I am considering building a temperature logger. I have been looking at various temperature sensors. Among the IC versions there is one wire and a type that just gives a voltage level.

I would think that the advantage of one wire is that you don't need to worry about the sensitivity of your ADC though they are a little more expensive.

Any other advantages? I would think the voltage level versions rely on the accuracy of your voltage reference for the accuracy of the temperature.


I can see where the 1 wire versions are more complicated to interface but probably more interesting.


Do the one wire versions compensate for variations in the supply voltages (i.e. reference voltage)?

 

An inexpensive Maxim/Dallas DS18B20 12 bit sensor has 0.5C accuracy and simple one wire hookup. A cheap and easy Picaxe uP has a one wire command that makes using and programming trivial. Free samples too.

http://pdfserv.maxim-ic.com/en/ds/DS18B20.pdf

 

I use the ones with the 1 wire or an SPI interface built in. Saves a bit of code on the processor, as well as an ADC port time, allowing for faster response to other sensors.

Accuracy is the same or better with the digital output compared to the analog out going to uC's A/D and software calibration of the voltage read.

If you want degF and have a degC, the 9/5+32 is a quick calculation as well, sometimes one is cheaper than the other is the only reason I mention this.

 

Thanks everyone for the responses.

No! If you use a pic microcontroller for your ADC reading or any other ADC with the +Ref connected to the Vdd, then your system is RATIOMETRIC which means that small variations in Vdd will be automatically compensated and will not effect the ADC reading.

Cheers

Alberto

I do not understand Alberto. Everything I have read says that doing ADC with your VDD as a reference is fine but if you want real accuracy, then a more accurate voltage reference is needed.
How does that make a difference here?

 

spinnaker, in ratiometric measurements the measured quantity is proportional to a ratio of two voltages rather than an absolute voltage.
When both voltages are proportional to the same reference, the absolute value of the reference does not effect the ratio.

Cheers

Alberto

Ah got it! I see. It all makes sense now. Thanks.