I tried the serial.flush() in a few ways, but none would work. Think that the delay caused by the serial.flush() is too high, because in some cases the lidar won't start working or gives more inconstant values than the orignial program.

But thanks anyway :-)

Yes, I will let you know. Honestly I don't have any clue what could fix my problem

Grabbing at straws here but you don't have much of a delay in your loop and the Serial.print may be walking on each other. take a look at https://www.baldengineer.com/when-do-you-use-the-arduinos-to-use-serial-flush.html

However, that's old DB-25 connector era thinking . . . back in the medieval days of computing!  Whatever it is, it's close.  I assume you tried different cables, etc.  I wish I had something more to suggest, but I don't.  All I can say is it's close, but some little thing is causing it to act erratically.  Like 7 data bits instead of 8, etc.  If you resolve it, could you let us know what was causing it?

Paul VE1DX

Any other ideas?

You might have better luck if you reduce the serial speed to the monitor to 9600. That is the default speed for the Uno. It looks like the UART is having trouble syncing at 115200.

putting  " lidar.begin(Serial);"   after the " Serial.begin(115200);"

Just a thought.

I am currently working on a project with a RPLidar A1 connected to an Arduino UNO, where I need to display various distances on the serial monitor. The Lidar works and the connection to the Arduino as well, because I tested the Lidar via Frame Grabber and the Lidar spins when connected to the Arduino. My problem is that the serial monitor doesn't show constant values. After a few measurements the serial monitor prints "⸮P⸮%⸮". Does anyone know how I can fix this so the serial monitor will print constantly?

Serial monitor example:

⸮P⸮%⸮ distance: 0.00 // angle: 74.50
distance: 807.50 // angle: 69.48
⸮P⸮%⸮ distance: 802.25 // angle: 70.72
⸮P⸮%⸮ distance: 0.00 // angle: 138.00
distance: 5143.75 // angle: 131.48
⸮P⸮%⸮ distance: 5060.00 // angle: 132.69
⸮P⸮%⸮ distance: 391.50 // angle: 0.41
distance: 393.00 // angle: 1.69
⸮P⸮%⸮ distance: 394.50 // angle: 2.70
⸮P⸮%⸮ distance: 0.00 // angle: 59.47
distance: 0.00 // angle: 60.67
⸮P⸮%⸮ distance: 0.00 // angle: 61.88
⸮P⸮%⸮ distance: 3370.75 // angle: 111.27

My code:

#include <RPLidar.h>

RPLidar lidar;


#define RPLIDAR_MOTOR 3

void setup() {
lidar.begin(Serial);
pinMode(RPLIDAR_MOTOR, OUTPUT);

pinMode(11,OUTPUT);
pinMode(12,OUTPUT);
pinMode(13,OUTPUT);

Serial.begin(115200);
}

void loop() {
 if(IS_OK(lidar.waitPoint())) {
  float distance = lidar.getCurrentPoint().distance;
  float angle    = lidar.getCurrentPoint().angle;
  bool startBit  = lidar.getCurrentPoint().startBit;
  byte quality   = lidar.getCurrentPoint().quality;

  if(angle < 180) {
  Serial.print("distance: ");
  Serial.print(distance);
  Serial.print(" // angle: ");
  Serial.println(angle);
  }
 }
 
  else {
    analogWrite(RPLIDAR_MOTOR, 0);

    rplidar_response_device_info_t info;
    if (IS_OK(lidar.getDeviceInfo(info, 100))) {
      lidar.startScan();

      analogWrite(RPLIDAR_MOTOR, 255);
      delay(10);
    }
  }
}