In addition to PIR Motion Sensor the Servo is our indispensable tool for creating an automatic door. A servo is a DC motor with a gear and feedback system, whose position can be controlled accurately. It is also called a servo motor, and often used in control systems that need angular change that can be maintained, such as robotics equipment. In the automatic door project, we can sense whether anyone is approaching through PIR Motion Sensor, send the signal to Servo to control its rotation, and finally drive the door to a fixed position. When people leave, the Servo can then close the door.
When we need to control the Servo rotation, we need to control the output to the Servo through a PWM signal. The duty cycle of the PWM directly determines the rotation position of the Servo output shaft. The figure below shows the relationship between different pulse signals and the Servo rotation angle when the frequency is 50 Hz.