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928b1cb Oct 23, 2013
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/*
MPL3115A2 Altitude Sensor Example
By: A.Weiss, 7/17/2012, changes Nathan Seidle Sept 23rd, 2013
License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).
Hardware Connections (Breakoutboard to Arduino):
-VCC = 3.3V
-SDA = A4
-SCL = A5
-INT pins can be left unconnected for this demo
Usage:
-Serial terminal at 9600bps
-Prints altitude in meters, temperature in degrees C, with 1/16 resolution.
-software enabled interrupt on new data, ~1Hz with full resolution
During testing, GPS with 9 sattelites reported 5393ft, sensor reported 5360ft (delta of 33ft). Very close!
*/
#include <Wire.h> // for IIC communication
#define STATUS 0x00
#define OUT_P_MSB 0x01
#define OUT_P_CSB 0x02
#define OUT_P_LSB 0x03
#define OUT_T_MSB 0x04
#define OUT_T_LSB 0x05
#define DR_STATUS 0x06
#define OUT_P_DELTA_MSB 0x07
#define OUT_P_DELTA_CSB 0x08
#define OUT_P_DELTA_LSB 0x09
#define OUT_T_DELTA_MSB 0x0A
#define OUT_T_DELTA_LSB 0x0B
#define WHO_AM_I 0x0C
#define F_STATUS 0x0D
#define F_DATA 0x0E
#define F_SETUP 0x0F
#define TIME_DLY 0x10
#define SYSMOD 0x11
#define INT_SOURCE 0x12
#define PT_DATA_CFG 0x13
#define BAR_IN_MSB 0x14
#define BAR_IN_LSB 0x15
#define P_TGT_MSB 0x16
#define P_TGT_LSB 0x17
#define T_TGT 0x18
#define P_WND_MSB 0x19
#define P_WND_LSB 0x1A
#define T_WND 0x1B
#define P_MIN_MSB 0x1C
#define P_MIN_CSB 0x1D
#define P_MIN_LSB 0x1E
#define T_MIN_MSB 0x1F
#define T_MIN_LSB 0x20
#define P_MAX_MSB 0x21
#define P_MAX_CSB 0x22
#define P_MAX_LSB 0x23
#define T_MAX_MSB 0x24
#define T_MAX_LSB 0x25
#define CTRL_REG1 0x26
#define CTRL_REG2 0x27
#define CTRL_REG3 0x28
#define CTRL_REG4 0x29
#define CTRL_REG5 0x2A
#define OFF_P 0x2B
#define OFF_T 0x2C
#define OFF_H 0x2D
#define MPL3115A2_ADDRESS 0x60 // 7-bit I2C address
long startTime;
void setup()
{
Wire.begin(); // join i2c bus
Serial.begin(57600); // start serial for output
if(IIC_Read(WHO_AM_I) == 196)
Serial.println("MPL3115A2 online!");
else
Serial.println("No response - check connections");
// Configure the sensor
setModeAltimeter(); // Measure altitude above sea level in meters
//setModeBarometer(); // Measure pressure in Pascals from 20 to 110 kPa
setOversampleRate(7); // Set Oversample to the recommended 128
enableEventFlags(); // Enable all three pressure and temp event flags
}
void loop()
{
startTime = millis();
float altitude = readAltitude();
Serial.print("Altitude(m):");
Serial.print(altitude, 2);
//altitude = readAltitudeFt();
//Serial.print(" Altitude(ft):");
//Serial.print(altitude, 2);
/*float pressure = readPressure();
Serial.print(" Pressure(Pa):");
Serial.println(pressure, 2);*/
//float temperature = readTemp();
//Serial.print(" Temp(c):");
//Serial.print(temperature, 2);
//float temperature = readTempF();
//Serial.print(" Temp(f):");
//Serial.print(temperature, 2);
Serial.print(" time diff:");
Serial.print(millis() - startTime);
Serial.println();
//delay(1);
}
//Returns the number of meters above sea level
float readAltitude()
{
toggleOneShot(); //Toggle the OST bit causing the sensor to immediately take another reading
//Wait for PDR bit, indicates we have new pressure data
int counter = 0;
while( (IIC_Read(STATUS) & (1<<1)) == 0)
{
if(++counter > 100) return(-999); //Error out
delay(1);
}
// Read pressure registers
Wire.beginTransmission(MPL3115A2_ADDRESS);
Wire.write(OUT_P_MSB); // Address of data to get
Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. THIS IS NECESSARY and not supported before Arduino V1.0.1!
Wire.requestFrom(MPL3115A2_ADDRESS, 3); // Request three bytes
//Wait for data to become available
counter = 0;
while(Wire.available() < 3)
{
if(counter++ > 100) return(-999); //Error out
delay(1);
}
byte msb, csb, lsb;
msb = Wire.read();
csb = Wire.read();
lsb = Wire.read();
toggleOneShot(); //Toggle the OST bit causing the sensor to immediately take another reading
// The least significant bytes l_altitude and l_temp are 4-bit,
// fractional values, so you must cast the calulation in (float),
// shift the value over 4 spots to the right and divide by 16 (since
// there are 16 values in 4-bits).
float tempcsb = (lsb>>4)/16.0;
float altitude = (float)( (msb << 8) | csb) + tempcsb;
return(altitude);
}
//Returns the number of feet above sea level
float readAltitudeFt()
{
return(readAltitude() * 3.28084);
}
//Reads the current pressure in Pa
//Unit must be set in barometric pressure mode
float readPressure()
{
toggleOneShot(); //Toggle the OST bit causing the sensor to immediately take another reading
//Wait for PDR bit, indicates we have new pressure data
int counter = 0;
while( (IIC_Read(STATUS) & (1<<2)) == 0)
{
if(++counter > 100) return(-999); //Error out
delay(1);
}
// Read pressure registers
Wire.beginTransmission(MPL3115A2_ADDRESS);
Wire.write(OUT_P_MSB); // Address of data to get
Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. THIS IS NECESSARY and not supported before Arduino V1.0.1!
Wire.requestFrom(MPL3115A2_ADDRESS, 3); // Request three bytes
//Wait for data to become available
counter = 0;
while(Wire.available() < 3)
{
if(counter++ > 100) return(-999); //Error out
delay(1);
}
byte msb, csb, lsb;
msb = Wire.read();
csb = Wire.read();
lsb = Wire.read();
toggleOneShot(); //Toggle the OST bit causing the sensor to immediately take another reading
// Pressure comes back as a left shifted 20 bit number
long pressure_whole = (long)msb<<16 | (long)csb<<8 | (long)lsb;
pressure_whole >>= 6; //Pressure is an 18 bit number with 2 bits of decimal. Get rid of decimal portion.
lsb &= 0b00110000; //Bits 5/4 represent the fractional component
lsb >>= 4; //Get it right aligned
float pressure_decimal = (float)lsb/4.0; //Turn it into fraction
float pressure = (float)pressure_whole + pressure_decimal;
return(pressure);
}
float readTemp()
{
toggleOneShot(); //Toggle the OST bit causing the sensor to immediately take another reading
//Wait for TDR bit, indicates we have new temp data
int counter = 0;
while( (IIC_Read(STATUS) & (1<<1)) == 0)
{
if(++counter > 100) return(-999); //Error out
delay(1);
}
// Read temperature registers
Wire.beginTransmission(MPL3115A2_ADDRESS);
Wire.write(OUT_T_MSB); // Address of data to get
Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. THIS IS NECESSARY and not supported before Arduino V1.0.1!
Wire.requestFrom(MPL3115A2_ADDRESS, 2); // Request two bytes
//Wait for data to become available
counter = 0;
while(Wire.available() < 2)
{
if(++counter > 100) return(-999); //Error out
delay(1);
}
byte msb, lsb;
msb = Wire.read();
lsb = Wire.read();
// The least significant bytes l_altitude and l_temp are 4-bit,
// fractional values, so you must cast the calulation in (float),
// shift the value over 4 spots to the right and divide by 16 (since
// there are 16 values in 4-bits).
float templsb = (lsb>>4)/16.0; //temp, fraction of a degree
float temperature = (float)(msb + templsb);
return(temperature);
}
//Give me temperature in fahrenheit!
float readTempF()
{
return((readTemp() * 9.0)/ 5.0 + 32.0); // Convert celsius to fahrenheit
}
//Sets the mode to Barometer
//CTRL_REG1, ALT bit
void setModeBarometer()
{
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting &= ~(1<<7); //Clear ALT bit
IIC_Write(CTRL_REG1, tempSetting);
}
//Sets the mode to Altimeter
//CTRL_REG1, ALT bit
void setModeAltimeter()
{
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting |= (1<<7); //Set ALT bit
IIC_Write(CTRL_REG1, tempSetting);
}
//Puts the sensor in standby mode
//This is needed so that we can modify the major control registers
void setModeStandby()
{
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting &= ~(1<<0); //Clear SBYB bit for Standby mode
IIC_Write(CTRL_REG1, tempSetting);
}
//Puts the sensor in active mode
//This is needed so that we can modify the major control registers
void setModeActive()
{
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting |= (1<<0); //Set SBYB bit for Active mode
IIC_Write(CTRL_REG1, tempSetting);
}
//Setup FIFO mode to one of three modes. See page 26, table 31
//From user jr4284
void setFIFOMode(byte f_Mode)
{
if (f_Mode > 3) f_Mode = 3; // FIFO value cannot exceed 3.
f_Mode <<= 6; // Shift FIFO byte left 6 to put it in bits 6, 7.
byte tempSetting = IIC_Read(F_SETUP); //Read current settings
tempSetting &= ~(3<<6); // clear bits 6, 7
tempSetting |= f_Mode; //Mask in new FIFO bits
IIC_Write(F_SETUP, tempSetting);
}
//Call with a rate from 0 to 7. See page 33 for table of ratios.
//Sets the over sample rate. Datasheet calls for 128 but you can set it
//from 1 to 128 samples. The higher the oversample rate the greater
//the time between data samples.
void setOversampleRate(byte sampleRate)
{
if(sampleRate > 7) sampleRate = 7; //OS cannot be larger than 0b.0111
sampleRate <<= 3; //Align it for the CTRL_REG1 register
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting &= 0b11000111; //Clear out old OS bits
tempSetting |= sampleRate; //Mask in new OS bits
IIC_Write(CTRL_REG1, tempSetting);
}
//Clears then sets the OST bit which causes the sensor to immediately take another reading
//Needed to sample faster than 1Hz
void toggleOneShot(void)
{
byte tempSetting = IIC_Read(CTRL_REG1); //Read current settings
tempSetting &= ~(1<<1); //Clear OST bit
IIC_Write(CTRL_REG1, tempSetting);
tempSetting = IIC_Read(CTRL_REG1); //Read current settings to be safe
tempSetting |= (1<<1); //Set OST bit
IIC_Write(CTRL_REG1, tempSetting);
}
//Enables the pressure and temp measurement event flags so that we can
//test against them. This is recommended in datasheet during setup.
void enableEventFlags()
{
IIC_Write(PT_DATA_CFG, 0x07); // Enable all three pressure and temp event flags
}
// These are the two I2C functions in this sketch.
byte IIC_Read(byte regAddr)
{
// This function reads one byte over IIC
Wire.beginTransmission(MPL3115A2_ADDRESS);
Wire.write(regAddr); // Address of CTRL_REG1
Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. THIS IS NECESSARY and not supported before Arduino V1.0.1!
Wire.requestFrom(MPL3115A2_ADDRESS, 1); // Request the data...
return Wire.read();
}
void IIC_Write(byte regAddr, byte value)
{
// This function writes one byto over IIC
Wire.beginTransmission(MPL3115A2_ADDRESS);
Wire.write(regAddr);
Wire.write(value);
Wire.endTransmission(true);
}