound waves are a time-honored method, but probably not ideal in this case.