Focus This Week

This week is focused on Networking and Communications. The objectives were to study network architectures and protocols (wired or wireless) and design, build, and program a network of at least two microcontrollers. I implemented an ESP-NOW wireless link connecting the Go-Kart's front steering dashboard controller (transmitting throttle percentage and alarm flags) to a rear motor-driver controller (receiving commands and modulating motor PWM).

Group Assignment — Inter-Processor Networking

The group assignment was to connect two microcontroller projects and transmit data using a shared protocol (I2C, SPI, or Serial). We mapped addressing structures and characterized transfer latency. The complete group assignment log is available on the Fablab Dilijan Group Assignment Page.

Comparison of Bus Networks

Individual Assignment — Dashboard-to-Motor Link

Running long physical control wires from the front steering wheel to the rear motor of the Go-Kart can introduce electrical noise and mechanical failure. To resolve this, I implemented ESP-NOW, an Espressif wireless protocol that sends packets directly between ESP32 MAC addresses without requiring a Wi-Fi router.

Network Packet Frame Layout

I defined a structured data payload frame in C++ to package speed and alarm commands:

// Shared Packet Struct definition
struct __attribute__((packed)) TelemetryPacket {
    uint8_t throttle; // 0 - 100%
    uint8_t alarmFlag; // 0: Normal, 1: High Temperature, 2: Battery low
    uint32_t timestamp; // millis() tick counts for latency check
};

Firmware Code — Sender (Dashboard Board)

This script reads the throttle sensor and transmits the data frame to the MAC address of the receiver board.

// ESP-NOW Sender Program
#include <esp_now.h>
#include <WiFi.h>

// MAC Address of the Receiver (Rear Motor Controller)
uint8_t receiverAddress[] = {0xFC, 0xF5, 0xC4, 0x83, 0x1A, 0x4C};

struct __attribute__((packed)) TelemetryPacket {
    uint8_t throttle;
    uint8_t alarmFlag;
    uint32_t timestamp;
} myData;

void onDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("Send status: ");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  
  if (esp_now_init() != ESP_OK) {
    Serial.println("Error initializing ESP-NOW");
    return;
  }
  
  esp_now_register_send_cb(onDataSent);
  
  // Register peer
  esp_now_peer_info_t peerInfo;
  memcpy(peerInfo.peer_addr, receiverAddress, 6);
  peerInfo.channel = 0;  
  peerInfo.encrypt = false;
  
  if (esp_now_add_peer(&peerInfo) != ESP_OK){
    Serial.println("Failed to add peer");
    return;
  }
}

void loop() {
  myData.throttle = map(analogRead(2), 620, 3470, 0, 100);
  myData.alarmFlag = (myData.throttle > 80) ? 1 : 0;
  myData.timestamp = millis();
  
  esp_now_send(receiverAddress, (uint8_t *) &myData, sizeof(myData));
  delay(100);
}

Firmware Code — Receiver (Motor Board)

This script receives the package, unpacks the data frame, checks the latency difference, and outputs control commands.

// ESP-NOW Receiver Program
#include <esp_now.h>
#include <WiFi.h>

struct __attribute__((packed)) TelemetryPacket {
    uint8_t throttle;
    uint8_t alarmFlag;
    uint32_t timestamp;
} incomingData;

void onDataRecv(const uint8_t * mac, const uint8_t *incomingBytes, int len) {
  memcpy(&incomingData, incomingBytes, sizeof(incomingData));
  
  uint32_t latency = millis() - incomingData.timestamp;
  
  Serial.print("Recv Speed: ");
  Serial.print(incomingData.throttle);
  Serial.print("%, Alarm: ");
  Serial.print(incomingData.alarmFlag);
  Serial.print(", Latency: ");
  Serial.print(latency);
  Serial.println(" ms");
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  
  if (esp_now_init() != ESP_OK) {
    Serial.println("Error initializing ESP-NOW");
    return;
  }
  
  esp_now_register_recv_cb(onDataRecv);
}

void loop() {
  // Free running receiver loop
}

Original Code Files

Download the sender and receiver program source files:

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Week 11 — Summary

This week focused on network architectures and wireless protocols. Here is a summary of the accomplishments: