Arduino TFMini Lidar sensors and speaker

Question

I have this code for the TFMini Lidar sensors and Speaker. I Need help figuring why I'm using this calculation in my code and why if I removed it the lidar will not give me any measurement? (see below plz).

And my code now it's only one sensor is working pins (4,5) I don't know why the three of them don't work together. Thanks in advance.

I took this code from the internet My coding experience is basic .

rx[i] = TFMiniOne.read();
if (rx[0] != 0x59) {
  i = 0;
} else if (i == 1 && rx[1] != 0x59) {
  i = 0;
} else if (i == 8) {
  for (j = 0; j < 8; j++) {
    checksum += rx[j];
  }
  if (rx[8] == (checksum % 256)) {
    *distance = rx[2] + rx[3] * 256;
    *strength = rx[4] + rx[5] * 256;
  }
  i = 0;
} else {
  i++;
} 

Here is the complete code:

#include "Talkie.h"
#include "Vocab_US_Large.h"
#include <SoftwareSerial.h>
#include "TFMini.h"
TFMini tfminiOne;
TFMini tfminiTwo;
TFMini tfminiThree;

Talkie voice;
const int Speaker = 3;

//Declaring variables and constants

SoftwareSerial TFMiniOne (4,5);    //(RX, TX)
SoftwareSerial TFMiniTwo (6,7);
SoftwareSerial TFMiniThree (8,9);

void getTFminiData(int* distance, int* strength) {
  static char i = 0;
  char j = 0;
  int checksum = 0; 
  static int rx[9];
  if (TFMiniOne.available()) {  
    // Serial.println( "tfmini serial available" );
    rx[i] = TFMiniOne.read();
    if (rx[0] != 0x59) {
      i = 0;
    } else if (i == 1 && rx[1] != 0x59) {
      i = 0;
    } else if (i == 8) {
      for (j = 0; j < 8; j++) {
        checksum += rx[j];
      }
      if (rx[8] == (checksum % 256)) {
        *distance = rx[2] + rx[3] * 256;
        *strength = rx[4] + rx[5] * 256;
      }
      i = 0;
    } else {
      i++;
    } 
  }  
}


void setup() {
  pinMode(Speaker, OUTPUT);
 
  //Initializing 
  Serial.begin (115200);
  while(!Serial);                     //Wait for USB Serial Port to connect
  Serial.println("Initializing...");
  TFMiniOne.begin (TFMINI_BAUDRATE);       

  //Initializing TFMini Sensors
  tfminiOne.begin(&TFMiniOne);
  tfminiTwo.begin(&TFMiniTwo);    
}

void loop() { 
  int distance = 0;
  int strength = 0;

  getTFminiData(&distance, &strength);
  while (!distance) {
    getTFminiData(&distance, &strength);
    if (distance) {
      Serial.print(distance);
      Serial.print("cm\t");
      Serial.print("strength: ");
      Serial.println(strength);
    }
  }

  delay(100);

  if (distance > 30) {
    digitalWrite(Speaker,HIGH);
    voice.say(sp2_ALERT);
    voice.say(sp2_F);
  } else {
    digitalWrite(Speaker,LOW);
  }

  if (distance > 20) {
    digitalWrite(Speaker,HIGH);
    voice.say(sp2_ALERT);
    voice.say(sp2_L);
  } else {
    digitalWrite(Speaker,LOW);
  }

  if (distance < 15) {
    digitalWrite(Speaker,HIGH);
    voice.say(sp2_ALERT);
    voice.say(sp2_R);
  } else {
    digitalWrite(Speaker,LOW);
  }
  delay(300);

Answer 1

I don't know why the three of them don't work together.

I already answered that question in my answer to your previous question.

why I'm using this calculation in my code and why if I removed it the lidar will not give me any measurement?

That code part is reading the data from the first SoftwareSerial interface. If you don't read this data (by removing this code part) you are not reading any data from the TFMini, thus you don't have any measurement. If you want measurements from the lidar sensor, don't remove the code part, that actually reads the measurements.

Besides that I will explain the complete function here in comments to the code. Before that, you should understand what the static keyword means here. Normal variables, that get declared inside a function, (aka local variables) will get destroyed, when the code reaches the end of the function. Variables marked with the keyword static will continue to exist and hold their value also after the function ended. They act a lot like global variables, though their namespace is local to the function (thus you can declare other variables with that name in other parts of your code).

void getTFminiData(int* distance, int* strength) {
  static char i = 0; // this counter variable denotes the position of the next to be received byte in the buffer rx.
  char j = 0; // temporary counter variable
  int checksum = 0; // will be used to calculate the checksum, so that it can be compared to the one send with the data
  static int rx[9]; // this is the receive buffer, where the received data will be put

  if (TFMiniOne.available()) { // When data is available on the serial interface, read one byte  
    // Serial.println( "tfmini serial available" );
    // read one byte into the current position in the buffer
    rx[i] = TFMiniOne.read();

    // A valid message starts with two bytes of the value 0x59, so we restart, if the current message doesn't have that. (checking the first two bytes with these two if statements)
    if (rx[0] != 0x59) {
      i = 0;
    } else if (i == 1 && rx[1] != 0x59) {
      i = 0;
    } else if (i == 8) { // if we received 9 bytes (positions 0 to 8 in the buffer), the message is complete --> process it

      // Calculating the checksum by adding all bytes together
      for (j = 0; j < 8; j++) {
        checksum += rx[j];
      }

      // Comparing the calculated checksum with the last byte, that was received, (which is the checksum)
      // as the checksum is only one byte, we calculate the modulo with 256, thus only leaving the number range 0-255.
      if (rx[8] == (checksum % 256)) {
        // The checksums are equal, so the data is valid and we can proceed
        // The values for distance and strength have two bytes. Thus we need to put these bytes together into one value.
        *distance = rx[2] + rx[3] * 256;
        *strength = rx[4] + rx[5] * 256;
      }

      // reset the counter, since we have a full message and can now receive the next message
      i = 0;
    } else {
      // increment the counter variable to the next position, if we are currently receiving the bytes of a valid message
      i++;
    } 
  }  
}

I hope this makes the code clearer. As already said the my previous answer, it doesn't make much sense, to first use the TFMini library (declaring the corresponding objects) and then doing the communication yourself. I would suggest, that you look closer into the TFMini library. Try the examples, that surely come with the library. Use the libraries functions to communicate with the sensors. That will make it way easier for you, since the library will do the communications for you.

Answer 2

I can't answer the first part of your question as I don't understand what you're asking. However:

I don't know why the three of them don't work together.

That doesn't work for 2 reasons:

1. Your receiving routine specifically references only one TFMini serial port, and
2. It is impossible to receive from more than one SoftwareSerial port at a time.

If you want to use multiple units you really should choose a microcontroller that has enough hardware UARTs to do the job. The Uno is not a suitable board.

Try the Mega2560 or one of the myriad of 32-bit ARM or MIPS boards.