BakeBit - Servo

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1 Introduction

Servo

• The BakeBit - Servo is a servo module which contains a DC motor and a transmission system.
• Its input signal is PWM. The motor's steering angle changes according to PWM signals' changes. The input PWM's frequency is 50Hz and its width is 0.5ms—2.5ms. The motor's steering angle is 0 - 180°。
• A PWM input steers the motor to an angle. When no input signals are applied the motor will stop.

2 Hardware Spec

• Standard 2.0mm pitch 4-Pin BakeBit Interface

Servo's dimension

• Spec:

• Pin Description:

Pin	Name	Description
1	SIG	Signal
2	NC	Not Connected
3	5V	5V Supply Voltage
4	GND	Ground

3 Code Sample: Servo and Rotary Angle Sensor

By running this code sample users can control a servo with the BakeBit - Rotary Angle Sensor module. The servo's streering angle is between 0～180 degrees.

3.1 Hardware Connection

Connect the servo module to the NEO-Hub at D5 and the rotary angle sensor module to the NEO-Hub at A0:

3.2 Source Code

import time
import bakebit
import random
 
# Connect the servo to digital port D5
# SIG,NC,VCC,GND
servo = 5
 
# Connect the BakeBit Rotary Angle Sensor to analog port A0
# SIG,NC,VCC,GND
potentiometer = 0
 
# Reference voltage of ADC is 5v
adc_ref = 5
 
# Vcc of the bakebit interface is normally 5v
bakebit_vcc = 5
 
# Full value of the rotary angle is 180 degrees, as per it's specs (0 to 180)
full_angle = 180
old_degrees = -1
 
bakebit.pinMode(potentiometer,"INPUT")
bakebit.bakeBitServo_Attach(servo)
 
 
while True:
    try:
        # Read sensor value from potentiometer
        sensor_value = bakebit.analogRead(potentiometer)
 
        # Calculate voltage
        voltage = round((float)(sensor_value) * adc_ref / 1023, 2)
 
        # Calculate rotation in degrees (0 to 180)
        degrees = int((voltage * full_angle) / bakebit_vcc)
 
        if degrees != old_degrees:
            print("sensor_value = %d voltage = %.2f degrees = %d" % (sensor_value, voltage, degrees))
            bakebit.bakeBitServo_Write(servo, degrees)
 
        old_degrees = degrees
 
    except KeyboardInterrupt:
        bakebit.bakeBitServo_Detach(servo)
        break
    except IOError:
        print ("Error")

Github

3.3 Run Code Sample

Before you run the code sample you need to follow the steps in bakebit tutorial to intall the BakeBit package.
Enter the "BakeBit/Software/Python" directory and run the "bakebit_prj_Servo_And_RotaryAngleSensor.py" program:

cd ~/BakeBit/Software/Python
sudo python bakebit_prj_Servo_And_RotaryAngleSensor.py

3.4 Observation

When you rotate the rotary angle module the servo will be steered between 0 to 180 degrees.

4 Resources

• [Specification](BakeBit - Servo Specification.pdf)
• [BakeBit Github Project Page](https://github.com/friendlyarm/BakeBit)
• [BakeBit Starter Kit User's Manual](http://wiki.friendlyarm.com/bakebit/bakebit_starter_kit_manual_en.pdf)

5 Update Log

5.1 December-14-2016

• Released English Version