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/*
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 SCP1000 Barometric Pressure Sensor Display
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 Shows the output of a Barometric Pressure Sensor on a
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 Uses the SPI library. For details on the sensor, see:
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 http://www.sparkfun.com/commerce/product_info.php?products_id=8161
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 http://www.vti.fi/en/support/obsolete_products/pressure_sensors/
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 This sketch adapted from Nathan Seidle's SCP1000 example for PIC:
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 http://www.sparkfun.com/datasheets/Sensors/SCP1000-Testing.zip
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 Circuit:
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 SCP1000 sensor attached to pins 6, 7, 10 - 13:
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 DRDY: pin 6
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 CSB: pin 7
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 MOSI: pin 11
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 MISO: pin 12
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 SCK: pin 13
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 created 31 July 2010
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 modified 14 August 2010
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 by Tom Igoe
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 */
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// the sensor communicates using SPI, so include the library:
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#include <SPI.h>
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//Sensor's memory register addresses:
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const int PRESSURE = 0x1F;      //3 most significant bits of pressure
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const int PRESSURE_LSB = 0x20;  //16 least significant bits of pressure
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const int TEMPERATURE = 0x21;   //16 bit temperature reading
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const byte READ = 0b11111100;     // SCP1000's read command
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const byte WRITE = 0b00000010;   // SCP1000's write command
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// pins used for the connection with the sensor
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// the other you need are controlled by the SPI library):
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const int dataReadyPin = 6;
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const int chipSelectPin = 7;
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void setup() {
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  Serial.begin(9600);
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  // start the SPI library:
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  SPI.begin();
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  // initalize the  data ready and chip select pins:
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  pinMode(dataReadyPin, INPUT);
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  pinMode(chipSelectPin, OUTPUT);
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  //Configure SCP1000 for low noise configuration:
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  writeRegister(0x02, 0x2D);
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  writeRegister(0x01, 0x03);
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  writeRegister(0x03, 0x02);
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  // give the sensor time to set up:
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  delay(100);
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}
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void loop() {
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  //Select High Resolution Mode
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  writeRegister(0x03, 0x0A);
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  // don't do anything until the data ready pin is high:
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  if (digitalRead(dataReadyPin) == HIGH) {
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    //Read the temperature data
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    int tempData = readRegister(0x21, 2);
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    // convert the temperature to celsius and display it:
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    float realTemp = (float)tempData / 20.0;
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    Serial.print("Temp[C]=");
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    Serial.print(realTemp);
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    //Read the pressure data highest 3 bits:
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    byte  pressure_data_high = readRegister(0x1F, 1);
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    pressure_data_high &= 0b00000111; //you only needs bits 2 to 0
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    //Read the pressure data lower 16 bits:
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    unsigned int pressure_data_low = readRegister(0x20, 2);
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    //combine the two parts into one 19-bit number:
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    long pressure = ((pressure_data_high << 16) | pressure_data_low)/4;
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    // display the temperature:
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    Serial.println("\tPressure [Pa]=" + String(pressure));
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  }
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}
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//Read from or write to register from the SCP1000:
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unsigned int readRegister(byte thisRegister, int bytesToRead ) {
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  byte inByte = 0;           // incoming byte from the SPI
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  unsigned int result = 0;   // result to return
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  Serial.print(thisRegister, BIN);
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  Serial.print("\t");
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  // SCP1000 expects the register name in the upper 6 bits
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  // of the byte. So shift the bits left by two bits:
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  thisRegister = thisRegister << 2;
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  // now combine the address and the command into one byte
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  byte dataToSend = thisRegister & READ;
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  Serial.println(thisRegister, BIN);
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  // take the chip select low to select the device:
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  digitalWrite(chipSelectPin, LOW);
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  // send the device the register you want to read:
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  SPI.transfer(dataToSend);
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  // send a value of 0 to read the first byte returned:
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  result = SPI.transfer(0x00);
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  // decrement the number of bytes left to read:
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  bytesToRead--;
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  // if you still have another byte to read:
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  if (bytesToRead > 0) {
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    // shift the first byte left, then get the second byte:
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    result = result << 8;
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    inByte = SPI.transfer(0x00);
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    // combine the byte you just got with the previous one:
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    result = result | inByte;
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    // decrement the number of bytes left to read:
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    bytesToRead--;
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  }
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  // take the chip select high to de-select:
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  digitalWrite(chipSelectPin, HIGH);
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  // return the result:
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  return(result);
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}
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//Sends a write command to SCP1000
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void writeRegister(byte thisRegister, byte thisValue) {
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  // SCP1000 expects the register address in the upper 6 bits
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  // of the byte. So shift the bits left by two bits:
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  thisRegister = thisRegister << 2;
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  // now combine the register address and the command into one byte:
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  byte dataToSend = thisRegister | WRITE;
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  // take the chip select low to select the device:
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  digitalWrite(chipSelectPin, LOW);
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  SPI.transfer(dataToSend); //Send register location
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  SPI.transfer(thisValue);  //Send value to record into register
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  // take the chip select high to de-select:
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  digitalWrite(chipSelectPin, HIGH);
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}
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