arduino 超声波测距误差较大_超声波测距的背景

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const int TrigPin = 7;
const int EchoPin = 6;
float cm;
void setup() { 

lcd. begin(16, 2);
pinMode(TrigPin, OUTPUT);
pinMode(EchoPin, INPUT) ;
}
void loop()
{ 

digitalWrite(TrigPin, LOW);
delayMicroseconds(2);
digitalWrite(TrigPin, HIGH);
delayMicroseconds(10);
digitalWrite (TrigPin, LOW);
int timer=-500;
cm=pulseIn(EchoPin, HIGH)/58.0;
cm=(int (cm*100.0))/100.0;
delay(500);
if(millis()>timer +500)
{ 

lcd. setCursor(-1,0);
lcd. print ("Distancce *CM* :");
lcd. setCursor(-1,1);
lcd. print (cm);
lcd. print ("cm ");
lcd. setCursor(-1,1);
lcd. home();
timer=millis()+500;
}
}