Wemos Mini and HC-SR04 ultrasonic sensor

The HC-SR04 ultrasonic sensor uses sonar to determine distance to an object like bats or dolphins do. Ultrasonic ranging module HC-SR04 provides 2cm – 400cm measurement, the ranging accuracy can reach to 3mm. The modules includes ultrasonic transmitters, receiver and control circuit.

How it works:
(1) IO trigger for at least 10us high level signal
(2) The Module automatically sends eight 40 kHz and detects whether there is a pulse signal back.
(3) If there is a signal back, through high level , time of high output IO duration is the time from sending ultrasonic pulse to return.

Test distance = (high level time × velocity of sound (340M/S) / 2)

Here is  a picture of one of these modules

Parts List

Here are the parts I used

Wiring

The HC-SR04 Ultrasonic Module has 4 pins these are Ground, VCC, Trig and Echo. The Ground and the VCC pins of the module needs to be connected to the Ground and the 5 volts pins on the Wemos Mini respectively and the trig and echo pins to any Digital I/O pin on the Wemos Mini, in our example we use D6 for Trig and D7 for Echo

Here is a breadboard layout showing how to connect a wemos mini and HC-SR04

Code

#define echoPin D7 // Echo Pin
#define trigPin D6 // Trigger Pin

long duration, distance; // Duration used to calculate distance

void setup()
{
Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}

void loop()
{
/* The following trigPin/echoPin cycle is used to determine the
distance of the nearest object by bouncing soundwaves off of it. */
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
//Calculate the distance (in cm) based on the speed of sound.
distance = duration/58.2;
Serial.println(distance);
//Delay 50ms before next reading.
delay(50);
}

Output

As you can see in the output below no object was detected inside about 73 centimetres on average