Thursday, March 12, 2015

Dallas DS1820

Well... I needed to use a long cable to acquire a couple of temperatures and I was having problems with the readings. The specs say that long cables can be used (something like 300 meters) and several devices, BUT reading some more I found out that these are supposed to have repeaters along the way. Nevertheless I found this information which I quote:
For short cable runs, unscreened two- or three-core cable, or single-core (parasite mode) or twin-core (normal mode) screened audio cable should be suitable. For longer cable runs, low capacitance cable such as rf aerial downlead (parasite mode) has been successfully used over a distance of 10 m. CAT 5 network cable has also been used with success over a distance of 30m, with data & ground using one twisted pair and power & ground using a second twisted pair. 
 I managed to put the DS1820 working with some cheating, and not using these recommendations, instead of the shielded cable and stuff, I used a pull-up resistor of 2000 Ohms, instead of the 4k7 which is usually recommended/used. It works, maybe the resolution is not the best, but in fact I'm not using all the cable I tested so, it's a cheaper way of doing what I wanted. The large distance was achieved in parasite mode, in regular mode the results would be even better.

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