main.cpp

00001 #include "mbed.h"
00002 
00003 /*
00004 ***************************************************************************
00005 MCP9800_Test. 9-12 bit temperature sensor and thermostat.
00006 2.7-5.5 V. 4.7kOhm pull-up resistors at SDA and SCLK.
00007 
00008 This program sets 12 bit ambient temperature readings resolution.
00009 
00010 Pointer bits:
00011 00: temperature register. 01: configuration register.
00012 10: temperature hysteresis register. 11: temperature limit-set register.
00013 Author: Lluis Nadal. August 2011.
00014 ***************************************************************************
00015 */
00016 
00017 I2C i2c(p9, p10); // SDA, SCL
00018 Serial pc(USBTX, USBRX);
00019 
00020 const int addr_R = 0x91; // Address to read
00021 const int addr_W = 0x90; // Address to write
00022 //const int addr_R = 0x9B ; // Address to read
00023 //const int addr_W = 0x9A; // Address to write
00024 
00025 char data[3];
00026 char TL[2];
00027 char TLR[2];
00028 char TH[2];
00029 char CR[1];
00030 int t;
00031 float temp;
00032 
00033 
00034 void read_temp() {
00035 
00036     int sign;
00037     i2c.start();
00038     i2c.write(addr_W);//Address to write pointer
00039     i2c.write(0x00);// Write pointer to ambient temperature register
00040     i2c.read(addr_R, data, 2);
00041     i2c.stop();
00042 
00043     //pc.printf("Temperature register: (%d, %d)\r\n",data[0], data[1]);
00044     sign = data[0]>>7;
00045     //pc.printf("Sign: %d \r\n",sign);
00046 
00047     if (sign == 1) { // If number is negative
00048         data[0] = ~data[0]; // Inverts (compliments)the bits
00049         data[1] = ~data[1]; // Inverts (compliments)the bits
00050         t = data[0];
00051         t = -((t<<4) | (data[1]>>4)+1);// Packs and adds one to convert to negative integer
00052         temp = t/16.0;
00053     }
00054 
00055     else {
00056         t = data[0];
00057         t = ((t<<4) | (data[1]>>4));
00058         temp = t/16.0;
00059     }
00060     pc.printf("Temperature: %.4f C\r\n",temp);
00061     pc.printf("\r\n");
00062 }
00063 
00064 
00065 void read_TL() {      // Read temperature limit register
00066 
00067     i2c.start();
00068     i2c.write(addr_W);//Address to write pointer
00069     i2c.write(0x03);// Write pointer to TL register
00070     i2c.read(addr_R, TLR, 2);
00071     i2c.stop();
00072     pc.printf("Temperature limit register: (%d, %d)\r\n",TLR[0], TLR[1]);
00073     pc.printf("\r\n");
00074 }
00075 
00076 void read_TH() {     // Read hysteresis register
00077 
00078     i2c.start();
00079     i2c.write(addr_W);//Address to write pointer
00080     i2c.write(0x02);// Write pointer to TH register
00081     i2c.read(addr_R, TH, 2);
00082     i2c.stop();
00083 
00084     pc.printf("Temperature hysteresis register: (%d, %d)\r\n",TH[0], TH[1]);
00085     pc.printf("\r\n");
00086 }
00087 
00088 
00089 void read_CR() {        // Read configuration register
00090 
00091     i2c.start();
00092     i2c.write(addr_W);//Address to write pointer
00093     i2c.write(0x01);// Write pointer to configuration register
00094     i2c.read(addr_R, CR, 1);
00095     i2c.stop();
00096 
00097     pc.printf("Configuration register: (%d)\r\n",CR[0]);
00098     pc.printf("\r\n");
00099 }
00100 
00101 // Set temperature limit (9-bit)
00102 void set_TL(float n) {  // -25.4375, 25.4375, 125, -55...
00103     char msb;
00104     char lsb;
00105     if (n < 0) {
00106         t = (int)(-n*16.0-1);
00107         pc.printf("t = %d\r\n", t);
00108         t = t<<4;
00109         lsb = t & 0xFF;
00110         msb = t>>8;
00111         lsb = ~lsb; //Inverts (compliments)the bits
00112         msb = ~msb; //Inverts (compliments)the bits
00113 //pc.printf("(%d, %d)\r\b", msb, lsb);
00114     } else {
00115         t = (int)(n*16.0);
00116         t = t<<4;
00117         lsb = t & 0xFF;
00118         msb = t>>8;
00119 //pc.printf("(%d, %d)\r\b", msb, lsb);
00120     }
00121     i2c.start();
00122     i2c.write(addr_W);//Address to write pointer
00123     i2c.write(0x03);// Write pointer to temperature-limit register
00124     i2c.write(msb);// Write data
00125     i2c.write(lsb);// Write data
00126     i2c.stop();
00127 }
00128 
00129 // Set hysteresis register (9-bit)
00130 void set_TH(float n) {  // -25.4375, 25.4375, 125, -55...
00131     char msb;
00132     char lsb;
00133     if (n < 0) {
00134         t = (int)(-n*16.0-1);
00135         pc.printf("t = %d\r\n", t);
00136         t = t<<4;
00137         lsb = t & 0xFF;
00138         msb = t>>8;
00139         lsb = ~lsb; //Inverts (compliments)the bits
00140         msb = ~msb; //Inverts (compliments)the bits
00141 //pc.printf("(%d, %d)\r\b", msb, lsb);
00142     } else {
00143         t = (int)(n*16.0);
00144         t = t<<4;
00145         lsb = t & 0xFF;
00146         msb = t>>8;
00147 //pc.printf("(%d, %d)\r\b", msb, lsb);
00148     }
00149     i2c.start();
00150     i2c.write(addr_W);//Address to write pointer
00151     i2c.write(0x02);// Write pointer to hysteresis register
00152     i2c.write(msb);// Write data
00153     i2c.write(lsb);// Write data
00154     i2c.stop();
00155 }
00156 
00157 
00158 
00159 
00160 
00161 int main() {
00162 
00163     i2c.frequency(200000); // Max 400000 Hz
00164 
00165     pc.printf("Initial readings: \r\n");
00166     pc.printf("\r\n");
00167     read_TL(); // Read temperature limit register
00168     read_TH(); // Read hysteresis register
00169     read_CR(); // Read configuration register
00170 
00171     // Set 12 bit resolution
00172     i2c.start();
00173     i2c.write(addr_W);//Address to write pointer
00174     i2c.write(0x01);// Write pointer to configuration register
00175     i2c.write(0x60);// Write data
00176     i2c.stop();
00177 
00178     // Set temperature limit (9-bit)
00179     set_TL(25.4375);   // -25.4375, 25.4375, 125, -55...
00180 // If ambient temperature > temperature limit then alert pin is low (with a pull-up resistor).
00181 
00182 
00183     // Set hysteresis register (9-bit)
00184     set_TH(24.4375);   // -25.4375, 25.4375, 125, -55...
00185 
00186     wait(1);
00187 
00188     pc.printf("\r\n");
00189     pc.printf("Readings after changes: \r\n");
00190     pc.printf("\r\n");
00191     read_TL();       // Read temperature limit register
00192     read_TH();       // Read hysteresis register
00193     read_CR();       // Read configuration register
00194     read_temp();     // Read ambient temperature
00195     pc.printf("\r\n");
00196 
00197 }