Arduino 1-Wire Temperature Sensor Hacking
Posting not tagged on jan 28, 2010
So, I have an Arduino Duemilanove (wtf is wrong with those Arduino people and their board names?) and I decided it was time to get some progress with hacking the Dallas Semiconductor temperature monitors I got from Maxim IC.
The sensors are DS18S20 sensors, 1-Wire temperature monitors. Using them in the Arduino was made easy by Robin James’ OneWire library.
The pinout on the Arduino uses 1 digital pin, ground and +5.5V with a 4.7kΩ pullup resistor.
The schematics are as follows:
.-------------------.
o d0 a5 o
o d1 A D a4 o
o d2 R U a3 o
o d3 D E a2 o
o d4 U M a1 o
o d5 I I a0 o
o d6 N L |
o d7 O A vin o
o d8 N GND o R1
o d9 O GND o ___
o d10 V +5V o---|___|---o
o d11 E +3V3 o |
o d12 RESET o |
+------o d13 | |
| +--o GND | |
| | o AREF | |
| | | | |
| | '-------------------' |
| +---------------------------+ |
+-------------------------------)------+
| | ____
+------^---| | IC1
| +---| |
| | -|____|
| | ____
+------^---| | IC2
| +---| |
| | -|____|
| | ____
+------^---| | IC3
| +---| |
| | -|____|
| | ____
+------^---| | IC4
+---| |
-|____|
As you can see I can stack multiple sensors on the same 1-Wire bus. You can practically stack endless amounts of 1-Wire devices on this bus, as long as the bus can deliver sufficient power.
Some example code:
#include <OneWire.h>
...
void getTemperature(byte *addr) {
byte present = 0;
byte data[12];
int i, hByte, lByte, tRead, tSign, cTemp;
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, enable parasite power
delay(1000); // now we wait!
present = ds.reset();
ds.select(addr);
ds.write(0xEE); // read scratchpad
for ( i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
}
lByte = data[0];
hByte = data[1];
tRead = (hByte << 8) + lByte;
tSign = (tRead & 0x800);
if (tSign) { // test MSB
tRead = (tRead ^ 0xffff) + 1; // 2's comp
}
cTemp = (5000 * tRead);
if (tSign) {
Serial.print("-");
}
Serial.print(cTemp);
Serial.print("\n");
}
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