14. Networking and communications

I have used deepseek to help me with the documentation and the code for external based on what I already did on the previous weeks. Deepseek

Group Assignment

In my team, we used 3 ESP32-C3 microcontrollers to demonstrate ESP-NOW protocol communication. We configured one device as the master and two devices as slaves. The master ESP32-C3 broadcasts messages to both slave devices simultaneously using ESP-NOW’s peer-to-peer architecture.

This setup demonstrates: - Direct device-to-device communication without WiFi router - Low-latency wireless messaging using MAC address routing - One-to-many topology where a single sender reaches multiple receivers

Group Work Page

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Individual Assignment

Objective

This week, I established Bluetooth Low Energy (BLE) communication between my ESP32-C3 microcontroller and my smartphone. The goal was to wirelessly control an LED on the ESP32-C3 using a BLE scanner app on my phone.

Communication Flow:

Direction	Data	Purpose
Phone → ESP32	“1”	Turn LED ON
Phone → ESP32	“0”	Turn LED OFF

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Setup

Hardware

I received a new ESP32-C3 microcontroller from Fab Lab Oulu. I soldered legs for it in oder to connect it to my board.

Software

1. Arduino IDE Configuration

I started by configuring the Arduino IDE to support my ESP32-C3 board:

• Install ESP32 board support via Boards Manager
• Select the correct board: XIAO ESP32C3 (or generic ESP32-C3)
• Choose the appropriate COM port

Board Selection:

2. BLE Scanner App

To communicate with the ESP32-C3 from my phone, I installed a BLE Scanner application. This app allows me to: - Discover nearby BLE devices - Connect to advertising peripherals - Write values to characteristics

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Code Implementation

Source

I started with an example from the weekly material on Moodle. The complete code is available on GitHub: ESP32-C3 Bluetooth Communication Example

Example Reference:

Code Fixes Needed

During the setup, the example code from GitHub contained several syntax errors and compatibility issues with the XIAO ESP32-C3 environment. Below are the specific problems I encountered and how I resolved them.

Issue 1: Syntax Errors in BLE Callback Class

The original code had typos and incorrect data types in the BLE callback class, which prevented successful compilation.

Before Fix:

Problems Identified:

Problem	Explanation
std::string cmd	While technically correct, String is preferred for Arduino compatibility.

After Fix:

Code Explanation

Code Section	Purpose
#include <BLEDevice.h> etc.	Include BLE libraries
#define SERVICE_UUID	Unique identifier for BLE service
#define RX_UUID	Characteristic for receiving data (Phone → ESP32)
#define LED_PIN D6	Define LED pin on XIAO ESP32-C3
ServerCallbacks class	Handles connection/disconnection events
RXCallbacks class	Handles incoming data - turns LED ON/OFF
BLEDevice::init("XIAO_C3_BLE")	Advertise device with this name
rxCharacteristic->setCallbacks()	Register callback for incoming data

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Compilation and Upload

Compiling the Code

The code compiled successfully with no errors.

Serial Monitor Output

After uploading, the Serial Monitor displayed:

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Connecting via BLE Scanner

Step 1: Discover the Device

After successfully uploading the code, I opened the BLE Scanner app on my phone. The app detected my microcontroller advertising as XIAO_C3_BLE.

Step 2: Establish Connection

I tapped the connect button next to “XIAO_C3_BLE”. The app established a BLE connection and displayed detailed information about the device.

What the app shows: - Service UUID: 6E400001-B5A3-F393-E0A9-E50E24DCCA9E - RX Characteristic (Write): Used to send LED commands

Step 3: Send LED Commands

The app provided a text field where I could write values to the RX characteristic.

Command protocol:

Write Value	LED Action
“1”	Turns ON
“0”	Turns OFF

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Troubleshooting: LED Not Responding

The Problem

After writing values to the BLE characteristic, the LED did not change state. The Serial Monitor showed that values were being received, but the physical LED remained off.

Root Cause

The original example code used 8 as the pin reference. However, on the XIAO ESP32-C3, 8 is not defined. My board uses D6 (GPIO6) for the LED.

Incorrect pin configuration:

The Fix

I modified the code to explicitly define the correct LED pin:

// Before (incorrect)
#define LED_PIN 8

// After (correct)
#define LED_PIN D6 

Result

After recompiling, re-uploading, and reconnecting, the LED responded perfectly to the BLE commands.

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Testing Results

Test	Action	Expected Result	Actual Result
1	Send “1” via BLE	LED turns ON	Passed
2	Send “0” via BLE	LED turns OFF	Passed
4	Disconnect/reconnect	Reconnection successful	Passed

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Extension: BLE Control of NeoPixel LEDs

After successfully controlling a single LED via BLE, I extended the project to control multiple NeoPixel LEDs using the same BLE connection. Instead of just ON/OFF, I can now send numbers from my phone to light up a specific number of red LEDs.

How it works:

BLE Command	Action
Send “0”	All LEDs OFF
Send “1”	LED 1 ON (red)
Send “2”	LEDs 1-2 ON (red)
Send “3”	LEDs 1-3 ON (red)
Send “4”	LEDs 1-4 ON (red)
Send “5”	LEDs 1-5 ON (red)

Code Added:

#include <Adafruit_NeoPixel.h>

#define NEOPIXEL_PIN D10      // GPIO12 - NeoPixel data pin
#define NUM_PIXELS 5          // Number of NeoPixels

Adafruit_NeoPixel pixel(NUM_PIXELS, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);

// Inside RXCallbacks::onWrite():
int ledCount = value.toInt();
if (ledCount > NUM_PIXELS) ledCount = NUM_PIXELS;
if (ledCount < 0) ledCount = 0;

// Turn all OFF first
for(int i = 0; i < NUM_PIXELS; i++) {
  pixel.setPixelColor(i, pixel.Color(0, 0, 0));
}
// Turn ON requested number in RED
for(int i = 0; i < ledCount; i++) {
  pixel.setPixelColor(i, pixel.Color(255, 0, 0));
}
pixel.show();

Testing Result:

When I sent “3” from the BLE Scanner app, the first 3 NeoPixel LEDs turned red. When I sent “4”, the first 4 NeoPixel LEDs turned red. The ESP32 responded instantly with no noticeable delay.

What I learned from this extension:

Concept	What I Learned
Data Parsing	Converting BLE string input to integer for LED count
Scalability	The same BLE principle works for controlling any number of LEDs

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Key Learnings

Concept	What I Learned
BLE Architecture	BLE uses Service/Characteristic hierarchy with unique UUID identifiers
RX Characteristic	Write property allows phone to send commands to ESP32
Callback-Driven Programming	onWrite() handles incoming data automatically without polling
Nordic UART Service (NUS)	Standard UUIDs make ESP32 compatible with existing BLE apps
Serial Debugging	Serial Monitor is essential for confirming data reception

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Files

File	Description
BLE_connection.ino	BLE LED control
BLE_Neopixel.ino	BLE NeoPixel control

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Reflection

This assignment gave me practical experience with Bluetooth Low Energy communication on the ESP32-C3 platform. Key takeaways:

1. Simple Control: The system successfully receives “1” and “0” commands from my phone to turn an LED ON and OFF wirelessly.

2. BLE Architecture Understanding: Learning about Services, Characteristics, and UUIDs was essential. The RX characteristic with WRITE property is what enables phone-to-ESP32 communication.

3. Callback-Based Programming: BLE uses asynchronous callbacks (onWrite()) rather than polling loops. This is efficient because the ESP32 can sleep or do other tasks while waiting for commands.

4. Serial Debugging: Serial Monitor was invaluable for confirming that data was being received correctly before debugging the LED hardware.

The combination of the group assignment (ESP-NOW for device-to-device) and individual assignment (BLE for phone integration) gave me a comprehensive understanding of wireless communication options for embedded systems. While ESP-NOW is better for device networks, BLE is ideal for smartphone integration and remote control applications.