Read temperature from DS18B20+

include/ds18b20.h

@@ -0,0 +1,53 @@
+/*
+ds18b20 lib 0x02
+
+copyright (c) Davide Gironi, 2012
+
+Released under GPLv3.
+Please refer to LICENSE file for licensing information.
+
+References:
+  + Using DS18B20 digital temperature sensor on AVR microcontrollers
+    by Gerard Marull Paretas, 2007
+    http://teslabs.com/openplayer/docs/docs/other/ds18b20_pre1.pdf
+*/
+
+
+#ifndef DS18B20_H_
+#define DS18B20_H_
+
+#include <avr/io.h>
+
+//setup connection
+
+#define DS18B20_PORT PORTD
+#define DS18B20_DDR DDRD
+#define DS18B20_PIN PIND
+#define DS18B20_DQ PD7
+
+//commands
+#define DS18B20_CMD_CONVERTTEMP 0x44
+#define DS18B20_CMD_RSCRATCHPAD 0xbe
+#define DS18B20_CMD_WSCRATCHPAD 0x4e
+#define DS18B20_CMD_CPYSCRATCHPAD 0x48
+#define DS18B20_CMD_RECEEPROM 0xb8
+#define DS18B20_CMD_RPWRSUPPLY 0xb4
+#define DS18B20_CMD_SEARCHROM 0xf0
+#define DS18B20_CMD_READROM 0x33
+#define DS18B20_CMD_MATCHROM 0x55
+#define DS18B20_CMD_SKIPROM 0xcc
+#define DS18B20_CMD_ALARMSEARCH 0xec
+
+//stop any interrupt on read
+#define DS18B20_STOPINTERRUPTONREAD 1
+
+//functions
+uint8_t ds18b20_reset(void);
+void ds18b20_writebit(uint8_t bit);
+uint8_t ds18b20_readbit(void);
+void ds18b20_writebyte(uint8_t byte);
+uint8_t ds18b20_readbyte(void);
+
+extern double ds18b20_gettemp(void);
+
+#endif

main.c

@@ -1,6 +1,7 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
+#include "ds18b20.h"
 #include "main.h"
 #include "io.h"
 
@@ -9,9 +10,22 @@ void initIO()
     DDRD |= (1 << LED_1);
 }
 
+void readTemp()
+{
+    double d;
+
+	sei();
+    d = ds18b20_gettemp();
+    if (d >= 21)
+        PORTD |= (1 << LED_1);
+    else
+        PORTD &= ~(1 << LED_1);
+}
+
 int main(void)
 {
     initIO();
+    readTemp();
 
     return 0;
 }

src/ds18b20.c

@@ -0,0 +1,144 @@
+/*
+ds18b20 lib 0x02
+
+copyright (c) Davide Gironi, 2012
+
+Released under GPLv3.
+Please refer to LICENSE file for licensing information.
+*/
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+
+#include "ds18b20.h"
+
+/*
+ * ds18b20 init
+ */
+uint8_t ds18b20_reset()
+{
+    uint8_t i;
+
+    //low for 480us
+    DS18B20_PORT &= ~(1 << DS18B20_DQ); //low
+    DS18B20_DDR |= (1 << DS18B20_DQ); //output
+    _delay_us(480);
+
+    //release line and wait for 60uS
+    DS18B20_DDR &= ~(1 << DS18B20_DQ); //input
+    _delay_us(60);
+
+    //get value and wait 420us
+    i = (DS18B20_PIN & (1 << DS18B20_DQ));
+    _delay_us(420);
+
+    //return the read value, 0=ok, 1=error
+    return i;
+}
+
+/*
+ * write one bit
+ */
+void ds18b20_writebit(uint8_t bit)
+{
+    //low for 1uS
+    DS18B20_PORT &= ~(1 << DS18B20_DQ); //low
+    DS18B20_DDR |= (1 << DS18B20_DQ); //output
+    _delay_us(1);
+
+    //if we want to write 1, release the line (if not will keep low)
+    if (bit)
+        DS18B20_DDR &= ~(1 << DS18B20_DQ); //input
+
+    //wait 60uS and release the line
+    _delay_us(60);
+    DS18B20_DDR &= ~(1 << DS18B20_DQ); //input
+}
+
+/*
+ * read one bit
+ */
+uint8_t ds18b20_readbit(void)
+{
+    uint8_t bit = 0;
+
+    //low for 1uS
+    DS18B20_PORT &= ~(1 << DS18B20_DQ); //low
+    DS18B20_DDR |= (1 << DS18B20_DQ); //output
+    _delay_us(1);
+
+    //release line and wait for 14uS
+    DS18B20_DDR &= ~(1 << DS18B20_DQ); //input
+    _delay_us(14);
+
+    //read the value
+    if (DS18B20_PIN & (1 << DS18B20_DQ))
+        bit = 1;
+
+    //wait 45uS and return read value
+    _delay_us(45);
+    return bit;
+}
+
+/*
+ * write one byte
+ */
+void ds18b20_writebyte(uint8_t byte)
+{
+    uint8_t i = 8;
+    while (i--) {
+        ds18b20_writebit(byte & 1);
+        byte >>= 1;
+    }
+}
+
+/*
+ * read one byte
+ */
+uint8_t ds18b20_readbyte(void)
+{
+    uint8_t i = 8, n = 0;
+    while (i--) {
+        n >>= 1;
+        n |= (ds18b20_readbit() << 7);
+    }
+    return n;
+}
+
+/*
+ * get temperature
+ */
+double ds18b20_gettemp()
+{
+    uint8_t temperature_l;
+    uint8_t temperature_h;
+    double retd = 0;
+
+#if DS18B20_STOPINTERRUPTONREAD == 1
+    cli();
+#endif
+
+    ds18b20_reset(); //reset
+    ds18b20_writebyte(DS18B20_CMD_SKIPROM); //skip ROM
+    ds18b20_writebyte(DS18B20_CMD_CONVERTTEMP); //start temperature conversion
+
+    while (!ds18b20_readbit()); //wait until conversion is complete
+
+    ds18b20_reset(); //reset
+    ds18b20_writebyte(DS18B20_CMD_SKIPROM); //skip ROM
+    ds18b20_writebyte(DS18B20_CMD_RSCRATCHPAD); //read scratchpad
+
+    //read 2 byte from scratchpad
+    temperature_l = ds18b20_readbyte();
+    temperature_h = ds18b20_readbyte();
+
+#if DS18B20_STOPINTERRUPTONREAD == 1
+    sei();
+#endif
+
+    //convert the 12 bit value obtained
+    retd = ((temperature_h << 8) + temperature_l) * 0.0625;
+
+    return retd;
+}