怎么制作arduino雷达避让小车，材料有arduino uno板，超声波传感器，L293D，两个电机，舵机，锂电池，车轮，7805。并帮我写arduino代码。要求能跟前面障碍物保持20cm距离，障碍物前进小车前进，障碍物后退小车后退

制作arduino雷达避让小车需要按照以下步骤进行：

1. 搭建电路：将超声波传感器、L293D、两个电机、舵机、锂电池、车轮、7805等电子元件按照电路图连接起来。

2. 编写arduino代码：将以下代码上传到arduino uno板上，实现小车的自动避障功能。

#include <Servo.h>

#define trigPin 2
#define echoPin 3
#define motorPin1 4
#define motorPin2 5
#define motorPin3 6
#define motorPin4 7

int motorSpeed = 200;

Servo myservo;
int pos = 90;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(motorPin1, OUTPUT);
  pinMode(motorPin2, OUTPUT);
  pinMode(motorPin3, OUTPUT);
  pinMode(motorPin4, OUTPUT);
  myservo.attach(9);
  Serial.begin(9600);
}

void loop() {
  int distance = getDistance();
  Serial.print("Distance: ");
  Serial.println(distance);
  
  if (distance > 20) {
    goForward();
  } else {
    stop();
    delay(500);
    backOff();
    delay(1000);
    turnLeft();
    delay(1000);
    goForward();
  }
}

int getDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  int duration = pulseIn(echoPin, HIGH);
  int distance = duration * 0.034 / 2;
  
  return distance;
}

void goForward() {
  digitalWrite(motorPin1, HIGH);
  digitalWrite(motorPin2, LOW);
  digitalWrite(motorPin3, HIGH);
  digitalWrite(motorPin4, LOW);
}

void stop() {
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, LOW);
  digitalWrite(motorPin3, LOW);
  digitalWrite(motorPin4, LOW);
}

void backOff() {
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, HIGH);
  digitalWrite(motorPin3, LOW);
  digitalWrite(motorPin4, HIGH);
}

void turnLeft() {
  myservo.write(pos+45); 
}

void turnRight() {
  myservo.write(pos-45); 
}