1. Secret Door Knock Detector1
Arduino Tutorial 2:
Secret Door Knock Detector

2. Agenda Sensor Review MAKE: calibrate sensor PWM Motors2
Agenda
Sensor Review
MAKE: calibrate sensor
PWM
Motors
MAKE: calibrate motor
Validation algorithm
MAKE: Secret Knock Detector
Links

3. 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 communication
Serial.println(“msg”) to print to monitor

4. 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

5. 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

6. DC Motors
They draw more current than USB/Arduino can supply (40mA per pin) so need another power supply: batteries / wall-wart
Current through in 1 direction turns them in 1 direction
Motor
PWM 6v
More voltage = More speed, control?
Use electronically controlled switch (transistor) between motor and batteries
Use PWM pin to control switch

7. Servo Motors
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
Control signal uses PWM, pulse width = position

8. MAKE: Calibrate Motor Servo Library
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!
Servo Library
#include <Servo.h>
Create object
Object.attach(pin)
Object.write(position) *in degrees

9. 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!

10. Useful Links http://www.jeremyblum.com/category/arduino-tutorials/
Original Instructables project
MAKE projects
Jeremy Blum Tutorials (#5: motors and transistors)

11. academics@ieee.concordia.ca ieee.concordia.ca
Questions? Comments? Suggestions?
ieee.concordia.ca