Good afternoon, Arduino comunity, I've seen several members with a problem about the delay of 750ms in the example code of OneWire, causing trouble in fast routines like PID's for example.
We found a solution for this delay by using a timer library: Arduino Playground - Timer Library and some additional fixments.
#include <OneWire.h>
#include <Timer.h>
Timer t;
OneWire ds(10); // on digital pin 10 (a 4.7K resistor is necessary)
byte i;
byte present = 0, present1 = 0;
byte type_s;
byte data[12];
byte addr[8];
float celsius;
void setup(void) {
Serial.begin(9600);
t.every(750, takeReading);
if ( !ds.search(addr)) {
// Serial.println("No more addresses.");
//Serial.println();
ds.reset_search();
delay(20);
return;
}
if (OneWire::crc8(addr, 7) != addr[7]) {
// Serial.println("CRC is not valid!");
return;
}
// the first ROM byte indicates which chip
switch (addr[0]) {
case 0x10:
type_s = 1;
break;
case 0x28:
type_s = 0;
break;
case 0x22:
type_s = 0;
break;
default:
return;
}
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, with parasite power on at the end
}
void takeReading() {
present = ds.reset();
ds.select(addr);
ds.write(0xBE); // Read Scratchpad
Serial.print(" ");
for ( i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
}
int16_t 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);
// at lower res, the low bits are undefined, so let's zero them
if (cfg == 0x00) raw = raw & ~7; // 9 bit resolution, 93.75 ms
else if (cfg == 0x20) raw = raw & ~3; // 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, ");
if ( !ds.search(addr)) {
ds.reset_search();
delay(20);
return;
}
if (OneWire::crc8(addr, 7) != addr[7]) {
// Serial.println("CRC is not valid!");
return;
}
// the first ROM byte indicates which chip
switch (addr[0]) {
case 0x10:
type_s = 1;
break;
case 0x28:
type_s = 0;
break;
case 0x22:
type_s = 0;
break;
default:
return;
}
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, with parasite power on at the end
}
void loop(void) {
t.update();
//_______________________________________________________________________________
// You make your routine here to make several times before reading sensor again
//_______________________________________________________________________________
}
We removed everything unnecessary from OneWire code and comments.
By Nuno Carreira and Victor Azevedo/Portugal - Madeira post
moderatore update: added code tags == # button above smileys.