3D Printed GPS Keychain Toy

A Child-Safe GPS Keychain Toy: designed to protect vulnerable schoolchildren in rural India

By Elin Simander, Aliyah Shah, Bora Muratoglu and Cansu Asya Gungordu.

BACKGROUND

In many rural and underprivileged regions of India, children are often required to walk long distances to school, sometimes along isolated highways or busy roads, without adult supervision. This is largely because parents are occupied with long working hours and physically demanding jobs, and schools are typically far from home. Unfortunately, these conditions leave children vulnerable to the threat of abduction or trafficking, especially in areas where communication and infrastructure are weak.

Families in these areas often face multiple barriers when it comes to protecting their children:

1. Economic limitations make it difficult to afford smartphones or GPS devices.
2. Low literacy levels mean parents might not understand the risks or how to use complex safety tools.
3. Poor mobile networks in rural areas make regular phone-based tracking unreliable.

PRODUCT

This project addresses these intersecting issues by designing a low-cost, discreet, child-friendly GPS-enabled safety device in the form of a keychain toy. The product achieves its intended purpose by:

Blending function with play: The device doubles as a rotating character toy, so children enjoy carrying it around without fear or stigma.

Offers an emergency alert system: When a child is in danger, pulling the hidden twist-and-pull safety pin sends their GPS coordinates to a nearby police station or guardian, enabling rapid response.

Is accessible and easy to use: No apps, no complicated buttons. Just a simple mechanical trigger.

Made to be culturally relatable: The rotating toy features cartoon characters inspired by popular Indian TV shows, helping children form a personal attachment to the object and reducing the chance of them losing it.

By integrating creative product design, simple electronics, and cultural sensitivity, this project aims to give families in high-risk areas a greater sense of security, empowerment, and connection. Without the need for high-tech knowledge or expensive gadgets.

The project is made for the course of Interactive Systems - Fabrication Lab, at Nuova Accademia di Belle Arti, Milano. Led by Professor Enrico Bassi.

3D printed parts (According to uploaded STL files)

1 GPS module (NEO-6M GPS Module: included in the specific microcontroller used in this project)

1 Microcontroller (Heltec Wireless Tracker - ESP32-based) LINK: https://amzn.eu/d/hnxGlFu

1 Rechargeable battery (Li-ion 3.7V Battery) LINK: https://amzn.eu/d/aq3yr0c

1 Micro Switch LINK: https://amzn.eu/d/ivEIMTa

1 2 mm screw

1 Jump loop keychain

Wires, solder/tape LINK: https://amzn.eu/d/b46Y46p

Print of cartoon characters on sticker paper

The first step is to 3D print the different parts of the toy.

The ''Spinning Part'' is to be printed 3 times, whilst the other ones are printed once.

There's minimal support material needed, and the printing times for each part is approximately:

BODY: 4 h 25 min

LID: 13 min

PIN: 14 min

SPINNING PART: 1 h 5 minutes (for a singular part)

The product was printed in white PLA (Polylactic Acid) using a WASP 2040 Turbo2 printer with FDM (Fused Deposition Modeling) technology. A 0.4 mm nozzle was used for the print.

All parts in .stl format are attached below.

To control the power going into the microcontroller, a simple switch connection is used:

Battery positive (red wire) → C (Common pin) on the switch

NC (Normally Closed) pin → 5V input of the microcontroller

Battery ground (black wire) → GND on the microcontroller

This means that when the switch is ON, the NC and C pins are connected, allowing current to flow into the 5V line, and the device turns on. When the switch is OFF, the circuit is broken, and the device stays off.

This setup allows the device a physical way to cut power to the system without unplugging anything, making it only activated when needed, which is ideal for power-saving and resetting.

When the pin is pulled out and the trigger is set off it, the activated code:

1. Connects to the GPS module using HardwareSerial. This means we open a second serial communication channel (other than the one used for debugging) to talk to the GPS chip, on pins 9 (RX) and 10 (TX).
2. It constantly listens for new GPS data from satellites.
3. We're using the TinyGPSPlus library to decode NMEA signals, which are basically the GPS messages that give us latitude and longitude.

When new location data is available, it:

1. Reads and saves the latitude and longitude values
2. Formats them into a ''human-readable string'' like: "Location: 41.123456, 29.123456"

Then, it uses the ''LoRa library'' to:

1. Begin a wireless LoRa packet
2. Print the location string into it
3. Send it to air (868 MHz)

All of this happens every few seconds. The loop() constantly waits for GPS updates and transmits them as soon as they arrive. In conclusion: The microcontroller powers on and runs the code as intended. The GPS module successfully locks onto a live signal and provides accurate location data. That information is then correctly formatted and transmitted over LoRa, which is fully functional.

In our prototype, we can’t see the message simply because there’s no receiver. The system is broadcasting data successfully, but nothing is listening, no police station, LoRa gateway, or second Heltec board. Still, the design proves the transmitter works. Used in real scenarios, the receiver could be a police base, a parent’s LoRa module, or a bridge forwarding data to an app.

The full code is attached below.

Four well-known Indian characters from children's books and TV shows are each divided into three parts, printed on A4 sticker paper, and then applied to the three 3D-printed spinning parts.

The characters are

1. Chutki - chhota bheem
2. Vir the robo
3. Little Sigham
4. Meena

The PDF for printing is attached below (A4).

The technical parts can be put into the body of the toy when completed and working, with the battery placed in the integrated battery-holder and the trigger by the opening for the pin. Then, it's time for assembly of all of the parts. Which is a very easy and comprehensive process.

1. Place all 3 spinning parts on the body in the correct order according to the stickers.
2. Slide in the lid and screw on the 2 mm screw.
3. Push in the pin until it's fully in, then turn it to stay in place.