Miniature 4G Kids Phone, a ESP32 project

This guide walks through building a miniature 4G kids phone prototype based on the ESP32 microcontroller. The project demonstrates basic button input handling and LED status indicators, providing a foundation for understanding how physical controls and feedback work in embedded systems.

Following this guide, builders will receive a wiring diagram showing how to connect two tactile buttons and two LEDs to the ESP32, a complete parts list, and firmware that debounces button presses and controls the indicator lights. Assembly takes just a few minutes and requires only basic soldering skills.

Wiring diagram

Gather all the parts

Qty	Component
1	Owned normally-open tactile button Owned normally-open tactile button Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Owned normally-open tactile button Owned normally-open tactile button Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Owned green LED Owned green LED Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Owned red LED Owned red LED Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Series resistor 2.2 kohm Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Series resistor 2.2 kohm Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Button pull-up resistor 10 kohm Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.
1	Button pull-up resistor 10 kohm Revision B controller validation sheet only; see design/README.md for unreleased phone circuitry.

Assemble it in 3 steps

1. Review the unreleased phone design

Read data/design/README.md. Only the USB-powered button and LED validation circuit is released here. Do not connect the battery, charger, boost converter or modem to this validation circuit.

The phone power and audio design is not released for assembly or child use.

2. Connect the two buttons

Connect MAMA between D1 (GPIO3) and ground, and TATA between D2 (GPIO4) and ground. Add one 10 kohm resistor from each button signal to 3V3. Use two electrically distinct switch contacts.

3. Connect the indicators

D4 (GPIO6) connects through its 2.2 kohm resistor to the green LED anode. D5 (GPIO7) connects through its separate 2.2 kohm resistor to the red LED anode. Both cathodes go to ground. Red stays on to indicate this is not phone firmware; green lights when a button is pressed.

Review all connections

1. Connections between "sw_mama" and "ESP32"

Function	sw_mama	ESP32
`data`	1	GPIO 3
`ground`	2	GND

2. Connections between "sw_tata" and "ESP32"

Function	sw_tata	ESP32
`data`	1	GPIO 4
`ground`	2	GND

3. Connections between "r_mama" and "ESP32"

Function	r_mama	ESP32
`power`	1	3V3
`data`	2 → Owned normally-open tactile button 1	EXT

4. Connections between "r_tata" and "ESP32"

Function	r_tata	ESP32
`power`	1	3V3
`data`	2 → Owned normally-open tactile button 1	EXT

5. Connections between "r_green" and "ESP32"

Function	r_green	ESP32
`data`	1	GPIO 6
`data`	2 → Owned green LED A	EXT

6. Connections between "led_green" and "ESP32"

Function	led_green	ESP32
`ground`	K	GND

7. Connections between "r_red" and "ESP32"

Function	r_red	ESP32
`data`	1	GPIO 7
`data`	2 → Owned red LED A	EXT

8. Connections between "led_red" and "ESP32"

Function	led_red	ESP32
`ground`	K	GND

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>
// UI validation ONLY. No modem control or phone functionality is implemented.
// Green lights only while a button is held: it does NOT report network readiness.
constexpr int MAMA=3,TATA=4,GREEN=6,RED=7;
void setup(){pinMode(MAMA,INPUT);pinMode(TATA,INPUT);pinMode(GREEN,OUTPUT);pinMode(RED,OUTPUT);digitalWrite(RED,HIGH);}
void loop(){ static uint32_t changed=0; static bool previous=false,stable=false;
 bool pressed=!digitalRead(MAMA)||!digitalRead(TATA);
 if(pressed!=previous){previous=pressed;changed=millis();}
 if(millis()-changed>=30)stable=pressed;
 digitalWrite(GREEN,stable); delay(5);
}