Diff: main.cpp

Revision:

0:bc0f96339b73

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Nov 01 01:47:38 2017 +0000
@@ -0,0 +1,105 @@
+#include "mbed.h"
+#include "USBSerial.h"
+#include "max32625pico.h"
+
+USBSerial pc;
+
+int readTemp(I2C &i2cbus);
+void configTemp(I2C &i2cbus);
+
+#define WRITE_ADDRESS   0x90
+#define READ_ADDRESS    0x91
+#define TEMP_REG        0x00
+#define CONFIG_REG      0x01
+
+int main()
+{
+    //initialize the MAX32625PICO board for +3.3V logic levels
+    MAX32625PICO pico(MAX32625PICO::IOH_3V3, MAX32625PICO::VIO_IOH, MAX32625PICO::VIO_IOH);
+    
+    //initialize RGB LED channels and turn them off
+    DigitalOut rLED(LED1, LED_OFF);
+    DigitalOut gLED(LED2, LED_OFF);
+    DigitalOut bLED(LED3, LED_OFF);
+    
+    //initialize the I2C master interface
+    I2C i2c(P1_6, P1_7);    //SDA, SCL
+    
+    //delcare variables to store the raw temperature readings and the converted Celsius temperature
+    int temperature_raw;
+    float temperature_C;
+    
+    //write the configuration register
+    configTemp(i2c);
+    
+    //the while loop will read the temperature reading, convert to Celsius, and then
+    //print the result to a serial terminal. It will then toggle each on-board LED
+    //for 11ms for a total of 33ms. A new temperature value is available every 12.5ms.
+    while (true) {
+        //the readTemp() function returns a raw 16-bit temperature reading
+        //if successful and a zero if unsuccessful
+        temperature_raw = readTemp(i2c);
+        
+        //print temperature only if valid data is received. Readings of exactly 0.00 degrees
+        //will be thrown out but really what are the chances?
+        if(temperature_raw != 0)
+        {
+            temperature_C = temperature_raw/256.0;
+            
+            //print a floating point value with 4 decimal places
+            pc.printf("\r\n%.4f C",temperature_C);
+        }
+        else {
+            pc.printf("\r\nTemp Read Error");
+        }
+        
+        //toggle LEDs one at a time for a total of 33ms
+        bLED = LED_OFF;
+        rLED = LED_ON;
+        wait(0.11);
+        rLED = LED_OFF;
+        gLED = LED_ON;
+        wait(0.11);
+        gLED = LED_OFF;
+        bLED = LED_ON;
+        wait(0.11);
+    }
+}
+
+void configTemp(I2C &i2cbus)
+{
+    //creates an array to store the values to be written to the configuration register
+    //values chosen will program the MAX31875 for 8 conversions/second and 12-bit resolution
+    char data[3] = {CONFIG_REG, 0x00, 0x66};
+    
+    //this built-in I2C write function from mbed sends the configuration data to the MAX31875
+    i2cbus.write(WRITE_ADDRESS, data, 3, false);
+}
+
+int readTemp(I2C &i2cbus)
+{
+    int temp_raw = 0;
+    char data[2] = {TEMP_REG, 0};
+    
+    //the first I2C command sets the MAX31875 to point to the temperature register
+    //it returns a zero on success or non-zero if unsuccessful
+    int rtn_val = i2cbus.write(WRITE_ADDRESS, data, 1, true);
+    
+    //proceeds to read temperature only if previous command was successful
+    if(rtn_val == 0)
+    {
+        //this I2C command reads the temperature and stores it in the 'data' array.
+        //it returns a zero on success or non-zero if unsuccessful
+        rtn_val = i2cbus.read(READ_ADDRESS, data, 2, false);
+        
+        //proceeds to format raw temperature data only if previous command was successful
+        if(rtn_val == 0)
+        {
+            //combine both 8-bit register readings into one 16-bit variable
+            temp_raw = ((data[0] << 8) | data[1]);
+        }
+    }
+    //returns the 16-bit raw temperature reading
+    return temp_raw;
+}
+    
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