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1.3.2 Servo
Introduction
In this project, we will learn how to make the servo rotate.
Required Components
In this project, we need the following components.
It’s definitely convenient to buy a whole kit, here’s the link:
Name |
ITEMS IN THIS KIT |
LINK |
---|---|---|
Raphael Kit |
337 |
You can also buy them separately from the links below.
COMPONENT INTRODUCTION |
PURCHASE LINK |
---|---|
Schematic Diagram
Experimental Procedures
Step 1: Build the circuit.
Step 2: Go to the folder of the code.
cd ~/raphael-kit/python/
Step 3: Run the executable file.
sudo python3 1.3.2_Servo.py
After the program is executed, the servo will rotate from 0 degrees to 180 degrees, and then from 180 degrees to 0 degrees, circularly.
Code
Note
You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like raphael-kit/python
. After modifying the code, you can run it directly to see the effect.
import RPi.GPIO as GPIO
import time
SERVO_MIN_PULSE = 500
SERVO_MAX_PULSE = 2500
ServoPin = 18
def map(value, inMin, inMax, outMin, outMax):
return (outMax - outMin) * (value - inMin) / (inMax - inMin) + outMin
def setup():
global p
GPIO.setmode(GPIO.BCM) # Numbers GPIOs by BCM
GPIO.setup(ServoPin, GPIO.OUT) # Set ServoPin's mode is output
GPIO.output(ServoPin, GPIO.LOW) # Set ServoPin to low
p = GPIO.PWM(ServoPin, 50) # set Frequecy to 50Hz
p.start(0) # Duty Cycle = 0
def setAngle(angle): # make the servo rotate to specific angle (0-180 degrees)
angle = max(0, min(180, angle))
pulse_width = map(angle, 0, 180, SERVO_MIN_PULSE, SERVO_MAX_PULSE)
pwm = map(pulse_width, 0, 20000, 0, 100)
p.ChangeDutyCycle(pwm)#map the angle to duty cycle and output it
def loop():
while True:
for i in range(0, 181, 5): #make servo rotate from 0 to 180 deg
setAngle(i) # Write to servo
time.sleep(0.002)
time.sleep(1)
for i in range(180, -1, -5): #make servo rotate from 180 to 0 deg
setAngle(i)
time.sleep(0.001)
time.sleep(1)
def destroy():
p.stop()
GPIO.cleanup()
if __name__ == '__main__': #Program start from here
setup()
try:
loop()
except KeyboardInterrupt: # When 'Ctrl+C' is pressed, the program destroy() will be executed.
destroy()
Code Explanation
p = GPIO.PWM(ServoPin, 50) # set Frequecy to 50Hz
p.start(0) # Duty Cycle = 0
Set the servoPin to PWM pin, then the frequency to 50hz, and the period to 20ms.
p.start(0): Run the PWM function,and set the initial value to 0.
def setAngle(angle): # make the servo rotate to specific angle (0-180 degrees)
angle = max(0, min(180, angle))
pulse_width = map(angle, 0, 180, SERVO_MIN_PULSE, SERVO_MAX_PULSE)
pwm = map(pulse_width, 0, 20000, 0, 100)
p.ChangeDutyCycle(pwm)#map the angle to duty cycle and output it
Create a function, setAngle() to write angle that ranges from 0 to 180 into the servo.
angle = max(0, min(180, angle))
This code is used to limit the angle within the range 0-180°.
The min() function returns the minimum of the input values. If 180<angle, then return 180,if not, return angle.
The max() method returns the maximum element in an iterable or largest of two or more parameters. If 0>angle, then return 0, if not, return angle.
pulse_width = map(angle, 0, 180, SERVO_MIN_PULSE, SERVO_MAX_PULSE)
pwm = map(pulse_width, 0, 20000, 0, 100)
p.ChangeDutyCycle(pwm)
To render a range 0 ~ 180 ° to the servo, the pulse width of the servo is set to 0.5ms(500us)-2.5ms(2500us).
The period of PWM is 20ms(20000us), thus the duty cycle of PWM is (500/20000)%-(2500/20000)%, and the range 0 ~ 180 is mapped to 2.5 ~ 12.5.