Modified Barometric Pressure Sensor to make it easier for beginners to understand.

libraries/SPI/examples/BarometricPressureSensor/BarometricPressureSensor.pde

@@ -1,33 +1,37 @@
+
 /*
  SCP1000 Barometric Pressure Sensor Display
 
- Shows the output of a Barometric Pressure Sensor on a
+Shows the output of a Barometric Pressure Sensor on a
- Uses the SPI library. For details on the sensor, see:
+Uses the SPI library. For details on the sensor, see:
- http://www.sparkfun.com/commerce/product_info.php?products_id=8161
+http://www.sparkfun.com/commerce/product_info.php?products_id=8161
- http://www.vti.fi/en/support/obsolete_products/pressure_sensors/
+http://www.vti.fi/en/support/obsolete_products/pressure_sensors/
 
- This sketch adapted from Nathan Seidle's SCP1000 example for PIC:
+This sketch adapted from Nathan Seidle's SCP1000 example for PIC:
- http://www.sparkfun.com/datasheets/Sensors/SCP1000-Testing.zip
+http://www.sparkfun.com/datasheets/Sensors/SCP1000-Testing.zip
 
- Circuit:
+Circuit:
- SCP1000 sensor attached to pins 6, 7, 10 - 13:
+SCP1000 sensor attached to pins 6, 7, 10 - 13:
- DRDY: pin 6
+DRDY: pin 6
- CSB: pin 7
+CSB: pin 7
- MOSI: pin 11    MOSI, MISO, SCK pins are different depending on the 
+MOSI: pin 11
- MISO: pin 12    board type. See your board's documentation for details
+MISO: pin 12
- SCK: pin 13
+SCK: pin 13
 
- created 31 July 2010
+created 31 July 2010
- by Tom Igoe
+modified 14 August 2010
- */
+by Tom Igoe
+*/
 
 // the sensor communicates using SPI, so include the library:
 #include <SPI.h>
 
 //Sensor's memory register addresses:
-const int PRESSURE = 0x1F;      //3 most significant bits of pressure
+const int PRESSURE = 0x1F;       // 3 most significant bits of pressure
-const int PRESSURE_LSB = 0x20;  //16 least significant bits of pressure
+const int PRESSURE_LSB = 0x20;   // 16 least significant bits of pressure
-const int TEMPERATURE = 0x21;   //16 bit temperature reading
+const int TEMPERATURE = 0x21;    // 16 bit temperature reading
+cont byte READ = 0b11111100;     // SCP1000's read command
+const byte WRITE = 0b00000010;   // SCP1000's write command
 
 // pins used for the connection with the sensor
 // the other you need are controlled by the SPI library):
@@ -81,55 +85,34 @@ void loop() {
  }
 }
 
-//Sends a write command to SCP1000
+//Read from or write to register from the SCP1000:
-
+unsigned int readRegister(byte thisRegister, int bytesToRead ) {
-void writeRegister(byte registerName, byte registerValue) {
+ byte inByte = 0;           // incoming byte from the SPI
-  // SCP1000 expects the reguster name in the upper 6 bits
-  // of the byte:
-  registerName <<= 2;
-  // command goes in the lower two bits:
-  registerName |= 0b00000010; //Write command
-
-  // take the chip select low to select the device:
-  digitalWrite(chipSelectPin, LOW); 
-
-  SPI.transfer(registerName); //Send register location
-  SPI.transfer(registerValue); //Send value to record into register
-
-  // take the chip select high to de-select:
-  digitalWrite(chipSelectPin, HIGH); //Select SPI device
-}
-
-
-//Read register from the SCP1000:
-unsigned int readRegister(byte registerName, int numBytes) {
-  byte inByte = 0;           // incoming from  the SPI read
  unsigned int result = 0;   // result to return 
 
-  // SCP1000 expects the reguster name in the upper 6 bits
+ // SCP1000 expects the register name in the upper 6 bits
-  // of the byte:
+ // of the byte. So shift the bits left by two bits:
-  registerName <<= 2;
+ thisRegister = thisRegister << 2;
-  // command goes in the lower two bits:
+ // now combine the address and the command into one byte
-  registerName &= 0b11111100; //Read command
+ dataToSend = thisRegister & READ;
 
  // take the chip select low to select the device:
  digitalWrite(chipSelectPin, LOW); 
  // send the device the register you want to read:
-  int command = SPI.transfer(registerName); 
+ SPI.transfer(dataToSend); 
-  // send a value of 0 to read the forst byte returned:
+ // send a value of 0 to read the first byte returned:
+ result = SPI.transfer(0x00); 
+ // decrement the number of bytes left to read:
+ bytesToRead--;
+ // if you still have another byte to read:
+ if (bytesToRead > 0) {
+   // shift the first byte left, then get the second byte: 
+   result = result << 8;
    inByte = SPI.transfer(0x00); 
-
+   // combine the byte you just got with the previous one:
-  // if there's more than one byte returned, 
+   result = result | inByte;
-  // shift the first byte then get the second byte:
+   // decrement the number of bytes left to read:
-  switch(numBytes) {
+   bytesToRead--;
-  case 1:
-    result = inByte;
-    break;
-  case 2: 
-    result = inByte << 8;
-    inByte = SPI.transfer(0x00); 
-    result = result |inByte;
-    break;
  }
  // take the chip select high to de-select:
  digitalWrite(chipSelectPin, HIGH); 
@@ -138,13 +121,22 @@ unsigned int readRegister(byte registerName, int numBytes) {
 }
 
 
+//Sends a write command to SCP1000
 
+void writeRegister(byte thisRegister, byte thisValue) {
 
+ // SCP1000 expects the register address in the upper 6 bits
+ // of the byte. So shift the bits left by two bits:
+ thisRegister = thisRegister << 2;
+ // now combine the register address and the command into one byte:
+ dataToSend = thisRegister | WRITE;
 
+ // take the chip select low to select the device:
+ digitalWrite(chipSelectPin, LOW); 
 
+ SPI.transfer(dataToSend); //Send register location
+ SPI.transfer(thisValue);  //Send value to record into register
 
-
+ // take the chip select high to de-select:
-
+ digitalWrite(chipSelectPin, HIGH); 
-
+}
-
-