Example Code for Arduino-Measuring Distance
Last revision 2025/12/31
The Sample code for driving single URM04 measuring distance function. finish driving single URM function. if use the IO expansion shield to drive the urm sensors, the measuring rate may be 20Hz or slower[if you want]. The sample code is compatible with the Arduino IDE 1.0 and also the earlier version.
Software Preparation
Arduino IDE 1.0 or earlier versions (compatible with Arduino IDE 1.0 and earlier).
Wiring Diagram
Other Preparation Work
Please place the library file Urm4parser.h into the sketch folder.
Sample Code
The library code
Note: please place the library file Urm4parser.h in to the sketch folder.
/*
# The library for the URM04 sketch
# Editor : Lauren
# Date : 2012.2.8
# Ver : 0.3
# Product: URM04 Ultrasonic sensor
# Specification
* Detecting range: 4cm-500cm
* Resolution : 1cm
* Interface : RS485
* Units: Range reported in cm
* Temperature sensor: 12 bits reading from serial port
# Description:
# finish driving single URM function
# if use the IO expansion shield to drive the urm sensors, the measuring rate may be 20Hz or slower[if you want].
# The sample code is compatible with the Arduino IDE 1.0 and also the earlier version.
*/
#if defined(ARDUINO) && ARDUINO >= 100
#include "Arduino.h"
#define printByte(args) Serial.write(args)
#else
#include "WProgram.h"
#define printByte(args) Serial.print(args,BYTE)
#endif
#define SerialPort Serial
#define urmAccount 1 // Init the account of the URM04 sensor
#define CommMAXRetry 40
#define TriggerPin 2
/******************** Variables ****************/
byte startAddr = 0x11; // Init the URM04 485 Address -- URM04 default address = 0x11
byte readingStep;
byte cmdst[10];
int urmID[urmAccount];
unsigned int urmData[urmAccount];
unsigned long managerTimer = 20;
/******************** Functions ****************/
void urmInit();
void runUrm4();
void urmTrigger(int id);
void urmReader(int id);
void transmitCommands();
void decodeURM4();
void analyzeUrmData(byte cmd[]);
/****************** Init sensor ****************/
void urmInit(){
pinMode(TriggerPin,OUTPUT); // TTL -> RS485 chip driver pin
digitalWrite(TriggerPin,LOW);// Turn the driver pin to LOW -> Turn on reading mode for the RS485 interface
// Turn the drvier pin to HIGH -> Turn on code transmitting mode for the RS485 interface
readingStep = 0;
startAddr = 0x11;
managerTimer = millis();
for(int i = 0 ;i < urmAccount; i ++){ //Init the URM04 command receiving address
urmID[i] = startAddr + i;
urmData[i] = 0;
}
SerialPort.begin(19200); // Init the RS485 interface
// Also when you are driving the URM04, you could open serial monitor to
// tracing the steps and data feedback from URM04
SerialPort.println();
SerialPort.print("The URM ID: 0x");
for(int i = 0 ;i < urmAccount; i ++){ //Init the URM04 command receiving address
SerialPort.print(urmID[i],HEX);
SerialPort.print(" ");
}
SerialPort.println(" ");
SerialPort.println("The default baudrate: 19200");
SerialPort.println("Start drive the sensors!");
for(int i = 0 ;i < 10; i++) cmdst[i] = 0; //init the URM04 protocol
cmdst[0]=0x55;
cmdst[1]=0xaa;
}
/********************* Drive URM04 and get the data code *************************/
void runUrm4(){ // You could adjust the sensor measuring rate by changing the managerTimer value
static unsigned long timer = 0;
static int num = 0; //Set the URM04 id to be drived
if(millis() - timer > managerTimer){
digitalWrite(TriggerPin, HIGH); //Turn on transmitting mode for the RS485 interface
switch(readingStep){
case 0:
urmTrigger(urmID[num]);
managerTimer = 40; //set a interval after trigger the measuring
break;
case 1:
urmReader(urmID[num]);
managerTimer = 0; //set a interval after transmitting the reading distance command
break;
case 2:
digitalWrite(TriggerPin, LOW); //Turn on reading mode for the RS485 interface
managerTimer = 10;
break;
default:
readingStep = 0; // Finish reading the distance and start a new measuring for the sensor
break;
}
if(readingStep < 2) readingStep++; //step manager
else readingStep = 0;
timer = millis();
}
}
/********************* Transmit Command via the RS485 interface ***************/
void urmTrigger(int id){ // The function is used to trigger the measuring
cmdst[2] = id;
cmdst[3] = 0x00;
cmdst[4] = 0x01;
transmitCommands();
// SerialPort.println("Trigger!");
}
void urmReader(int id){ // The function is used to read the distance
cmdst[2] = id;
cmdst[3]=0x00;
cmdst[4]=0x02;
transmitCommands();
// SerialPort.println("Ask for distance!");
}
void transmitCommands(){ // Send protocol via RS485 interface
cmdst[5]=cmdst[0]+cmdst[1]+cmdst[2]+cmdst[3]+cmdst[4];
delay(1);
for(int j = 0; j < 6; j++){
printByte(cmdst[j]);
// delayMicroseconds(10);
}
delay(2);
}
/********************* Receive the data and get the distance value from the RS485 interface ***************/
void decodeURM4(){
if(SerialPort.available()){
unsigned long timerPoint = millis();
int RetryCounter = 0;
byte cmdrd[10];
for(int i = 0 ;i < 10; i++) cmdrd[i] = 0;
int i=0;
// SerialPort.println("OK");
boolean flag = true;
boolean valid = false;
byte headerNo = 0;
while(RetryCounter < CommMAXRetry && flag)
{
if(SerialPort.available()){
cmdrd[i]= SerialPort.read();
// printByte(cmdrd[i]);
if(i > 7){
flag=false;
// printByte(0xEE);
// printByte(0xFF);
SerialPort.flush();
break;
}
if(cmdrd[i] == 0xAA){
headerNo = i;
valid = true;
}
if(valid && i == headerNo + 6){
// printByte(0xDD);
// printByte(0xFF);
flag = false;
break;
}
i ++;
RetryCounter = 0;
}
else{
RetryCounter++;
delayMicroseconds(15);
}
}
// printByte(millis() - timerPoint);
if(valid) analyzeUrmData(cmdrd);
// else SerialPort.println("Invalid feedback"); //Get an invalid error command
}
}
void analyzeUrmData(byte cmd[]){
byte sumCheck = 0;
for(int h = 0;h < 7; h ++) sumCheck += cmd[h];
if(sumCheck == cmd[7] && cmd[3] == 2 && cmd[4] == 2){
byte id = cmd[2] - startAddr;
urmData[id] = cmd[5] * 256 + cmd[6];
// SerialPort.print(id);
// SerialPort.print(":");
// SerialPort.println(urmData[id]);
}
else if(cmd[3] == 2 && cmd[4] == 2){
SerialPort.print("Sum error");
}
}
The sketch code
/*
# The Sample code for driving single URM04 measuring distance function
# Editor : Lauren
# Date : 2012.2.8
# Ver : 0.3
# Product: URM04 Ultrasonic sensor
# Specification
* Detecting range: 4cm-500cm
* Resolution : 1cm
* Interface : RS485
* Units: Range reported in cm
* Temperature sensor: 12 bits reading from serial port
# Description:
# finish driving single URM function
# if use the IO expansion shield to drive the urm sensors, the measuring rate may be 20Hz or slower[if you want].
# The sample code is compatible with the Arduino IDE 1.0 and also the earlier version.
*/
#include "Urm4parser.h"
void setup(){
urmInit(); // Init the URM04 sensor
}
void loop(){
static unsigned long timePoint = 0;
runUrm4(); // Drive URM04 Sensor and transmit the protocol to the sensor via RS485 interface
// (IO Expansion shield V5 for arduino)
decodeURM4(); // Read and get the distance value from the sensor
if(millis() - timePoint > 100){
PrintData(); // print the data
timePoint = millis();
}
// PrintData();
// delay(100);
}
void PrintData(){
Serial.print("Distance value: ");
for(int i = 0; i < urmAccount; i++){
Serial.print(urmData[i]);
Serial.print(" ");
}
/*
for(int i = 0; i < urmAccount;i ++){
Serial.print(urmID[i],HEX);
Serial.print(" ");
}
*/
Serial.println();
}
Result
The serial monitor will print the distance value measured by the URM04 sensor in the format: "Distance value: [measured distance]".
Additional Information
If using the IO expansion shield to drive the URM sensors, the measuring rate may be 20Hz or slower (if desired).
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