I'm new to Arduino and physical computing. I'm trying to read a temperature using the Dallas 18B20 sensor. I'm using the following code that I found on this forum:
#include <OneWire.h>
/* DS18S20 Temperature chip i/o
*/
OneWire ds(10); // on pin 10
void setup(void) {
// initialize inputs/outputs
// start serial port
Serial.begin(9600);
}
void loop(void) {
byte i;
byte present = 0;
byte data[12];
byte addr[8];
if ( !ds.search(addr)) {
//Serial.print("No more addresses.\n");
ds.reset_search();
return;
}
Serial.print("R="); //R=28 Not sure what this is
for( i = 0; i < 8; i++) {
Serial.print(addr[i], HEX);
Serial.print(" ");
}
if ( OneWire::crc8( addr, 7) != addr[7]) {
Serial.print("CRC is not valid!\n");
return;
}
if ( addr[0] != 0x28) {
Serial.print("Device is not a DS18S20 family device.\n");
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("P=");
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();
}
This is the output:
R=28 16 F7 7D 1 0 0 9E P=1 8F 1 4B 46 7F FF 1 10 14 CRC=14
R=28 16 F7 7D 1 0 0 9E P=1 90 1 4B 46 7F FF 10 10 92 CRC=92
R=28 16 F7 7D 1 0 0 9E P=1 90 1 4B 46 7F FF 10 10 92 CRC=92
...
I'm sure this is exactly what it's supposed to output but how in the heck do I convert this output to a real temperature in either celsius or fahrenheit? Thanks.
I'm new to Arduino and physical computing. I'm trying to read a temperature using the Dallas 18B20 sensor. I'm using the following code that I found on this forum:
This is the output:
R=28 16 F7 7D 1 0 0 9E P=1 8F 1 4B 46 7F FF 1 10 14 CRC=14
R=28 16 F7 7D 1 0 0 9E P=1 90 1 4B 46 7F FF 10 10 92 CRC=92
R=28 16 F7 7D 1 0 0 9E P=1 90 1 4B 46 7F FF 10 10 92 CRC=92
...
I'm sure this is exactly what it's supposed to output but how in the heck do I convert this output to a real temperature in either celsius or fahrenheit? Thanks.
There's a datasheet here: http://pdfserv.maxim-ic.com/en/ds/DS18B20.pdf which tells you how to decode the 9 bytes (8F 1 4B etc.) coming back from the device. At a quick glance the first two bytes encode the temperature. Page 4 in the PDF gives you the gory details:
The DS18B20 output temperature data is calibrated in degrees centigrade; for Fahrenheit applications, a
lookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended
two's complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the
DS18B20 is configured for 12-bit resolution, all bits in the temperature register will contain valid data.
For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit
resolution bits 2, 1 and 0 are undefined. Table 2 gives examples of digital output data and the
corresponding temperature reading for 12-bit resolution conversions.
...
Andrew
I modified the above code to provide Fahrenheit output. it is easy to switch to celcius just comment out the appropriate line of code
#include <OneWire.h>
/* DS18S20 Temperature chip i/o
*/
OneWire ds(10); // on pin 10
void setup(void) {
// initialize inputs/outputs
// start serial port
Serial.begin(9600);
}
void loop(void) {
byte i;
byte present = 0;
byte data[12];
byte addr[8];
int Temp;
if ( !ds.search(addr)) {
//Serial.print("No more addresses.\n");
ds.reset_search();
return;
}
Serial.print("R="); //R=28 Not sure what this is
for( i = 0; i < 8; i++) {
Serial.print(addr[i], HEX);
Serial.print(" ");
}
if ( OneWire::crc8( addr, 7) != addr[7]) {
Serial.print("CRC is not valid!\n");
return;
}
if ( addr[0] != 0x28) {
Serial.print("Device is not a DS18S20 family device.\n");
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("P=");
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(" ");
}
Temp=(data[1]<<8)+data[0];//take the two bytes from the response relating to temperature
Temp=Temp>>4;//divide by 16 to get pure celcius readout
//next line is Fahrenheit conversion
Temp=Temp*1.8+32; // comment this line out to get celcius
Serial.print("T=");//output the temperature to serial port
Serial.print(Temp);
Serial.print(" ");
Serial.print(" CRC=");
Serial.print( OneWire::crc8( data, 8), HEX);
Serial.println();
}
I'm trying to use the above code with a DS18B20 tempature sensor in Arduino 18 environment, but I can't get it to work. It gets stuck in this loop:
if ( !ds.search(addr)) {
Serial.print("No more addresses.\n");
ds.reset_search();
return;
And just constantly prints out "No more addresses". I'm not sure where I downloaded the 1-wire library from. I think I may have an error in it - either that or it is not compatible with the latest Arduino environment. Any help would be appreciated. Thank you
-teedeeus
UPDATE: I discovered this morning I was using the wrong resistor, so no need to reply to this post. It's working. That's what I get for trying to choose a part in dim light - duh!