5.4.9 Project 5.1 Control the Door

1. Description

Automatic doors and windows need power device, which will become more automatic with a 180 degree servo and some sensors. Adding a raindrop sensor, you can achieve the effect of closing windows automatically when raining. If adding a RFID, we can realize the effect of swiping to open the door and so on.

2. Component Knowledge

Servo: Servo is a position servo driver device consists of a housing, a circuit board, a coreless motor, a gear and a position detector.

Its working principle is that the servo receives the signal sent by MCU or receiver and produces a reference signal with a period of 20ms and width of 1.5ms, then compares the acquired DC bias voltage to the voltage of the potentiometer and obtain the voltage difference output.

The IC on the circuit board judges the direction of rotation, and then drives the coreless motor to start rotation. The power is transmitted to the swing arm through the reduction gear, and the signal is sent back by the position detector to judge whether the positioning has been reached, which is suitable for those control systems that require constant angle change and can be maintained.

When the motor speed is constant, the potentiometer is driven to rotate through the cascade reduction gear, which leads that the voltage difference is 0, and the motor stops rotating. Generally, the angle range of servo rotation is 0° –180 °.

The pulse period of the control servo is 20ms, the pulse width is 0.5ms

2.5ms, and the corresponding position is -90°~ +90°. Here is an example of a 180° servo:

In general, servo has three lines in brown, red and orange. The brown wire is grounded, the red one is a positive pole line and the orange one is a signal line.

3. Pin

The servo of the window	5
The servo of the door	13

4. Test Code

#include <ESP32Servo.h>
Servo myservo;  // create servo object to control a servo
                // 16 servo objects can be created on the ESP32

int pos = 0;    // variable to store the servo position
// Recommended PWM GPIO pins on the ESP32 include 2,4,12-19,21-23,25-27,32-33
int servoPin = 13;

void setup() {
    // Allow allocation of all timers
    ESP32PWM::allocateTimer(0);
    ESP32PWM::allocateTimer(1);
    ESP32PWM::allocateTimer(2);
    ESP32PWM::allocateTimer(3);
    myservo.setPeriodHertz(50);    // standard 50 hz servo
    myservo.attach(servoPin, 1000, 2000); // attaches the servo on pin 18 to the servo object
    // using default min/max of 1000us and 2000us
    // different servos may require different min/max settings
    // for an accurate 0 to 180 sweep

}

void loop() {
    for (pos = 0; pos <= 180; pos += 1) { // goes from 0 degrees to 180 degrees
        // in steps of 1 degree
        myservo.write(pos);    // tell servo to go to position in variable 'pos'
        delay(15);             // waits 15ms for the servo to reach the position
    }
    for (pos = 180; pos >= 0; pos -= 1) { // goes from 180 degrees to 0 degrees
        myservo.write(pos);    // tell servo to go to position in variable 'pos'
        delay(15);             // waits 15ms for the servo to reach the position
    }

}

5. Test Result

The servo of the door turns with the door, back and forth