Hi I am new and not so familiar with this area. I have made a construction but I don't know which battery to use for it. Is a 9V block battery OK or does it have too little power? If it has too little power, which one should I use? My goal is that when the ultrasonic sensor (HC-SR04) detects an object within 40 cm, the motors should be activated for 5 seconds. In the code there is only one motor but I plan to use 2. I am using a HC-SR04 Ultrasonic sensor, Arduino Uno, 9V battery, L298n motor driver and 2 Hobby dc motors. Many thanks in advance 
Code:
// defines pins numbers
const int trigPin = 9;
const int echoPin = 10;
const int buzzer = 13;
// Project by - Be innovative with Prasad
// title - ultrasonic sensor project with buzzer and Arduino
// defines variables
long duration;
int distance;
int safetyDistance;
void setup()
{
pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
pinMode(echoPin, INPUT); // Sets the echoPin as an Input
pinMode(buzzer, OUTPUT);
Serial.begin(9600); // Starts the serial communication
}
void loop()
{
// Clears the trigPin
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
// Sets the trigPin on HIGH state for 10 micro seconds
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
// Reads the echoPin, returns the sound wave travel time in microseconds
duration = pulseIn(echoPin, HIGH);
// Calculating the distance
distance= duration*0.034/2;
safetyDistance = distance;
if (safetyDistance <= 20) // You can change safe distance from here changing value Ex. 20 , 40 , 60 , 80 , 100, all in cm
{
digitalWrite(buzzer, HIGH);
}
else{
digitalWrite(buzzer, LOW);
}
}
