Hi guys, first time posting in this forum. 
Trying out this fall detection code for my own understanding.
The code seems to be working, I'm able to detect falls and send an SMS, although its inconsistent. I've been trying to crack my head understanding this code. Heres the code, the questions are at the bottom. Hoping you guys can help out, thanks alot!
Full Code:
#include <Wire.h>
#include <ESP8266WiFi.h>
const int MPU_addr=0x68; // I2C address of the MPU-6050
int16_t AcX,AcY,AcZ,Tmp,GyX,GyY,GyZ;
float ax=0, ay=0, az=0, gx=0, gy=0, gz=0;
boolean fall = false; //stores if a fall has occurred
boolean trigger1=false; //stores if first trigger (lower threshold) has occurred
boolean trigger2=false; //stores if second trigger (upper threshold) has occurred
boolean trigger3=false; //stores if third trigger (orientation change) has occurred
byte trigger1count=0; //stores the counts past since trigger 1 was set true
byte trigger2count=0; //stores the counts past since trigger 2 was set true
byte trigger3count=0; //stores the counts past since trigger 3 was set true
int angleChange=0;
// WiFi network info.
const char *ssid = "..."; // Enter your WiFi Name
const char *pass = "...."; // Enter your WiFi Password
void send_event(const char *event);
const char *host = "maker.ifttt.com";
const char *privateKey = "...";
void setup(){
Serial.begin(115200);
Wire.begin();
Wire.beginTransmission(MPU_addr);
Wire.write(0x6B); // PWR_MGMT_1 register
Wire.write(0); // set to zero (wakes up the MPU-6050)
Wire.endTransmission(true);
Serial.println("Wrote to IMU");
Serial.println("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, pass);
while (WiFi.status() != WL_CONNECTED)
{
delay(500);
Serial.print("."); // print ... till not connected
}
Serial.println("");
Serial.println("WiFi connected");
}
void loop(){
mpu_read();
ax = (AcX-2050)/16384.00;
ay = (AcY-77)/16384.00;
az = (AcZ-1947)/16384.00;
gx = (GyX+270)/131.07;
gy = (GyY-351)/131.07;
gz = (GyZ+136)/131.07;
// calculating Amplitute vector for 3 axis
float Raw_Amp = pow(pow(ax,2)+pow(ay,2)+pow(az,2),0.5);
int Amp = Raw_Amp * 10; // Mulitiplied by 10 bcz values are between 0 to 1
Serial.println(Amp);
if (Amp<=2 && trigger2==false){ //if AM breaks lower threshold (0.4g)
trigger1=true;
Serial.println("TRIGGER 1 ACTIVATED");
}
if (trigger1==true){
trigger1count++;
if (Amp>=12){ //if AM breaks upper threshold (3g)
trigger2=true;
Serial.println("TRIGGER 2 ACTIVATED");
trigger1=false; trigger1count=0;
}
}
if (trigger2==true){
trigger2count++;
angleChange = pow(pow(gx,2)+pow(gy,2)+pow(gz,2),0.5); Serial.println(angleChange);
if (angleChange>=30 && angleChange<=400){ //if orientation changes by between 80-100 degrees
trigger3=true; trigger2=false; trigger2count=0;
Serial.println(angleChange);
Serial.println("TRIGGER 3 ACTIVATED");
}
}
if (trigger3==true){
trigger3count++;
if (trigger3count>=10){
angleChange = pow(pow(gx,2)+pow(gy,2)+pow(gz,2),0.5);
//delay(10);
Serial.println(angleChange);
if ((angleChange>=0) && (angleChange<=10)){ //if orientation changes remains between 0-10 degrees
fall=true; trigger3=false; trigger3count=0;
Serial.println(angleChange);
}
else{ //user regained normal orientation
trigger3=false; trigger3count=0;
Serial.println("TRIGGER 3 DEACTIVATED");
}
}
}
if (fall==true){ //in event of a fall detection
Serial.println("FALL DETECTED");
send_event("fall_detect");
fall=false;
}
if (trigger2count>=6){ //allow 0.5s for orientation change
trigger2=false; trigger2count=0;
Serial.println("TRIGGER 2 DECACTIVATED");
}
if (trigger1count>=6){ //allow 0.5s for AM to break upper threshold
trigger1=false; trigger1count=0;
Serial.println("TRIGGER 1 DECACTIVATED");
}
delay(100);
}
void mpu_read(){
Wire.beginTransmission(MPU_addr);
Wire.write(0x3B); // starting with register 0x3B (ACCEL_XOUT_H)
Wire.endTransmission(false);
Wire.requestFrom(MPU_addr,14,true); // request a total of 14 registers
AcX=Wire.read()<<8|Wire.read(); // 0x3B (ACCEL_XOUT_H) & 0x3C (ACCEL_XOUT_L)
AcY=Wire.read()<<8|Wire.read(); // 0x3D (ACCEL_YOUT_H) & 0x3E (ACCEL_YOUT_L)
AcZ=Wire.read()<<8|Wire.read(); // 0x3F (ACCEL_ZOUT_H) & 0x40 (ACCEL_ZOUT_L)
Tmp=Wire.read()<<8|Wire.read(); // 0x41 (TEMP_OUT_H) & 0x42 (TEMP_OUT_L)
GyX=Wire.read()<<8|Wire.read(); // 0x43 (GYRO_XOUT_H) & 0x44 (GYRO_XOUT_L)
GyY=Wire.read()<<8|Wire.read(); // 0x45 (GYRO_YOUT_H) & 0x46 (GYRO_YOUT_L)
GyZ=Wire.read()<<8|Wire.read(); // 0x47 (GYRO_ZOUT_H) & 0x48 (GYRO_ZOUT_L)
}
void send_event(const char *event)
{
Serial.print("Connecting to ");
Serial.println(host);
// Use WiFiClient class to create TCP connections
WiFiClient client;
const int httpPort = 80;
if (!client.connect(host, httpPort)) {
Serial.println("Connection failed");
return;
}
// We now create a URI for the request
String url = "/trigger/";
url += event;
url += "/with/key/";
url += privateKey;
Serial.print("Requesting URL: ");
Serial.println(url);
// This will send the request to the server
client.print(String("GET ") + url + " HTTP/1.1\r\n" +
"Host: " + host + "\r\n" +
"Connection: close\r\n\r\n");
while(client.connected())
{
if(client.available())
{
String line = client.readStringUntil('\r');
Serial.print(line);
} else {
// No data yet, wait a bit
delay(50);
};
}
Serial.println();
Serial.println("closing connection");
client.stop();
}
Output From Serial Monitor:
When Still On Flat Ground : Consistently at 9... occasionally 8
Attached an Image with the outputs I've gotten.
Question:
1) Why is the output 9 when still?
I would assume that it should be 0g, I've deducted the Ax,Ay,Az,Gx,Gy and Gz from the offsets and divided by its respective sensitivities. I've calibrated my MPU6050 sensors and gotten the offsets.
2) How does one know that this Amp (12) is 3g?
if (Amp>=12){ //if AM breaks upper threshold (3g)
trigger2=true;
Serial.println("TRIGGER 2 ACTIVATED");
trigger1=false; trigger1count=0;
}
3) How does one know that the angle is between 80-100 degrees, when its angleChange is 30 to 400?
angleChange = pow(pow(gx,2)+pow(gy,2)+pow(gz,2),0.5); Serial.println(angleChange);
if (angleChange>=30 && angleChange<=400){ //if orientation changes by between 80-100 degrees
trigger3=true; trigger2=false; trigger2count=0;
Serial.println(angleChange);
Serial.println("TRIGGER 3 ACTIVATED");
}
Many thanks! I'm new at this, trying hard to learn codes and doing projects. Just having difficulty dissecting whats happening here 
Would appreciate any help!
