Salve a tutti!
Sto provando a realizzare un "mouse" con arduino. Questo mouse prevede lo spostamento del cursore sulla base del movimento del braccio umano. Per poter far questo mi son documentato e ho trovato l'MPU6050, che può fare sia da accelerometro e sia da giroscopio. Ho scelto di usare l'accelerometro in questo caso. Tuttavia ho riscontrato dei problemi con l'MPU6050 riguardo la calibrazione dell'accelerometro, per quanto riguarda la calibrazione ho usato questo sketch:
#include "I2Cdev.h"
#include "MPU6050.h"
#include "Wire.h"
/////////////////////////////////// CONFIGURATION /////////////////////////////
//Change this 3 variables if you want to fine tune the skecth to your needs.
int buffersize=1000; //Amount of readings used to average, make it higher to get more precision but sketch will be slower (default:1000)
int acel_deadzone=8; //Acelerometer error allowed, make it lower to get more precision, but sketch may not converge (default:8)
int giro_deadzone=1; //Giro error allowed, make it lower to get more precision, but sketch may not converge (default:1)
// default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for InvenSense evaluation board)
// AD0 high = 0x69
//MPU6050 accelgyro;
MPU6050 accelgyro(0x68); // <-- use for AD0 high
int16_t ax, ay, az,gx, gy, gz;
int mean_ax,mean_ay,mean_az,mean_gx,mean_gy,mean_gz,state=0;
int ax_offset,ay_offset,az_offset,gx_offset,gy_offset,gz_offset;
/////////////////////////////////// SETUP ////////////////////////////////////
void setup() {
// join I2C bus (I2Cdev library doesn't do this automatically)
Wire.begin();
// initialize serial communication
Serial.begin(115200);
// initialize device
accelgyro.initialize();
// wait for ready
while (Serial.available() && Serial.read()); // empty buffer
while (!Serial.available()){
Serial.println(F("Send any character to start sketch.\n"));
delay(1500);
}
while (Serial.available() && Serial.read()); // empty buffer again
// start message
Serial.println("\nMPU6050 Calibration Sketch");
delay(2000);
Serial.println("\nYour MPU6050 should be placed in horizontal position, with package letters facing up. \nDon't touch it until you see a finish message.\n");
delay(3000);
// verify connection
Serial.println(accelgyro.testConnection() ? "MPU6050 connection successful" : "MPU6050 connection failed");
delay(1000);
// reset offsets
accelgyro.setXAccelOffset(0);
accelgyro.setYAccelOffset(0);
accelgyro.setZAccelOffset(0);
accelgyro.setXGyroOffset(0);
accelgyro.setYGyroOffset(0);
accelgyro.setZGyroOffset(0);
}
/////////////////////////////////// LOOP ////////////////////////////////////
void loop() {
if (state==0){
Serial.println("\nReading sensors for first time...");
meansensors();
state++;
delay(1000);
}
if (state==1) {
Serial.println("\nCalculating offsets...");
calibration();
state++;
delay(1000);
}
if (state==2) {
meansensors();
Serial.println("\nFINISHED!");
Serial.print("\nSensor readings with offsets:\t");
Serial.print(mean_ax);
Serial.print("\t");
Serial.print(mean_ay);
Serial.print("\t");
Serial.print(mean_az);
Serial.print("\t");
Serial.print(mean_gx);
Serial.print("\t");
Serial.print(mean_gy);
Serial.print("\t");
Serial.println(mean_gz);
Serial.print("Your offsets:\t");
Serial.print(ax_offset);
Serial.print("\t");
Serial.print(ay_offset);
Serial.print("\t");
Serial.print(az_offset);
Serial.print("\t");
Serial.print(gx_offset);
Serial.print("\t");
Serial.print(gy_offset);
Serial.print("\t");
Serial.println(gz_offset);
Serial.println("\nData is printed as: acelX acelY acelZ giroX giroY giroZ");
Serial.println("Check that your sensor readings are close to 0 0 16384 0 0 0");
Serial.println("If calibration was succesful write down your offsets so you can set them in your projects using something similar to mpu.setXAccelOffset(youroffset)");
while (1);
}
}
/////////////////////////////////// FUNCTIONS ////////////////////////////////////
void meansensors(){
long i=0,buff_ax=0,buff_ay=0,buff_az=0,buff_gx=0,buff_gy=0,buff_gz=0;
while (i<(buffersize+101)){
// read raw accel/gyro measurements from device
accelgyro.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);
if (i>100 && i<=(buffersize+100)){ //First 100 measures are discarded
buff_ax=buff_ax+ax;
buff_ay=buff_ay+ay;
buff_az=buff_az+az;
buff_gx=buff_gx+gx;
buff_gy=buff_gy+gy;
buff_gz=buff_gz+gz;
}
if (i==(buffersize+100)){
mean_ax=buff_ax/buffersize;
mean_ay=buff_ay/buffersize;
mean_az=buff_az/buffersize;
mean_gx=buff_gx/buffersize;
mean_gy=buff_gy/buffersize;
mean_gz=buff_gz/buffersize;
}
i++;
delay(2); //Needed so we don't get repeated measures
}
}
void calibration(){
ax_offset=-mean_ax/8;
ay_offset=-mean_ay/8;
az_offset=(16384-mean_az)/8;
gx_offset=-mean_gx/4;
gy_offset=-mean_gy/4;
gz_offset=-mean_gz/4;
while (1){
int ready=0;
accelgyro.setXAccelOffset(ax_offset);
accelgyro.setYAccelOffset(ay_offset);
accelgyro.setZAccelOffset(az_offset);
accelgyro.setXGyroOffset(gx_offset);
accelgyro.setYGyroOffset(gy_offset);
accelgyro.setZGyroOffset(gz_offset);
meansensors();
Serial.println("...");
if (abs(mean_ax)<=acel_deadzone) ready++;
else ax_offset=ax_offset-mean_ax/acel_deadzone;
if (abs(mean_ay)<=acel_deadzone) ready++;
else ay_offset=ay_offset-mean_ay/acel_deadzone;
if (abs(16384-mean_az)<=acel_deadzone) ready++;
else az_offset=az_offset+(16384-mean_az)/acel_deadzone;
if (abs(mean_gx)<=giro_deadzone) ready++;
else gx_offset=gx_offset-mean_gx/(giro_deadzone+1);
if (abs(mean_gy)<=giro_deadzone) ready++;
else gy_offset=gy_offset-mean_gy/(giro_deadzone+1);
if (abs(mean_gz)<=giro_deadzone) ready++;
else gz_offset=gz_offset-mean_gz/(giro_deadzone+1);
if (ready==6) break;
}
}
Questo codice l'ho preso da qui.
Una volta eseguito questo codice, ottengo i valori di offset e mediante l'uso di un'altro sketch comincio a leggere i valori delle accelerazioni x y z. Nello sketch delle letture sottraggo i valori di offset ottenuti dallo sketch precedente. Durante l'esecuzione dello sketch delle letture (senza aver mosso il circuito dalla posizione in cui ho effettuato la calibrazione), non ottengo x: 0 y:0 z: 0. Ma ottengo dei valori, a mio parere, non previsti.
Sto sbagliando qualcosa?
Grazie.
Ignazio Leonardo Calogero Sperandeo.