Temperarture sensors - using LM35 and displaying in Celsius

1. What OS? (Wheezy or Jessie)

2. What class/size SD card? (ex. class 10 16gb)

3. What Model Pi? (A+, A, B+, B, Pi2)

4. Please describe the bug / issue. Attaching any relevant screenshots would be very helpful! Thanks in advance.

First, looks like the temperature sensor can show only values in Fahrenheit - is it possible to add an option to convert and display either Fahrenheit or Celsius?

The second issue, is I’m having the TI’s LM35 sensor, which output precise voltage proportional to the temperature in Celsius (ie 0.25V for 25 Celsius, 0.33V for 33 Celsius, etc). Just using a simple python script I can read and display the temperature:

As I can’t find the LM35 sensors in Cayenne, but the TMP36 has very similar specs, I tried it. However the dashboard, besides showing the value in Fahrenheit, it’s totally off, looks like:

So the second request: is it easy to add a LM35 sensor? I may do this myself, using my python script, if you show me how…

Thank you.

Celsius has been a hot item lately. They are working on it so hopefully next release? As for the sensor, most of the sensors people post about have had a confirmation from the devs that it will be added, I can imagine this one will be the same.

Yes, as @ats1080s mentioned, ability to toggle between F / C being developed. Just to prove it here is a screenshot :slightly_smiling:

It will go out next release, so hang in there!


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@mac_ha ust ordered LM35, this has been added to our roadmap of devices to add.

@eptak I’ll let you answer question about possibility of adding a custom Python script to WebIOPi. …The ability to add custom python script is also on our roadmap, and a feature I’m super excited for because it will really open up the possibilities of Cayenne.

Moving to the ideas / suggestions category for Celsius / LM35 sensor.

I can’t wait for this!

Keen to see Deg C
And some custom tinkering will be nice
~ Andrew

Deg C on it’s way…I know you’ve been asking from the beginning ha.


@bestes Great news, waiting for the next release, as well as the Python custom scripting in the future. Keep up the good job!

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Custom Script : should work the same way as WebIOPi does, but with a better UX, related to Cayenne possibilities and all talented UI developers we have at myDevices :wink:

LM35 : Need to check the curve difference with TMP36, maybe you can try to use that one !

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He tried but it showed the -15.61 value. LM35 is here in office (freshly arrived from TI), ready for testing when device gets integrated.

Ok, sorry, I did not notice that. I will change the curve to make another one.

I know my question could be stupid, but why not have the unit globaly setted for the user ?
I’m french, so I’m used to have temperatures in °C. On all sensors. Having to set it to each sensor seems strange.
If I go on a forum, don’t want to set the language on a particular section, I want to change it on the whole forum.

Yes… How about in account settings etc have:

  • Locale
  • Language
  • Units could fall out if this like Deg C etc
  • Or set Deg F/C
    ~ Andrew


I am new around and I think I will stay for some time. This project is really great.

Back to LM35 and °C, I am also waiting for it :slight_smile:
Please notice that LM35 can mesure negative temperatures. You need for that to add 2 diodes to the GND so you shift voltage to the negative range (don’t know the english for that).
That means the calibration is different depending on the diode (i use 1N4148)

thanks for all what you do.


Note that diodes have a negative temperature Vf / -Deg C coefficient…
This might add into the accuracy if you are using a linear temperature sensor ?

In fact a few 1N4148 by themselves strung in series (for greater sensitivity) with a constant current (= a 10k resistor will do) make quite nice very linear cryogenic temperature sensor :slight_smile:

I am puzzled why more people don’t just use the DS18B20 since it is a digital device and does -55 Dec C up to + 125 and 0.5 accurate out of the packet with no calibration and 1/16 deg C resolution… And multiple units plug direct onto the Pi GPIO header in parallel.

~ Andrew


for me it is simple. I have some … bur I entirely agree with you.

Just for the curious…
Here is the 3 cent cryogenic probe. Or the general concept at least as fitted to an picaxe 08M A ‘cool’ thing with this is that the voltage Rises with INcreasing -ve temperature values. Use and calibrate at your risk but it is pretty linear and may help out someones home brew liquid N2 setup etc…

More mad ideas like those ones here:
~ Andrew

@eptak, any update on the LM35 sensor?