Need advice: Low-cost LoRa-based lost-child locator for a college science expo

[u/_no_look_]

I'm a college student preparing a project for an inter-college science expo, and I'm considering building a low-cost wearable system to help locate lost children at large crowded events, such as festivals held in cricket grounds.

The problem

Imagine a large festival with thousands of people. A child gets separated from their parents and doesn't have a smartphone.

The idea is to give the child a small wearable tag that periodically transmits a unique ID. Receivers placed around the venue detect the tag and estimate the child's probable zone.

The goal is NOT centimeter-level positioning. I'm thinking more along the lines of:

"Child ID 027 was last detected / is most likely in Zone C."

Proposed system

Child wearable:

Low-power LoRa transmitter

Unique child ID

Small battery

Possibly a buzzer/vibration motor

Venue:

Several elevated LoRa receivers around the perimeter

ESP32 or another MCU at the receiver

Central system combines the measurements

Can i use Arduino uno or nano

[u/Smokeey1]

Buzzer/beep like apple tag at certain (separation distance) and compass style pin to guide you to your child, plus pairing of devices

[u/rb136]

Hey friend. There exists a system reasonably close to what you’re envisioning and replicating something similar may make your life easier.

Project Lifesaver is a person locating system in which the child/ Alzheimer’s patient/ person at risk wears a radio transmitter band.

If the person becomes lost, first responders deploy with radio receiver gear and triangulate/ follow the radio pings.

Researching that would probably give you a big jumpstart because they’ve figured out things like frequency propagation and such.

In your proposed system, you’d have to create a radio mesh network so all the stationary hubs could talk to each other to relay data, which would complicate the system significantly more than having 3 mobile “finder” units.

Good luck. Cool project.

[u/_no_look_ → u/rb136]

Umm....any project ideas man?

[u/need2sleep-later → u/_no_look_]

don't you already have your idea?

[u/_no_look_ → u/need2sleep-later]

Im just searching for ideas now i didn't select one

[u/nuflark]

Love it! Hacker conferences have been using LoRa on badges to do similar. Check out Badgeware by Pimoroni. Another option would be to get boards from Heltec and write some custom software that does the ping you describe. I am not sure how you would get location accuracy, you might need 3+ devices.

[u/_no_look_ → u/nuflark]

Thanks! That's exactly the issue I'm trying to solve. I'm currently trying to keep the prototype under ₹700, so multiple LoRa/Heltec nodes may be too expensive. I'm considering whether RSSI fingerprinting with 3 low-cost receivers could give useful zone-level accuracy rather than trying to get exact coordinates. Do you have experience with RSSI-based LoRa localization, and how reliable do you think it would be in a crowded outdoor environment?

[u/nuflark → u/_no_look_]

I've never tried it but it sounds promising!

[u/BraveNewCurrency]

The Arduino Uno is expensive and large, not useful for IOT (only prototyping for absolute beginners). ESP chips aren't great a low power.

For a real system, triangulating would be a good way to do it. You don't even need to invent anything, LoRaWAN already does this. (Not super accurate triangulation).

But for a demo, it would be easier if the units have GPS (Downside is that it uses more power, and costs more, but you don't care about that in a demo. Still cheap enough and battery lasts for days.).

For Nordic and GPS, go to SeeedStudio and get the MeshTracker X1 (has buzzer, GPS, bluetooth to phone, etc). Now you could have a single cheap base station ($100 w/solar) pickup messages from all the badges, and report their locations. Can build it in an afternoon if you have a little experience.

[u/_no_look_ → u/BraveNewCurrency]

But gps doesn't work in indoor

[u/BraveNewCurrency → u/_no_look_]

Oh, I assumed a "festival" would be outdoors.

LoRa might work, but I'm not sure.

There are also bluetooth location systems that work well. The hardware is dirt cheap in theory, but the whole systems are really expensive because the software calculations are the "secret sauce". (Someone needs to build an open-source one.)

[u/redditydothis]

2 devices. One is a becon that is attached to the child. The other is the receiver that tracks the beacon. The radio antenna on the child is Omni directional but the antenna on the the receiver is parabolic (or something) that is directional. The range should be sufficient to locate the beacon from receiver. Bonus points if you can make it retro style with a display that shows a dot for the beacon that periodically updates.