BreadBoard + Jumper Wires<\/td> –<\/td> for connections<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<\/div>\n\n\n\n
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Code Logic<\/h2>\n\n\n\nEntire Source Code<\/summary>\n#include <Servo.h>\n#include <LiquidCrystal_I2C.h>\n\nLiquidCrystal_I2C lcd(0x20, 16, 2);\nServo arm;\n\n\/\/pins\nconst int ultrasonic_pin = 9;\nconst int servo_pin = 6;\nconst int buzzer_pin = 3;\n\n\/\/window\nconst int min_dist = 60;\nconst int max_dist = 150;\n\n\/\/beat\nfloat lastDistance = 0;\nfloat lastVelocity = 0;\nbool approaching = false;\n\nunsigned long lastBeat = 0;\nconst unsigned long min_beat_gap = 250;\n\n\/\/BPM\nunsigned long history[4] = {0};\nint Pos = 0;\nbool Full = false;\nfloat bpm = 0;\n\n\/\/Notes\nconst int notes[] = {196,220,247,294,330,392,440,494};\nconst int note_count = sizeof(notes) \/ sizeof(int);\n\nvoid setup() {\n Serial.begin(115200);\n \n pinMode(buzzer_pin, OUTPUT);\n digitalWrite(buzzer_pin, LOW);\n \n \/\/setup lcd\n lcd.init();\n lcd.backlight();\n lcd.clear();\n \n \/\/reset servo position\n arm.attach(servo_pin);\n arm.write(90);\n \n randomSeed(analogRead(A0));\n \/\/start timer\n lastBeat = millis();\n\n}\n\nvoid loop(){\n unsigned long now = millis();\n \n \/\/Read distance\n float dist = readDistanceCM();\n \/\/positive value, continues\n bool valid = (dist>0);\n \n if (valid){\n \/\/servo follows hand\n arm.write(distanceToAngle(dist));\n }\n \n \/\/Detect beat\n float velocity = lastDistance - dist;\n \/\/within the window that we defined\n bool inRange = (dist >= min_dist && dist <= max_dist);\n\n \/\/valid hand movement, continues\n if (inRange && velocity > 0.4) {\n approaching = true;\n }\n \n \/\/for detecting hand movement coming back\n bool reversed = (lastVelocity > 0 && velocity < 0);\n \n if (valid && approaching && reversed && (now - lastBeat > min_beat_gap)){\n triggerBeat();\n record(now);\n approaching = false;\n }\n \n lastVelocity = velocity;\n lastDistance = dist;\n \n \/\/lcd\n static unsigned long lastLCD = 0;\n if (now - lastLCD > 200) {\n lastLCD = now;\n updateLCD(valid ? dist : -1, bpm);\n }\n \n delay(15);\n\n}\n\n\nfloat readDistanceCM() {\n pinMode(ultrasonic_pin, OUTPUT);\n digitalWrite(ultrasonic_pin, LOW);\n delayMicroseconds(2);\n digitalWrite(ultrasonic_pin, HIGH);\n delayMicroseconds(10);\n digitalWrite(ultrasonic_pin, LOW);\n \n \/\/echo\n pinMode(ultrasonic_pin, INPUT);\n unsigned long dur = pulseIn(ultrasonic_pin, HIGH, 15000);\n \n if (dur==0) return -1;\n \n float cm = dur \/ 58.0;\n if (cm < 2 || cm > 400) return -1;\n \n return cm;\n}\n\n\nint distanceToAngle(float cm) {\n \/\/detect distance inside the window\n if (cm < min_dist) cm = min_dist;\n if (cm > max_dist) cm = max_dist;\n \n \/\/convert distance to servo angle\n float t = (cm - min_dist) \/ (max_dist - min_dist);\n return 35 + (int)(t*(120-35));\n}\n\nvoid triggerBeat() {\n int note = notes[random(note_count)];\n tone(buzzer_pin, note, 120);\n lastBeat = millis();\n}\n\nvoid record(unsigned long now) {\n unsigned long x = now - lastBeat;\n history[Pos] = x;\n Pos = (Pos + 1) % 4;\n \n \/\/true once we have stored 4 intervals\n if (Pos == 0) Full = true;\n \n if (Full) {\n unsigned long sum = 0;\n for (int i=0; i<4; i++) {\n sum += history[i];\n }\n \n float avg = sum \/ 4.0;\n bpm = 60000.0 \/ avg;\n \n }\n}\n\nvoid updateLCD(float dist, float bpm) {\n \/\/print distance\n lcd.setCursor(0, 0);\n if (dist < 0) {\n lcd.print(\"Dist: -- \");\n } else {\n lcd.print(\"Dist: \");\n lcd.print((int)dist);\n lcd.print(\"cm \");\n }\n\n lcd.setCursor(0, 1);\n lcd.print(\"BPM: \");\n if (bpm > 0) lcd.print((int)bpm);\n else lcd.print(\"--\");\n lcd.print(\" \");\n}<\/code><\/pre>\n<\/details>\n\n\n\n\nRead distance: The ultrasonic sensor measures hand distance.<\/li>\n\n\n\n Filter Noise: A smoothing algorithm for the ultrasonic sensor to remove inconsistent values that might affect consistency<\/li>\n\n\n\n Detect Beat: If the hand moves toward the sensor and then reverses direction quickly, then it’s considered to a beat.<\/li>\n\n\n\n Play Beat: After a beat is detected, the system will react to it by playing a random musical note using tone(), and move the servo slightly as a drum tap.<\/li>\n\n\n\n Calculate BPM: The program stores the last few beat intervals and averages them.<\/li>\n\n\n\n Display Data: The LCD continuously updates to show distance and BPM.<\/li>\n<\/ol>\n\n\n\nCode Explanation<\/h2>\n\n\n\nvoid setup() {\n Serial.begin(115200);\n \n pinMode(buzzer_pin, OUTPUT);\n digitalWrite(buzzer_pin, LOW);\n \n \/\/setup lcd\n lcd.init();\n lcd.backlight();\n lcd.clear();\n \n \/\/reset servo position\n arm.attach(servo_pin);\n arm.write(90);\n \n randomSeed(analogRead(A0));\n \/\/start timer\n lastBeat = millis();\n\n}<\/code><\/pre>\n\n\n\nThe program starts with the setup() function, which runs once when the program is uploaded to Arduino. It includes all of the libraries needed and initializes all the variables.<\/p>\n\n\n\n
Serial.begin(115200);<\/code><\/pre>\n\n\n\nThis line starts a serial port at 115200, which acts as the console and allows Arduino to send debugging messages. In addition, pinMode() sets up the buzzer’s pin so it can send sound signals. The parameters of it are the pin number and the mode (output \/ input).<\/p>\n\n\n\n
diginalWrite(<pin>, LOW) turns off the buzzer at the start so it doesn’t make any sound when the program starts. With digitalWrite(), you are able to either set it as High (5V) or Low (0V).<\/p>\n\n\n\n
Afterwards, the LCD display get initialized. And the servo is configured at a specific pin.<\/p>\n\n\n\n
The code now proceeds to the loop() function which runs over and over again.<\/p>\n\n\n\n
unsigned long nowMs = millis();<\/code><\/pre>\n\n\n\nmillis() is a built in function that returns the number of milliseconds since the program started running. And in this case, it is assigned and stored in a variable called nowMs, and is used throughout the loop for timing things like detecting the beat and stuff.<\/p>\n\n\n\n
\/\/Read distance\n float dist = readDistanceCM();\n \/\/positive value, continues\n bool valid = (dist>0);\n\n\/\/read distance function\nfloat readDistanceCM() {\n pinMode(ultrasonic_pin, OUTPUT);\n digitalWrite(ultrasonic_pin, LOW);\n delayMicroseconds(2);\n digitalWrite(ultrasonic_pin, HIGH);\n delayMicroseconds(10);\n digitalWrite(ultrasonic_pin, LOW);\n \n \/\/echo\n pinMode(ultrasonic_pin, INPUT);\n unsigned long dur = pulseIn(ultrasonic_pin, HIGH, 15000);\n \n if (dur==0) return -1;\n \n float cm = dur \/ 58.0;\n if (cm < 2 || cm > 400) return -1;\n \n return cm;\n}<\/code><\/pre>\n\n\n\nThis section is in charge of reading the distance from the ultrasonic sensor and smoothening the data received. This is achieved by first creating a floating variable and calling the readDistanceCM() function to store the distance returned inside it. Afterwards, a boolean variable is created to check if the reading make sense. And if valid, the distance is passed on to convert it to an angle.<\/p>\n\n\n\n
\/\/Servo follows\n if (valid) {\n int targetAngle = distanceToAngle(emaDist);\n arm.write(targetAngle);\n }\n\n\/\/function to convert distance to angle\nint distanceToAngle(float cm) {\n \/\/detect distance inside the window\n if (cm < min_dist) cm = min_dist;\n if (cm > max_dist) cm = max_dist;\n \n \/\/convert distance to servo angle\n float t = (cm - min_dist) \/ (max_dist - min_dist);\n return 35 + (int)(t*(120-35));\n}<\/code><\/pre>\n\n\n\nIf the distance is valid, it converts it to an angle that can be passed on to the servo using the distanceToAngle function.<\/p>\n\n\n\n
\/\/Detect beat\n float velocity = lastDistance - dist;\n \/\/within the window that we defined\n bool inRange = (dist >= min_dist && dist <= max_dist);\n\n \/\/valid hand movement, continues\n if (inRange && velocity > 0.4) {\n approaching = true;\n }<\/code><\/pre>\n\n\n\nThis section is responsible for detecting whether the hand is moving toward the sensor fast enough to count as a beat gesture.<\/p>\n\n\n\n
dist is the distance from the ultrasonic sensor. lastDistance is the previous loop’s distance, and is stored to compare how much the distance changed since then. In other words, if the hand moves quickly, the difference between those two values becomes bigger.<\/p>\n\n\n\n
velocity = lastDistance - dist;<\/code><\/pre>\n\n\n\nTherefore, the formula above gives an estimate of how fast the hand is moving. If the hand moves closer to the sensor, then emaDist (current distance) becomes smaller, lastDistance – dist becomes positive, and this represents positive velocity, vice versa.<\/p>\n\n\n\n
\/\/within the window that we defined\n bool inRange = (dist >= min_dist && dist <= max_dist);\n\n \/\/valid hand movement, continues\n if (inRange && velocity > 0.4) {\n approaching = true;\n }<\/code><\/pre>\n\n\n\nThe window min and max defines the detection zone that we actually consider about, if the hand isn’t in this zone, we ignore the movement, and this is used to prevent false triggers. And approaching is simply a boolean variable that is true when the hand is inside this distance zone.<\/p>\n\n\n\n
if (valid && approaching && reversed && (now - lastBeat > min_beat_gap)){\n triggerBeat();\n record(now);\n approaching = false;\n }<\/code><\/pre>\n\n\n\nFinally, the if statement considers whether the hand is inside the valid distance zone and is moving toward the sensor fast enough, if so, it triggers a beat by calling that function.<\/p>\n\n\n\n
float readDistanceCM() {\n pinMode(ultrasonic_pin, OUTPUT);\n digitalWrite(ultrasonic_pin, LOW);\n delayMicroseconds(2);\n digitalWrite(ultrasonic_pin, HIGH);\n delayMicroseconds(10);\n digitalWrite(ultrasonic_pin, LOW);\n \n \/\/echo\n pinMode(ultrasonic_pin, INPUT);\n unsigned long dur = pulseIn(ultrasonic_pin, HIGH, 15000);\n \n if (dur==0) return -1;\n \n float cm = dur \/ 58.0;\n if (cm < 2 || cm > 400) return -1;\n \n return cm;\n}<\/code><\/pre>\n\n\n\nNext up, this function is in charge of calculating the distance from the hand. The logic of it is to first send a short ultrasonic pulse, and wait for the echo to return. And by using this data, it is able to convert that time into a distance measurement.<\/p>\n\n\n\n
float dist = readDistanceCM();<\/code><\/pre>\n\n\n\nWe have actually mentioned it previously, and called it to store it inside the dist variable.<\/p>\n\n\n\n
pinMode(ULTRA_PIN, OUTPUT);\ndigitalWrite(ULTRA_PIN, LOW);\ndelayMicroseconds(2);\ndigitalWrite(ULTRA_PIN, HIGH);\ndelayMicroseconds(10);\ndigitalWrite(ULTRA_PIN, LOW);<\/code><\/pre>\n\n\n\nThis line first allows assigns a pin and mode for the sensor. And create a pulse starting with low for 2 microseconds, high for 10 microseconds, and back to low again. <\/p>\n\n\n\n
pinMode(ULTRA_PIN, INPUT);<\/code><\/pre>\n\n\n\nAfter that, it immediately switched to input mode to listen for the echo returning.<\/p>\n\n\n\n
unsigned long dur = pulseIn(ULTRA_PIN, HIGH, 15000UL);\nfloat cm = dur \/ 58.0;<\/code><\/pre>\n\n\n\nFinally, this standard formula converts the echo received into distance in centimeters.<\/p>\n\n\n\n
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Above, I have explained all the essential parts of the code. Most of the program\u2019s logic is organized inside the main loop, but to keep the code cleaner and easier, I moved any repeated or commonly used operations into separate functions.
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