UART Serial Communication Between UNO and Leonardo for Controlling Servo With Potentiometer

[chillghosst]

Hi, I am watching a tutorial but he uses UNO and Mega and I use a UNO and Leonardo. I am trying to control a servo -which is connected to the leonardo- with a 10k potentiometer -which is connected to the UNO- and I can't control it. I read topics in here about serial connection and I learned about there is Serial in UNO and Serial1 on leonardo.

My wiring diagram:

This is my code for UNO:

int potpin = A0;
int val;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  

}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.print("Sent: ");
  Serial.println(val);
  val = analogRead(potpin);
  val = map(val, 0, 1023, 0, 180);
  Serial.write(val);
  delay(15);
}

And this is for leonardo:

#include <Servo.h>
Servo myservo;
int val;

void setup() {
  myservo.attach(9);
  Serial.begin(9600);
  Serial1.begin(9600);
  Serial.println("Leo is ready!");
}

void loop() {
  if(Serial1.available() > 0){
    val = Serial1.read();
    myservo.write(val);
    Serial.print("Received:");
    Serial.print(val);
  }
  delay(15);
}

I tried different codes for leonardo and this is the last version. When I run this codes the servo shakes like crazy and sometimes moves to a different position. What am I doing wrong?

[PaulRB]

You can't use Serial, pins 0, 1 for this on Uno because on Uno they are used for code upload and serial monitor. If you want to connect something to Uno using UART, you need to use Software Serial and 2 other pins.

On Leonardo, it's ok to use pins 0, 1 because they are not used for code upload & serial monitor. Those pins are associated with Serial1 on Leonardo, as you have read.

[van_der_decken]

Every 15 ms you transmit a new value.

But when you receive it, you also print out up to 12 characters at 9600 baud. How long does that take? And then on top of that you wait 15 ms. Is it any wonder that the transmitter is overrunning the receiver and creating chaos?

Try backing off on how often you transmit a new value to start with, and not printing the received value or delaying in the receiver and see how it goes from there.

Oh, and don't power the servo from the Leonardo. It takes way more current than you should be asking for from the board.

[horace]

you are using pins 0 and 1 on the UNO for UNO/Leonardo communication which are also used for Serial monitor IO

on UNO use AltSoftSerial

on the leonardo Serial uses a native USB (uart0)
Serial1 is hardware serial port pin 1 is Tx and pin 0 is Rx (5V logic)

[chillghosst]

I tried powering from a 6 V battery but didn't worked. Perhaps i didn't correctly wire the common ground but I don't know.

[chillghosst]

Update:
I asked a chatgpt one more time and this time it worked! Here is the last codes for Uno and Leonardo respetctively:

int potpin = A0;
int val;

void setup() {
  Serial.begin(9600); // Debug via USB
}

void loop() {
  val = analogRead(potpin);
  val = map(val, 0, 1023, 0, 180);
  Serial.println(val);  // Send as ASCII text with newline
  delay(15);
}

#include <Servo.h>

Servo myservo;
int val;
int lastVal = -1; // To help filter out minor changes

void setup() {
  myservo.attach(9);
  Serial.begin(9600);   // USB Serial for debugging
  Serial1.begin(9600);  // UART for communication with Uno
  Serial.println("Leonardo Ready");
}

void loop() {
  // Check if a complete number is available on Serial1
  if (Serial1.available() > 0) {
    val = Serial1.parseInt();  // Read the integer sent from Uno
    // Validate range and update only if the change is significant
    if (val >= 0 && val <= 180 && abs(val - lastVal) > 2) {
      myservo.write(val);
      lastVal = val;
      Serial.print("Received: ");
      Serial.println(val);
    }
  }
  delay(15);
}

Sadly my pc gave bluescreen and I lose my conversation with chatgpt but I copied the code before that fortunately.

[chillghosst]

Anybody can explain why it worked?

[van_der_decken]

Ask ChatGPT. I wouldn't have offered to help if I'd known the code came from there.

[chillghosst]

I wrote the code from tutorial but it didn't worked so I ask to gpt. Why did you speak like that bro what did I say wrong.

[Brazilino]

@chillghosst

Why did you speak like that bro what did I say wrong.

Just not to let you wondering: most people here at the forum are not chatGPT fans because we frequently see people looking for easy and quick solutions on the AI instead of learning and then bringing broken code here for the human intelligence to fix it.

If you want to understand it better, take a look at the topic https://forum.arduino.cc/t/officially-ban-chatgpt-and-ai/

Generally, there is no effort on the OP part and that bothers the helpers.

I don't think that is your case. Your project seems to be exactly for learning purposes (otherwise you would be using only one of the boards to read the pot and control the servo). So, to answer your question

@chillghosst

Anybody can explain why it worked?

I suggest you to take a look in what this line does:

@chillghosst

val = Serial1.parseInt();

and how Serial comms work. A good place to take a look is on the famous Robin2 Serial Input Basics .

And believe on this tip:

@van_der_decken

Oh, and don't power the servo from the Leonardo. It takes way more current than you should be asking for from the board.

[chillghosst]

Thanks!