Embedded Files
Joe Aloisio
Secret Knock
Description - My final project is a door lock that listens for your personalized knock. The lock uses an arduino board and a piezo speaker and will not unlock the door unless the specific pattern is used as a knock.
Pictures of the Beast (pre-production) -
Circuit Diagram -
Arduino Program -
/* Detects patterns of knocks and triggers a motor to unlock
it if the pattern is correct.
By Steve Hoefer http://grathio.com
Version 0.1.09.20.09
Licensed under Creative Commons Attribution-Noncommercial-Share Alike 3.0
http://creativecommons.org/licenses/by-nc-sa/3.0/us/
(In short: Do what you want, just be sure to include this line and the four above it, and don't sell it or use it in anything you sell without contacting me.)
Analog Pin 0: Piezo speaker (connected to ground with 1M pulldown resistor)
Digital Pin 2: Switch to enter a new code. Short this to enter programming mode.
Digital Pin 3: DC gear reduction motor attached to the lock. (Or a motor controller or a solenoid or other unlocking mechanisim.)
Digital Pin 4: Red LED.
Digital Pin 5: Green LED.
Update: Nov 09 09: Fixed red/green LED error in the comments. Code is unchanged.
Update: Nov 20 09: Updated handling of programming button to make it more intuitive, give better feedback.
*/
// Pin definitions
const int knockSensor = 0; // Piezo sensor on pin 0.
const int programSwitch = 2; // If this is high we program a new code.
const int lockMotor = 3; // Gear motor used to turn the lock.
const int redLED = 4; // Status LED
const int greenLED = 5; // Status LED
// Tuning constants. Could be made vars and hoooked to potentiometers for soft configuration, etc.
const int threshold = 3; // Minimum signal from the piezo to register as a knock
const int rejectValue = 25; // If an individual knock is off by this percentage of a knock we don't unlock..
const int averageRejectValue = 15; // If the average timing of the knocks is off by this percent we don't unlock.
const int knockFadeTime = 150; // milliseconds we allow a knock to fade before we listen for another one. (Debounce timer.)
const int lockTurnTime = 650; // milliseconds that we run the motor to get it to go a half turn.
const int maximumKnocks = 20; // Maximum number of knocks to listen for.
const int knockComplete = 1200; // Longest time to wait for a knock before we assume that it's finished.
// Variables.
int secretCode[maximumKnocks] = {50, 25, 25, 50, 100, 50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; // Initial setup: "Shave and a Hair Cut, two bits."
int knockReadings[maximumKnocks]; // When someone knocks this array fills with delays between knocks.
int knockSensorValue = 0; // Last reading of the knock sensor.
int programButtonPressed = false; // Flag so we remember the programming button setting at the end of the cycle.
void setup() {
pinMode(knockSensor, OUTPUT);
pinMode(lockMotor, OUTPUT);
pinMode(redLED, OUTPUT);
pinMode(greenLED, OUTPUT);
pinMode(programSwitch, INPUT);
Serial.begin(9600); // Uncomment the Serial.bla lines for debugging.
Serial.println("Program start."); // but feel free to comment them out after it's working right.
digitalWrite(greenLED, HIGH); // Green LED on, everything is go.
}
void loop() {
// Listen for any knock at all.
knockSensorValue = analogRead(knockSensor);
if (digitalRead(programSwitch)==HIGH){ // is the program button pressed?
programButtonPressed = true; // Yes, so lets save that state
digitalWrite(redLED, HIGH); // and turn on the red light too so we know we're programming.
} else {
programButtonPressed = false;
digitalWrite(redLED, LOW);
}
if (knockSensorValue >=threshold){
listenToSecretKnock();
}
}
// Records the timing of knocks.
void listenToSecretKnock(){
Serial.println("knock starting");
int i = 0;
// First lets reset the listening array.
for (i=0;i<maximumKnocks;i++){
knockReadings[i]=0;
}
int currentKnockNumber=0; // Incrementer for the array.
int startTime=millis(); // Reference for when this knock started.
int now=millis();
digitalWrite(greenLED, LOW); // we blink the LED for a bit as a visual indicator of the knock.
if (programButtonPressed==true){
digitalWrite(redLED, LOW); // and the red one too if we're programming a new knock.
}
delay(knockFadeTime); // wait for this peak to fade before we listen to the next one.
digitalWrite(greenLED, HIGH);
if (programButtonPressed==true){
digitalWrite(redLED, HIGH);
}
do {
//listen for the next knock or wait for it to timeout.
knockSensorValue = analogRead(knockSensor);
if (knockSensorValue >=threshold){ //got another knock...
//record the delay time.
Serial.println("knock.");
now=millis();
knockReadings[currentKnockNumber] = now-startTime;
currentKnockNumber ++; //increment the counter
startTime=now;
// and reset our timer for the next knock
digitalWrite(greenLED, LOW);
if (programButtonPressed==true){
digitalWrite(redLED, LOW); // and the red one too if we're programming a new knock.
}
delay(knockFadeTime); // again, a little delay to let the knock decay.
digitalWrite(greenLED, HIGH);
if (programButtonPressed==true){
digitalWrite(redLED, HIGH);
}
}
now=millis();
//did we timeout or run out of knocks?
} while ((now-startTime < knockComplete) && (currentKnockNumber < maximumKnocks));
//we've got our knock recorded, lets see if it's valid
if (programButtonPressed==false){ // only if we're not in progrmaing mode.
if (validateKnock() == true){
triggerDoorUnlock();
} else {
Serial.println("Secret knock failed.");
digitalWrite(greenLED, LOW); // We didn't unlock, so blink the red LED as visual feedback.
for (i=0;i<4;i++){
digitalWrite(redLED, HIGH);
delay(100);
digitalWrite(redLED, LOW);
delay(100);
}
digitalWrite(greenLED, HIGH);
}
} else { // if we're in programming mode we still validate the lock, we just don't do anything with the lock
validateKnock();
// and we blink the green and red alternately to show that program is complete.
Serial.println("New lock stored.");
digitalWrite(redLED, LOW);
digitalWrite(greenLED, HIGH);
for (i=0;i<3;i++){
delay(100);
digitalWrite(redLED, HIGH);
digitalWrite(greenLED, LOW);
delay(100);
digitalWrite(redLED, LOW);
digitalWrite(greenLED, HIGH);
}
}
}
// Runs the motor (or whatever) to unlock the door.
void triggerDoorUnlock(){
Serial.println("Door unlocked!");
int i=0;
// turn the motor on for a bit.
digitalWrite(lockMotor, HIGH);
digitalWrite(greenLED, HIGH); // And the green LED too.
delay (lockTurnTime); // Wait a bit.
digitalWrite(lockMotor, LOW); // Turn the motor off.
// Blink the green LED a few times for more visual feedback.
for (i=0; i < 5; i++){
digitalWrite(greenLED, LOW);
delay(100);
digitalWrite(greenLED, HIGH);
delay(100);
}
}
// Sees if our knock matches the secret.
// returns true if it's a good knock, false if it's not.
// todo: break it into smaller functions for readability.
boolean validateKnock(){
int i=0;
// simplest check first: Did we get the right number of knocks?
int currentKnockCount = 0;
int secretKnockCount = 0;
int maxKnockInterval = 0; // We use this later to normalize the times.
for (i=0;i<maximumKnocks;i++){
if (knockReadings[i] > 0){
currentKnockCount++;
}
if (secretCode[i] > 0){ //todo: precalculate this.
secretKnockCount++;
}
if (knockReadings[i] > maxKnockInterval){ // collect normalization data while we're looping.
maxKnockInterval = knockReadings[i];
}
}
// If we're recording a new knock, save the info and get out of here.
if (programButtonPressed==true){
for (i=0;i<maximumKnocks;i++){ // normalize the times
secretCode[i]= map(knockReadings[i],0, maxKnockInterval, 0, 100);
}
// And flash the lights in the recorded pattern to let us know it's been programmed.
digitalWrite(greenLED, LOW);
digitalWrite(redLED, LOW);
delay(1000);
digitalWrite(greenLED, HIGH);
digitalWrite(redLED, HIGH);
delay(50);
for (i = 0; i < maximumKnocks ; i++){
digitalWrite(greenLED, LOW);
digitalWrite(redLED, LOW);
// only turn it on if there's a delay
if (secretCode[i] > 0){
delay( map(secretCode[i],0, 100, 0, maxKnockInterval)); // Expand the time back out to what it was. Roughly.
digitalWrite(greenLED, HIGH);
digitalWrite(redLED, HIGH);
}
delay(50);
}
return false; // We don't unlock the door when we are recording a new knock.
}
if (currentKnockCount != secretKnockCount){
return false;
}
/* Now we compare the relative intervals of our knocks, not the absolute time between them.
(ie: if you do the same pattern slow or fast it should still open the door.)
This makes it less picky, which while making it less secure can also make it
less of a pain to use if you're tempo is a little slow or fast.
*/
int totaltimeDifferences=0;
int timeDiff=0;
for (i=0;i<maximumKnocks;i++){ // Normalize the times
knockReadings[i]= map(knockReadings[i],0, maxKnockInterval, 0, 100);
timeDiff = abs(knockReadings[i]-secretCode[i]);
if (timeDiff > rejectValue){ // Individual value too far out of whack
return false;
}
totaltimeDifferences += timeDiff;
}
// It can also fail if the whole thing is too inaccurate.
if (totaltimeDifferences/secretKnockCount>averageRejectValue){
return false;
}
return true;
}
Problems - The biggest problem that I encountered was finding the right parts to build the project. First of all, I waited too long to order the motor and had to try and buy one through a store. This was 100% my own fault but to make matters worse, every Radioshack in Southeast Michigan decided that they no longer wanted to sell components (or the components i needed) for the arduino. I have been trying to find a gear reduction motor that will fit inside of a 1/2 inch PVC pipe and have enough torque to turn a dead lock on an ordinary door. Tougher task than what was expected by far. The next BIG issue was finding a specific PVC pipe part that unfortunantely no hardware stores feel necessary to carry?! The part in question is a 5-way PVC pipe connector. It is used to hold the motor in place to turn the lock on the door, and also to connect the entire project together. Needless to say, it was a pretty important part. Maybe i was just being lazy but i also felt that i was in a little over my head, with all things included. The project that i chose required a pretty extensive knowledge of a lot of things that i didnt know about previously. I do feel though that i came out of this with learning some pretty cool stuff that i would have had no idea of in the past.
What if? - I think if i could go back and do this again i would definitely change a few things with the design of the project and also with the code and internal things. To cosmetically fix the project i would have change the design of the PVC pipe and possibly used a smaller, more efficient device. With almost two feet of pipe, you can imagine that it looks somewhat out of the ordinary attached to the inside of your door. I kind of invisioned something more along the lines of a small box that fit over the entire lock as opposed to over the door as well. The box would sit directly over the lock and the secret knock would be used to lock, and also unlock the door. This would allow the person that had the device to keep it on their door without it looking out of the ordinary, and would also allow for the more artistic folk the opportunity to better decorate, and enhance the project. The main thing that i would like to change about the code itself would be to implement some sort of 'sleep' mode. A minor issue involving the project is that the battery is continually giving power to the arduino no matter what is happening. If a sleep mode could be added, it would be more eco-friendly and less expensive. With the sleep mode, im sure a 9v battery would last for a little over a millenium due to the fact that when it does run, it runs for only a short period of time.
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