arduino tutorial 2: secret door knock detector. agenda 1.sensor review 2.make: calibrate sensor...
TRANSCRIPT
Arduino Tutorial 2:Secret Door Knock Detector
Agenda
1.Sensor Review2.MAKE: calibrate sensor3.PWM4.Motors 5.MAKE: calibrate motor6.Validation algorithm7.MAKE: Secret Knock Detector8.Links
Analog Review• Analog Arduino mapping: 0-5V 0 -1023 analogRead(pin)
• Piezo: vibration sensor Generates voltage between its 2 leads Sensitive! Needs resistor in parallel
• Serial Monitor:Serial.begin(9600) to start communicationSerial.println(“msg”) to print to monitor
MAKE: Calibrate Sensor• Connect sensor to analog pin
with 1M resistor in parallel
• Open skeleton_sensor_calibrate• Use Serial Monitor to report value from sensor, find out
minimum value produced by a knock THRESHOLD• Modify delay between readings so it won’t ignore two
quick knocks or give you extra knocks DEBOUNCE
CHALLENGE:• Add LED to indicate knock
Pulse Width Modulation• Duty cycle = percentage of time signal is positive
in square wave• Min-Max voltage: 0 – 5v
Min-Max Arduino mapping: 0 – 255• PWM pins have a ~ on Arduino
10% average
50% average
90% average
DC Motors
Current through in 1 direction turns them in 1 direction
More voltage = More speed, control?Use electronically controlled switch (transistor)
between motor and batteriesUse PWM pin to control switch
• They draw more current than USB/Arduino can supply (40mA per pin) so need another power supply: batteries / wall-wart
Motor
PWM
6v
Servo Motors
Control signal uses PWM, pulse width = position
3 wires: power = red ground = brown control = yellow
• Moves to desired position and stops, limited range of 180° in 2 directions
• Control circuit + potentiometer + DC motor + position shaft with gears
Servo Library
MAKE: Calibrate Motor
• #include <Servo.h>• Create object• Object.attach(pin)• Object.write(position) *in degrees
• Connect Servo motor to PWM pin, power and ground• Open skeleton_motor_calibrate• Find “opened” and “closed” positions by sweeping shaft • **Don’t disconnect sensor, will use later!
MAKE: Secret Knock Detector• Secret knock is stored as array of time intervals• Validation logic: compare time intervals within allowed error
• Start with skeleton_basic_door_knock, using serial monitor• When that works add servo movement instead of printing• Verify code with staff and try the BIG DOOR!
Useful Links
Original Instructables project http://www.instructables.com/id/Secret-Knock-Detecting-
Door-Lock/
MAKE projects http://makezine.com/arduino/http://makezine.com/category/electronics/arduino/?
post_type=projects
Jeremy Blum Tutorials (#5: motors and transistors)http://www.jeremyblum.com/category/arduino-tutorials/
