Networking and Communications

#include <Arduino.h>
#include <WiFi.h>
#include <esp_now.h>

#define Flex_Sensor 2

uint8_t Receiver_Address[] = {0x58, 0xE6, 0xC5, 0x10, 0x43, 0xCC};

typedef struct Struct_Message {
  int Angle;
} Struct_Message;

Struct_Message Out_Going_Data;

float Filter_Value = 0;
float Smooth_Factor = 0.3;

void On_Data_Sent(const wifi_tx_info_t* info, 
esp_now_send_status_t status) {
}

void setup() {
  Serial.begin(115200);
  
  WiFi.mode(WIFI_STA);
  if (esp_now_init() != ESP_OK) {
    Serial.println("Error at startup ESP-NOW");
    return;
  }
  
  esp_now_register_send_cb(On_Data_Sent);
  
  esp_now_peer_info_t peerInfo = {};
  memcpy(peerInfo.peer_addr, Receiver_Address, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;
  
  if (esp_now_add_peer(&peerInfo) != ESP_OK) {
    Serial.println("Error adding the receiver");
    return;
  }
}

void loop() {
  int Flex_Value = analogRead(Flex_Sensor); 
  Filter_Value = Filter_Value * (1 - Smooth_Factor) + Flex_Value * 
  Smooth_Factor; 

  float Normalized_Value = Filter_Value / 3370.0; 
  Normalized_Value = constrain(Normalized_Value, 0, 1); 
  float Normalized_Value_Corrected = pow(Normalized_Value, 10.0); 
  
  int Servo_Angle = Normalized_Value_Corrected * 270; 

  Serial.print("Flex: "); 
  Serial.print(Flex_Value);
  Serial.print(" | Angle Sent: "); 
  Serial.println(Servo_Angle);

  Out_Going_Data.Angle = Servo_Angle;
  esp_now_send(Receiver_Address, (uint8_t *) &Out_Going_Data, 
  sizeof(Out_Going_Data));

  delay(50); 
}
                                

Explanation

ESP-NOW is a fast, connectionless wireless communication protocol developed by Espressif. In this architecture, the sender node is configured to capture a physical analog input, process it into a target mechanical angle, and wirelessly broadcast this payload directly to a paired receiver device's MAC address without routing through a standard Wi-Fi network.

Libraries and Definitions

• #include <esp_now.h> and <WiFi.h>: Essential libraries that expose the underlying Wi-Fi radio peripheral of the ESP32. They are necessary to bypass standard network protocols and establish a direct MAC-to-MAC communication layer.
• uint8_t Receiver_Address[]: It permanently stores the unique MAC or Media Access Control address of the destination receiving node. This hexadecimal array acts as the final routing destination for all outgoing data packets.
• typedef struct Struct_Message: Define a strictly typed data payload. By encapsulating the target integer angle within a structured format, the compiler ensures identical memory alignment and size allocation between the transmitting and receiving devices, preventing data corruption during byte-level transfer.

Hardware Setup and Configuration

• WiFi.mode(WIFI_STA): It forces the internal Wi-Fi radio to operate exclusively in Station mode. This is a prerequisite for the ESP-NOW protocol, as it activates the wireless hardware without actively searching for or connecting to a local internet router.
• esp_now_init(): Initializes the low-level communication protocols within the ESP32 network, verifying radio availability and allocating the necessary memory buffers for packet transmission.
• esp_now_add_peer(&peerInfo): Register the specific receiving microcontroller as a valid communication endpoint. Link the destination MAC address to the transmitter's internal peer array, thus establishing the connectionless broadcast tunnel.

Data Transmission

• Signal Obtainment: The raw analog reading, mathematical normalization, and exponential curve correction used to convert the physical resistance of the flex sensor into a usable angle of 0 to 270 degrees are identical to those in my previous work with sensors. For a detailed analysis of this specific filtering and mapping logic, see the documentation for week 9.

Inputs Devices


• Packet Injection: esp_now_send() takes the final computed Servo_Angle, serializes the data structure into a raw byte array, and directly injects it into the 2.4GHz RF spectrum, targeting exclusively the registered receiver MAC address.
• Transmission Pacing: delay(50) introduces a brief, mandatory 50-millisecond blocking pause at the end of the execution cycle. This crucial governor prevents the main loop from flooding the wireless spectrum and exhausting the microcontroller's internal transmission buffers.