Zoltan Hudak / DS1820

Dallas' DS1820 family temperature sensor. For more details see [https://developer.mbed.org/users/hudakz/code/DS1820/wiki/Homepage]

Dependencies:   OneWire

Dependents:   BLE_nRF24L01 frdm_serialfgmp gather_sensor_data UltiSaverController ... more

Some programs using the DS1820 library:

Import programDS1820_Hello

Simple DS1820 sensor demo showing how to use the DS1820 library [https://developer.mbed.org/users/hudakz/code/DS1820/]

Last commit 20 Jul 2020 by Zoltan Hudak

Import programBLE_nRF24L01

Bluetooth Low Energy (BLE) beacon with nRF24L01(+). Data is received and displayed by Android device (Android app source code is attached).

Last commit 26 Jan 2016 by Zoltan Hudak

Examples of use:

Single DS1820 sensor

/*
 * Single DS1820 sensor GPIO driven
 *
 * Note: Don't forget to connect a 4.7k Ohm resistor 
 *       between the DS1820's data pin and the +3.3V pin
 *
 *           ----------------
 *          |                |   ----------------------->  +3.3V
 *          |   MBED BOARD   |  |
 *          |                |  |   ------
 *          |          +3.3V |--o--| 4.7k |-------
 *          |                |      ------        |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |           GPIO |--------------------o----->  1-wire bus/line
 *          |                |
 *          |                |
 *          |            GND |-------------------------->  GND
 *          |                |
 *           ----------------
 *
 */
 
#include "mbed.h"
#include "DS1820.h"
 
Serial serial(USBTX, USBRX);
 
int main() {
    DS1820  ds1820(D8);    // substitute D8 with actual mbed pin name connected to the DS1820 data pin    
                             
    if(ds1820.begin()) {
        while(1) {
            ds1820.startConversion();     // start temperature conversion
            ThisThread::sleep_for(1000);  // let DS1820 complete the temperature conversion
            serial.printf("temp = %3.1f\r\n", ds1820.read());     // read temperature
        }
    } else
        serial.printf("No DS1820 sensor found!\r\n");
}

Single DS1820 sensor. Data integrity is assured by performing CRC.

/*
 * Single DS1820 sensor GPIO driven + performing CRC
 *
 * Note: Don't forget to connect a 4.7k Ohm resistor 
 *       between the DS1820's data pin and the +3.3V pin
 *
 *           ----------------
 *          |                |   ----------------------->  +3.3V
 *          |   MBED BOARD   |  |
 *          |                |  |   ------
 *          |          +3.3V |--o--| 4.7k |-------
 *          |                |      ------        |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |           GPIO |--------------------o----->  1-wire bus/line
 *          |                |
 *          |                |
 *          |            GND |-------------------------->  GND
 *          |                |
 *           ----------------
 *
 */
 
#include "mbed.h"
#include "DS1820.h"
 
Serial serial(USBTX, USBRX);
 
int main() {
    DS1820  ds1820(D8);    // substitute D8 with actual mbed pin name connected to the DS1820 data pin   
    float   temp = 0;
    int     error = 0; 
                             
    if(ds1820.begin()) {
        while(1) {
            ds1820.startConversion();    // start temperature conversion
            ThisThread::sleep_for(1000); // let DS1820 complete the temperature conversion
            error = ds1820.read(temp);   // read temperature from DS1820 and perform cyclic redundancy check (CRC)
            switch(error) {
            case 0:    // no errors -> 'temp' contains the value of measured temperature
                serial.printf("temp = %3.1f\r\n", temp);
                break;
            case 1:    // no sensor present -> 'temp' is not updated
                serial.printf("no sensor present\n\r");
                break;
            case 2:    // CRC error -> 'temp' is not updated
                serial.printf("CRC error\r\n");
            } 
        }
    } else
        serial.printf("No DS1820 sensor found!\r\n");
}

Several DS1820 sensors connected to the same 1-wire bus.

/*
 * Multiple sensors GPIO driven
 *
 * Note: Don't forget to connect a 4.7k Ohm resistor 
 *       between the 1-wire bus data line and the +3.3V rail
 *
 *           ----------------
 *          |                |   ----------------------->  +3.3V
 *          |   MBED BOARD   |  |
 *          |                |  |   ------
 *          |          +3.3V |--o--| 4.7k |-------
 *          |                |      ------        |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |                |                    |
 *          |           GPIO |--------------------o----->  1-wire bus/line
 *          |                |
 *          |                |
 *          |            GND |-------------------------->  GND
 *          |                |
 *           ----------------
 *
 */

#include "mbed.h"
#include "DS1820.h"

#define     MAX_SENSOSRS   32   // max number of DS1820 sensors to be connected to the 1-wire bus (max 256)

DS1820*     ds1820[MAX_SENSOSRS];
Serial      pc(USBTX, USBRX);
DigitalOut  led(LED1);
OneWire     oneWire(D8);        // substitute D8 with the actual pin name connected to the 1-wire bus
int         sensorsFound = 0;   // counts the actually found DS1820 sensors

int main()
{
    pc.printf("\r\n--Starting--\r\n");
    
    //Enumerate (i.e. detect) DS1820 sensors on the 1-wire bus
    for (sensorsFound = 0; sensorsFound < MAX_SENSOSRS; sensorsFound++) {
        ds1820[sensorsFound] = new DS1820(&oneWire);
        if (!ds1820[sensorsFound]->begin()) {
            delete ds1820[sensorsFound];
            break;
        }
    }

    switch (sensorsFound) {
        case 0:
            pc.printf("No DS1820 sensor found!\r\n");
            return -1;

        case 1:
            pc.printf("One DS1820 sensor found.\r\n");
            break;

        default:
            pc.printf("Found %d DS1820 sensors.\r\n", sensorsFound);
    }

    while (1) {
        pc.printf("----------------\r\n");
        for (int i = 0; i < sensorsFound; i++)
            ds1820[i]->startConversion();        // start temperature conversion from analog to digital
        ThisThread::sleep_for(1000);             // let DS1820 sensors complete the temperature conversion
        for (int i = 0; i < sensorsFound; i++) {
            if (ds1820[i]->isPresent())
                pc.printf("temp[%d] = %3.1f%cC\r\n", i, ds1820[i]->read(), 176); // read temperature
        }
    }
}

Several DS1820 sensors connected to the same 1-wire bus. UART is used to implement the bus

/*
 * Multiple sensors UART driven:
 * 
 *          UART is driving the 1-Wire Bus Master according to Maxim Integrated application note
 *
 *          https://www.maximintegrated.com/en/design/technical-documents/tutorials/2/214.html
 *
 *          In addition to the 4.7k Ohm resistor between the 1-wire data bus/line and the +3.3V pin,
 *          a 470 Ohm resistor shall be tied to the UART's tx and rx pin. UART's rx pin is then used
 *          as 1-wire data bus/line.
 *
 *           ----------------
 *          |                |   ----------------------->  +3.3V
 *          |   MBED BOARD   |  |
 *          |                |  |   ------
 *          |          +3.3V |--o--| 4.7k |-------
 *          |                |      ------        |
 *          |                |      ------        |
 *          |        UART TX |-----|  470 |---    |
 *          |                |      ------    |   |
 *          |                |                |   |
 *          |        UART RX |----------------o---o----->  1-wire bus/line
 *          |                |
 *          |                |
 *          |            GND |-------------------------->  GND
 *          |                |
 *           ----------------
 *
 */
#include "mbed.h"
#include "DS1820.h"

#define MAX_SENSOSRS    32      // max number of DS1820 sensors to be connected to the 1-wire bus (max 256)
DS1820*     ds1820[MAX_SENSOSRS];
DigitalOut  led(LED1);
OneWire     oneWire(p9, p10);       // LPC1768 (UART Tx pin, UART Rx pin)
//OneWire     oneWire(PA_0, PA_1);    // NUCLE0-F446RE (UART Tx pin, UART Rx pin)
int         sensorsFound = 0;       // counts the actually found DS1820 sensors

/**
 * @brief
 * @note
 * @param
 * @retval
 */
int main()
{
    printf("\r\n--Starting--\r\n");

    //Enumerate (i.e. detect) DS1820 sensors on the 1-wire bus
    for (sensorsFound = 0; sensorsFound < MAX_SENSOSRS; sensorsFound++) {
        ds1820[sensorsFound] = new DS1820(&oneWire);
        if (!ds1820[sensorsFound]->begin()) {
            delete ds1820[sensorsFound];
            break;
        }
    }

    switch (sensorsFound) {
        case 0:
            printf("No DS1820 sensor found!\r\n");
            return -1;

        case 1:
            printf("One DS1820 sensor found.\r\n");
            break;

        default:
            printf("Found %d DS1820 sensors.\r\n", sensorsFound);
    }

    while (1) {
        led = !led;

        printf("----------------\r\n");
        for (int i = 0; i < sensorsFound; i++)
            ds1820[i]->startConversion();   // start temperature conversion from analog to digital
        #if (MBED_MAJOR_VERSION > 5)
            ThisThread::sleep_for(1s);
        #else
            wait(1);
        #endif


        for (int i = 0; i < sensorsFound; i++) {
            if (ds1820[i]->isPresent())
                printf("temp[%d] = %3.1f%cC\r\n", i, ds1820[i]->read(), 176);   // read temperature
        }
    }
}

DS1820.cpp@4:adf4e7972d73, 2015-03-20 (annotated)

Committer:
hudakz
Date:
Fri Mar 20 10:07:22 2015 +0000
Revision:
4:adf4e7972d73
Parent:
3:a250babd0a9f
Child:
6:518950e436be
Function to set temperature-to-digital conversion resolution added.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
hudakz 3:a250babd0a9f 1 /*
hudakz 3:a250babd0a9f 2 * Dallas' DS1820 family temperature sensor.
hudakz 3:a250babd0a9f 3 * This library depends on the OneWire library (Dallas' 1-Wire bus protocol implementation)
hudakz 3:a250babd0a9f 4 * which is available at <http://developer.mbed.org/users/hudakz/code/OneWire/>
hudakz 3:a250babd0a9f 5 *
hudakz 3:a250babd0a9f 6 * Example of use:
hudakz 3:a250babd0a9f 7 *
hudakz 3:a250babd0a9f 8 * #include "DS1820.h"
hudakz 3:a250babd0a9f 9 *
hudakz 3:a250babd0a9f 10 * int main() {
hudakz 3:a250babd0a9f 11 * DS1820 ds1820(PA_9);
hudakz 3:a250babd0a9f 12 *
hudakz 3:a250babd0a9f 13 * if(ds1820.begin()) {
hudakz 3:a250babd0a9f 14 * ds1820.startConversion();
hudakz 3:a250babd0a9f 15 * wait(1.0);
hudakz 3:a250babd0a9f 16 * while(1) {
hudakz 3:a250babd0a9f 17 * serial.printf("temp = %3.1f\r\n", ds1820.read());
hudakz 3:a250babd0a9f 18 * ds1820.startConversion();
hudakz 3:a250babd0a9f 19 * wait(1.0);
hudakz 3:a250babd0a9f 20 * }
hudakz 3:a250babd0a9f 21 * } else
hudakz 3:a250babd0a9f 22 * serial.printf("No DS1820 sensor found!\r\n");
hudakz 3:a250babd0a9f 23 * }
hudakz 3:a250babd0a9f 24 */
hudakz 3:a250babd0a9f 25
hudakz 0:433af64321d5 26 #include "DS1820.h"
hudakz 0:433af64321d5 27
hudakz 1:e4689408d617 28 #define DEBUG 0
hudakz 0:433af64321d5 29
hudakz 0:433af64321d5 30 #if DEBUG
hudakz 0:433af64321d5 31 extern Serial serial;
hudakz 0:433af64321d5 32 #endif
hudakz 0:433af64321d5 33
hudakz 0:433af64321d5 34 /**
hudakz 0:433af64321d5 35 * @brief Constructs a generic DS1820 sensor
hudakz 0:433af64321d5 36 * @note begin() must be called to detect and initialize the actual model
hudakz 3:a250babd0a9f 37 * @param pin: Name of data pin
hudakz 0:433af64321d5 38 * @retval
hudakz 0:433af64321d5 39 */
hudakz 0:433af64321d5 40 DS1820::DS1820(PinName pin) :
hudakz 0:433af64321d5 41 oneWire(pin) {
hudakz 0:433af64321d5 42 present = 0;
hudakz 0:433af64321d5 43 type_s = 0;
hudakz 0:433af64321d5 44 }
hudakz 0:433af64321d5 45
hudakz 0:433af64321d5 46 /**
hudakz 0:433af64321d5 47 * @brief Constructs a specific model
hudakz 0:433af64321d5 48 * @note No need to call begin() to detect and initialize the model
hudakz 3:a250babd0a9f 49 * @param model: One character model name: 'S', 's', 'B' or 'b'
hudakz 3:a250babd0a9f 50 * pin: Name of data pin
hudakz 0:433af64321d5 51 * @retval
hudakz 0:433af64321d5 52 */
hudakz 0:433af64321d5 53 DS1820::DS1820(char model, PinName pin) :
hudakz 0:433af64321d5 54 oneWire(pin) {
hudakz 0:433af64321d5 55 if((model == 'S') or (model == 's')) {
hudakz 0:433af64321d5 56 present = 1;
hudakz 0:433af64321d5 57 type_s = 1;
hudakz 0:433af64321d5 58 }
hudakz 0:433af64321d5 59 else if((model == 'B') or (model == 'b')) {
hudakz 0:433af64321d5 60 present = 1;
hudakz 0:433af64321d5 61 type_s = 0;
hudakz 0:433af64321d5 62 }
hudakz 0:433af64321d5 63 else
hudakz 0:433af64321d5 64 present = 0;
hudakz 0:433af64321d5 65 }
hudakz 0:433af64321d5 66
hudakz 0:433af64321d5 67 /**
hudakz 0:433af64321d5 68 * @brief Detects and initializes the actual DS1820 model
hudakz 0:433af64321d5 69 * @note
hudakz 0:433af64321d5 70 * @param
hudakz 0:433af64321d5 71 * @retval true: if a DS1820 family sensor was detected and initialized
hudakz 0:433af64321d5 72 false: otherwise
hudakz 0:433af64321d5 73 */
hudakz 0:433af64321d5 74 bool DS1820::begin(void) {
hudakz 0:433af64321d5 75 oneWire.reset_search();
hudakz 0:433af64321d5 76 wait_ms(250);
hudakz 0:433af64321d5 77 if(!oneWire.search(addr)) {
hudakz 0:433af64321d5 78 #if DEBUG
hudakz 0:433af64321d5 79 serial.printf("No addresses.\r\n");
hudakz 0:433af64321d5 80 #endif
hudakz 0:433af64321d5 81 oneWire.reset_search();
hudakz 0:433af64321d5 82 wait_ms(250);
hudakz 0:433af64321d5 83 return false;
hudakz 0:433af64321d5 84 }
hudakz 0:433af64321d5 85
hudakz 0:433af64321d5 86 #if DEBUG
hudakz 0:433af64321d5 87 serial.printf("ROM =");
hudakz 0:433af64321d5 88 for(uint8_t i = 0; i < 8; i++) {
hudakz 0:433af64321d5 89 serial.printf(" %x", addr[i]);
hudakz 0:433af64321d5 90 }
hudakz 0:433af64321d5 91 serial.printf("\r\n");
hudakz 0:433af64321d5 92 #endif
hudakz 0:433af64321d5 93
hudakz 0:433af64321d5 94 if(OneWire::crc8(addr, 7) == addr[7]) {
hudakz 0:433af64321d5 95 present = 1;
hudakz 0:433af64321d5 96
hudakz 0:433af64321d5 97 // the first ROM byte indicates which chip
hudakz 0:433af64321d5 98 switch(addr[0]) {
hudakz 0:433af64321d5 99 case 0x10:
hudakz 0:433af64321d5 100 type_s = 1;
hudakz 0:433af64321d5 101 #if DEBUG
hudakz 0:433af64321d5 102 serial.printf("DS18S20 or old DS1820\r\n");
hudakz 0:433af64321d5 103 #endif
hudakz 0:433af64321d5 104 break;
hudakz 0:433af64321d5 105
hudakz 0:433af64321d5 106 case 0x28:
hudakz 0:433af64321d5 107 type_s = 0;
hudakz 0:433af64321d5 108 #if DEBUG
hudakz 0:433af64321d5 109 serial.printf("DS18B20\r\n");
hudakz 0:433af64321d5 110 #endif
hudakz 0:433af64321d5 111 break;
hudakz 0:433af64321d5 112
hudakz 0:433af64321d5 113 case 0x22:
hudakz 0:433af64321d5 114 type_s = 0;
hudakz 0:433af64321d5 115 #if DEBUG
hudakz 0:433af64321d5 116 serial.printf("DS1822\r\n");
hudakz 0:433af64321d5 117 #endif
hudakz 0:433af64321d5 118 break;
hudakz 0:433af64321d5 119
hudakz 0:433af64321d5 120 default:
hudakz 0:433af64321d5 121 present = 0;
hudakz 0:433af64321d5 122 #if DEBUG
hudakz 0:433af64321d5 123 serial.printf("Device doesn't belong to the DS1820 family\r\n");
hudakz 2:b7ad1da7331a 124 #endif
hudakz 0:433af64321d5 125 return false;
hudakz 0:433af64321d5 126 }
hudakz 0:433af64321d5 127 return true;
hudakz 0:433af64321d5 128 }
hudakz 2:b7ad1da7331a 129 else {
hudakz 0:433af64321d5 130 #if DEBUG
hudakz 0:433af64321d5 131 serial.printf("Invalid CRC!\r\n");
hudakz 2:b7ad1da7331a 132 #endif
hudakz 0:433af64321d5 133 return false;
hudakz 0:433af64321d5 134 }
hudakz 0:433af64321d5 135 }
hudakz 0:433af64321d5 136
hudakz 0:433af64321d5 137 /**
hudakz 4:adf4e7972d73 138 * @brief Sets temperature-to-digital conversion resolution
hudakz 4:adf4e7972d73 139 * @note The configuration register allows the user to set the resolution
hudakz 4:adf4e7972d73 140 * of the temperature-to-digital conversion to 9, 10, 11, or 12 bits
hudakz 4:adf4e7972d73 141 * Defaults to 12bit resolution for DS18B20.
hudakz 4:adf4e7972d73 142 * DS18S20 allows only 9bit resolution.
hudakz 4:adf4e7972d73 143 * @param res: Resolution of the temperature-to-digital conversion in bits
hudakz 4:adf4e7972d73 144 * @retval
hudakz 4:adf4e7972d73 145 */
hudakz 4:adf4e7972d73 146 void DS1820::setResolution(uint8_t res) {
hudakz 4:adf4e7972d73 147 // keep resolution within limits
hudakz 4:adf4e7972d73 148 if(res > 12)
hudakz 4:adf4e7972d73 149 res = 12;
hudakz 4:adf4e7972d73 150 if(res < 9)
hudakz 4:adf4e7972d73 151 res = 9;
hudakz 4:adf4e7972d73 152 if(type_s)
hudakz 4:adf4e7972d73 153 res = 9;
hudakz 4:adf4e7972d73 154
hudakz 4:adf4e7972d73 155 oneWire.reset();
hudakz 4:adf4e7972d73 156 oneWire.skip();
hudakz 4:adf4e7972d73 157 oneWire.write(0xBE); // to read Scratchpad
hudakz 4:adf4e7972d73 158 for(uint8_t i = 0; i < 9; i++) // read Scratchpad bytes
hudakz 4:adf4e7972d73 159 data[i] = oneWire.read();
hudakz 4:adf4e7972d73 160
hudakz 4:adf4e7972d73 161 data[4] |= (res - 9) << 5; // update configuration byte (set resolution)
hudakz 4:adf4e7972d73 162 oneWire.reset();
hudakz 4:adf4e7972d73 163 oneWire.skip();
hudakz 4:adf4e7972d73 164 oneWire.write(0x4E); // to write into Scratchpad
hudakz 4:adf4e7972d73 165 for(uint8_t i = 2; i < 5; i++) // write three bytes (2nd, 3rd, 4th) into Scratchpad
hudakz 4:adf4e7972d73 166 oneWire.write(data[i]);
hudakz 4:adf4e7972d73 167 }
hudakz 4:adf4e7972d73 168
hudakz 4:adf4e7972d73 169
hudakz 4:adf4e7972d73 170 /**
hudakz 0:433af64321d5 171 * @brief Starts temperature conversion
hudakz 0:433af64321d5 172 * @note The time to complete the converion depends on the selected resolusion
hudakz 0:433af64321d5 173 * @param
hudakz 0:433af64321d5 174 * @retval
hudakz 0:433af64321d5 175 */
hudakz 0:433af64321d5 176 void DS1820::startConversion(void) {
hudakz 0:433af64321d5 177 if(present) {
hudakz 0:433af64321d5 178 oneWire.reset();
hudakz 0:433af64321d5 179 oneWire.skip();
hudakz 3:a250babd0a9f 180 oneWire.write(0x44); //start temperature conversion
hudakz 0:433af64321d5 181 }
hudakz 0:433af64321d5 182 }
hudakz 0:433af64321d5 183
hudakz 0:433af64321d5 184 /**
hudakz 0:433af64321d5 185 * @brief Reads temperature from the chip's scratchpad
hudakz 0:433af64321d5 186 * @note
hudakz 0:433af64321d5 187 * @param
hudakz 0:433af64321d5 188 * @retval Floating point temperature value
hudakz 0:433af64321d5 189 */
hudakz 0:433af64321d5 190 float DS1820::read(void) {
hudakz 0:433af64321d5 191 if(present) {
hudakz 0:433af64321d5 192 oneWire.reset();
hudakz 0:433af64321d5 193 oneWire.skip();
hudakz 0:433af64321d5 194 oneWire.write(0xBE); // to read Scratchpad
hudakz 0:433af64321d5 195 for(uint8_t i = 0; i < 9; i++)
hudakz 0:433af64321d5 196 data[i] = oneWire.read();
hudakz 0:433af64321d5 197
hudakz 4:adf4e7972d73 198 // Convert the raw bytes to a 16bit unsigned value
hudakz 0:433af64321d5 199 uint16_t* p_word = reinterpret_cast < uint16_t * > (&data[0]);
hudakz 0:433af64321d5 200
hudakz 0:433af64321d5 201 #if DEBUG
hudakz 0:433af64321d5 202 serial.printf("raw = %#x\r\n", *p_word);
hudakz 0:433af64321d5 203 #endif
hudakz 0:433af64321d5 204
hudakz 0:433af64321d5 205 if(type_s) {
hudakz 4:adf4e7972d73 206 *p_word = *p_word << 3; // 9 bit resolution, max conversion time = 750ms
hudakz 0:433af64321d5 207 if(data[7] == 0x10) {
hudakz 0:433af64321d5 208
hudakz 0:433af64321d5 209 // "count remain" gives full 12 bit resolution
hudakz 0:433af64321d5 210 *p_word = (*p_word & 0xFFF0) + 12 - data[6];
hudakz 0:433af64321d5 211 }
hudakz 0:433af64321d5 212
hudakz 4:adf4e7972d73 213 // Convert the raw bytes to a 16bit signed fixed point value :
hudakz 4:adf4e7972d73 214 // 1 sign bit, 7 integer bits, 8 fractional bits (two’s compliment
hudakz 4:adf4e7972d73 215 // and the LSB of the 16bit binary number represents 1/256th of a unit).
hudakz 0:433af64321d5 216 *p_word = *p_word << 4;
hudakz 4:adf4e7972d73 217 // Convert to floating point value
hudakz 0:433af64321d5 218 return(toFloat(*p_word));
hudakz 0:433af64321d5 219 }
hudakz 0:433af64321d5 220 else {
hudakz 4:adf4e7972d73 221 uint8_t cfg = (data[4] & 0x60); // default 12bit resolution, max conversion time = 750ms
hudakz 4:adf4e7972d73 222
hudakz 4:adf4e7972d73 223 // at lower resolution, the low bits are undefined, so let's clear them
hudakz 0:433af64321d5 224 if(cfg == 0x00)
hudakz 4:adf4e7972d73 225 *p_word = *p_word &~7; // 9bit resolution, max conversion time = 93.75ms
hudakz 0:433af64321d5 226 else
hudakz 0:433af64321d5 227 if(cfg == 0x20)
hudakz 4:adf4e7972d73 228 *p_word = *p_word &~3; // 10bit resolution, max conversion time = 187.5ms
hudakz 0:433af64321d5 229 else
hudakz 0:433af64321d5 230 if(cfg == 0x40)
hudakz 4:adf4e7972d73 231 *p_word = *p_word &~1; // 11bit resolution, max conversion time = 375ms
hudakz 4:adf4e7972d73 232
hudakz 4:adf4e7972d73 233 // Convert the raw bytes to a 16bit signed fixed point value :
hudakz 4:adf4e7972d73 234 // 1 sign bit, 7 integer bits, 8 fractional bits (two’s compliment
hudakz 4:adf4e7972d73 235 // and the LSB of the 16bit binary number represents 1/256th of a unit).
hudakz 4:adf4e7972d73 236 *p_word = *p_word << 4;
hudakz 4:adf4e7972d73 237 // Convert to floating point value
hudakz 0:433af64321d5 238 return(toFloat(*p_word));
hudakz 0:433af64321d5 239 }
hudakz 0:433af64321d5 240 }
hudakz 0:433af64321d5 241 else
hudakz 0:433af64321d5 242 return 0;
hudakz 0:433af64321d5 243 }
hudakz 0:433af64321d5 244
hudakz 0:433af64321d5 245 /**
hudakz 3:a250babd0a9f 246 * @brief Converts a 16bit signed fixed point value to floating point value
hudakz 0:433af64321d5 247 * @note The 16bit unsigned integer represnts actually
hudakz 0:433af64321d5 248 * a 16bit signed fixed point value:
hudakz 4:adf4e7972d73 249 * 1 sign bit, 7 integer bits, 8 fractional bits (two’s compliment
hudakz 4:adf4e7972d73 250 * and the LSB of the 16bit binary number represents 1/256th of a unit).
hudakz 0:433af64321d5 251 * @param 16bit unsigned integer
hudakz 4:adf4e7972d73 252 * @retval Floating point value
hudakz 0:433af64321d5 253 */
hudakz 0:433af64321d5 254 float DS1820::toFloat(uint16_t word) {
hudakz 0:433af64321d5 255 if(word & 0x8000)
hudakz 0:433af64321d5 256 return (-float(uint16_t(~word + 1)) / 256.0f);
hudakz 0:433af64321d5 257 else
hudakz 0:433af64321d5 258 return (float(word) / 256.0f);
hudakz 0:433af64321d5 259 }
hudakz 0:433af64321d5 260