11. Embedded Networking and Communications

Here you can see what we did in our group assignment. Group Assignment

This week I wanted to create a bidirectional UART communication system between two Seeed Studio Xiao RP2040. One acts as a master, reading a potentiometer value, and the other as a slave, controlling a NEMA stepper motor using an A4988 driver. The slave can also send a command back to the master when a button is pressed.

My first idea was to comunicate via BLE between 2 Xiao C3 but unfortunetly one Xiao C3 burned during testing. So I had to use the Xiao RP2040 due to the lack of time. Overall I had never used UART to comunicate 2 Xiaos so still was a new experience for me.

System Overview

  • Master: Reads a potentiometer and sends values to the slave via UART. Listens for button press messages from the slave.
  • Slave: Receives speed values and controls the stepper motor. When a button is pressed, it notifies the master.

I had to use a protoboard because im doing the testing with the PCB I made for the CNC (Next week assignment) And I want to avoid any malfunction on the pcb as well as doing test on it

How to connect

  • TX (Master) → RX (Slave)
  • RX (Master) ← TX (Slave)
  • GND ↔ GND (Must have common ground)
  • Potentiometer → Master D0
  • Button → Slave D7
  • A4988 DIR (D2), STEP (D3)

Master Code 


void setup() {
Serial1.begin(9600); // UART communication
}

void loop() {
int potValue = analogRead(A0);
int speedValue = map(potValue, 0, 1023, 500, 2000);

Serial1.println(speedValue);

if (Serial1.available()) {
  String message = Serial1.readStringUntil('\n');
  if (message == "BUTTON_PRESSED") {
	Serial.println("Button was pressed on the slave!");
  }
}

delay(100);
}

Slave Code (Xiao RP2040)


#define DIR_PIN 2
#define STEP_PIN 3
#define BUTTON_PIN 7

bool motorDirection = true;
int speedValue = 1000;

void setup() {
Serial1.begin(9600);
pinMode(DIR_PIN, OUTPUT);
pinMode(STEP_PIN, OUTPUT);
pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
if (Serial1.available()) {
  speedValue = Serial1.parseInt();
}

static bool lastButtonState = HIGH;
bool currentButtonState = digitalRead(BUTTON_PIN);
if (lastButtonState == HIGH && currentButtonState == LOW) {
  Serial1.println("BUTTON_PRESSED");
  motorDirection = !motorDirection;
  digitalWrite(DIR_PIN, motorDirection);
}
lastButtonState = currentButtonState;

digitalWrite(STEP_PIN, HIGH);
delayMicroseconds(100);
digitalWrite(STEP_PIN, LOW);
delayMicroseconds(speedValue);
}
  • Both devices comunicate at 9600 baud for UART.
  • The button uses the internal pull-up and must be wired to GND.
  • The A4988 driver must be powered at 12V and have common ground with the Xiao.

I had an issue with the code in which it wont allow me to recieve the information from the potenciometer I had an error in the code so I asked chatGPT to help me solve the issue.

Useful links