Quote:
Originally Posted by Mikesolar
If you do it the way Jeff did, make sure it is not a long run of wire. That phone cable is probably only 22g and a long run will change your resistance as well as power draw, and I think it is rated for 60C. There is 3 wire "belden" cable that is also shielded and has a higher temp rating.
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If he's using DS18b20 (1-wire temp sensor), and it looks like he is, the temperature conversion is done inside the chip itself, and a digital pulse packet is sent back down the cable, which is immune to variation of value due to resistance differences. If a pulse packet returns that has been mangled, it is 'refused'. There are specifications regarding how long the sensor wiring can be (approaching 100 meters) and the topology (all sensors should be in a serial layout). In my own house I'm running six 1-wire sensors, I have broken the layout rules by using three branches (bad, bad, bad layout), but I have kept the runs pretty short, and everything is running just great. As I was adding the last branch and it's sensor, I could tell that I was at the very edge of data integrity. So far (2-years later) all is well.
The 1-wire devices can run just using data and ground wires, which is very finicky, or they can use a three-wire setup (power, ground, data), which is very forgiving and easy to implement. I would not have been able to do my wacky three-branch system had I not used the three-wire setup.
Once you are in "Arduino-land", there is almost no difference in difficulty between setting up analog sensors and digital sensors. Cost differences are tiny. Accuracy is very high.
-AC