I am using this library to get temperature from my two DS18B20 chips. I have tried using this code, the code in the library example and using the modifications on the first linked page and I still get weird results. Even with just one chip connected. Here is the example code unmodified:
#include <OneWire.h>
// OneWire DS18S20, DS18B20, DS1822 Temperature Example
//
// http://www.pjrc.com/teensy/td_libs_OneWire.html
//
// The DallasTemperature library can do all this work for you!
// http://milesburton.com/Dallas_Temperature_Control_Library
OneWire ds(10); // on pin 10
void setup(void) {
Serial.begin(9600);
}
void loop(void) {
byte i;
byte present = 0;
byte type_s;
byte data[12];
byte addr[8];
float celsius, fahrenheit;
if ( !ds.search(addr)) {
Serial.println("No more addresses.");
Serial.println();
ds.reset_search();
delay(250);
return;
}
Serial.print("ROM =");
for( i = 0; i < 8; i++) {
Serial.write(' ');
Serial.print(addr[i], HEX);
}
if (OneWire::crc8(addr, 7) != addr[7]) {
Serial.println("CRC is not valid!");
return;
}
Serial.println();
// the first ROM byte indicates which chip
switch (addr[0]) {
case 0x10:
Serial.println(" Chip = DS18S20"); // or old DS1820
type_s = 1;
break;
case 0x28:
Serial.println(" Chip = DS18B20");
type_s = 0;
break;
case 0x22:
Serial.println(" Chip = DS1822");
type_s = 0;
break;
default:
Serial.println("Device is not a DS18x20 family device.");
return;
}
ds.reset();
ds.select(addr);
ds.write(0x44,1); // start conversion, with parasite power on at the end
delay(1000); // maybe 750ms is enough, maybe not
// we might do a ds.depower() here, but the reset will take care of it.
present = ds.reset();
ds.select(addr);
ds.write(0xBE); // Read Scratchpad
Serial.print(" Data = ");
Serial.print(present,HEX);
Serial.print(" ");
for ( i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
Serial.print(data[i], HEX);
Serial.print(" ");
}
Serial.print(" CRC=");
Serial.print(OneWire::crc8(data, 8), HEX);
Serial.println();
// convert the data to actual temperature
unsigned int raw = (data[1] << 8) | data[0];
if (type_s) {
raw = raw << 3; // 9 bit resolution default
if (data[7] == 0x10) {
// count remain gives full 12 bit resolution
raw = (raw & 0xFFF0) + 12 - data[6];
}
} else {
byte cfg = (data[4] & 0x60);
if (cfg == 0x00) raw = raw << 3; // 9 bit resolution, 93.75 ms
else if (cfg == 0x20) raw = raw << 2; // 10 bit res, 187.5 ms
else if (cfg == 0x40) raw = raw << 1; // 11 bit res, 375 ms
// default is 12 bit resolution, 750 ms conversion time
}
celsius = (float)raw / 16.0;
fahrenheit = celsius * 1.8 + 32.0;
Serial.print(" Temperature = ");
Serial.print(celsius);
Serial.print(" Celsius, ");
Serial.print(fahrenheit);
Serial.println(" Fahrenheit");
}
and I get these results:
ROM = 28 18 9E CF 0 0 0 52
Chip = DS18B20
Data = 1 F8 FD 0 0 1F FF 8 10 EA CRC=EA
Temperature = 3836.00 Celsius, 6936.80 Fahrenheit
ROM = 28 6F 73 D1 0 0 0 54
Chip = DS18B20
Data = 1 F0 FD 0 0 1F FF 10 10 5A CRC=5A
Temperature = 3832.00 Celsius, 6929.60 Fahrenheit
No more addresses.
After using the modifications on that page I get different numbers, but still very strange:
ROM = 28 18 9E CF 0 0 0 52
Chip = DS18B20
Data = 1 F8 FD 0 0 1F FF 8 10 EA CRC=EA
Temperature = -32.50 Celsius, -26.50 Fahrenheit
ROM = 28 6F 73 D1 0 0 0 54
Chip = DS18B20
Data = 1 F0 FD 0 0 1F FF 10 10 5A CRC=5A
Temperature = -33.00 Celsius, -27.40 Fahrenheit
No more addresses.
This room is about 27C. When I hold a chip the number rises(as in gets closer to 0) so it's not just inverted or something.
When I use the Dallas Temperature IC Control Library I get these results:
Dallas Temperature IC Control Library Demo
Locating devices...Found 2 devices.
Parasite power is: OFF
Device 0 Address: 28189ECF00000052
Device 1 Address: 286F73D100000054
Device 0 Resolution: 9
Device 1 Resolution: 9
Requesting temperatures...DONE
Device Address: 28189ECF00000052 Temp C: -32.50 Temp F: -26.50
Device Address: 286F73D100000054 Temp C: -33.00 Temp F: -27.40
I am using the pullup resistor and using external power supply... What is goin on here?
Thanks