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June 12, 2012
about 2 years ago
It appears that proximity to the arduino matters afterall… The only explanation I can come up with is that the arduino has enough heat dissipation that it affects the readings of a sensitive sensor like the DS18B20.
That would be awesome ! At least I’ll know if I’m going crazy or not … :-)
By the way, I’m not using parasitic power and I’m using the latest version of the OneWire library.
Now I have three sensors as follows :
Two are on a tiny breadboard (the kind you sell here) and one is on the same breadboard as the arduino (pro mini). I’ve hooked up power to all three sensors (same power supply). The one-wire pin is pulled up with a 4.7k resistor on the breadboard that has the arduino. I can move the other end of the 1-wire bus from the sensor on the arduino breadboard to each of the sensors on the smaller breadboard; I get 74.8 F from the sensor on the arduino breadboard and 72.1 F, 72.3 F from the other two sensors. All the sensors are within 3 inches of each other and I’m careful to not touch or otherwise disturb any of them. This is very mysterious !! Thanks for your interest in my problem…
Different power supplies didn’t fix it…. and different arduino boards (pro mini instead of micro) didn’t fix it either.
I’ve tried different breadboards, longer/short wires, changed the location of the sensor, but nothing changed.
My last experiment was to put both sensors on breadboards, one on the same breadboard as the arduino (which is a mirco by the way) and the other on a different breadboard. The breadboards are still next to each other as close as possible. But the sensor that is on the same breadboard as the arduino always shows 2.3-2.5 F more… It’s driving me up the wall … next I’ll try different power supplies (same ground) and different arduino boards, to see if that makes any difference. I looked and looked on line but I can’t find any other resports of this same problem… My guess is that nobody has noticed this.
I have two of these sensors connected to an Arduino. One of them is right on the breadboard with the Arduino, the other is on a long wire (about 8 inches). The two sensors have about 2.3 F difference in their readings.
If I put both on the breadboard, or both on a long wire away from the breadboard, they are within 0.2 F of each other which is understandable. But why do I get a significantly higher reading from the one that is on the breadboard ?
I even tried a TMP102 and a DS18B20. Again one on the breadboard the other on a long wire and I get similar disrepancy in readings; i.e. the one on the breadboard always shows about 2.3 F higher reading.
Is there an explanation for this ? Thanks !
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