DS18B20 sub-zero temp readings


#1

Hi,

I’m trying to get a DS18B20 temp sensor to read values lower than zero, as in a fluid temp in a chiller unit, but on the dashboard it goes down to zero and then stops at zero. Any idea how I configure it to allow lower readings? According to the spec sheet it should read from -55 to 125C?

Thanks
Craig


#2

I’ll admit I haven’t tried this, but I’m curious if you can probe what values it is reading on the device since before sending to Cayenne (to see if this is a Cayenne issue with displaying the wrong value or a device configuration issue where it’s not even sending the expected value). If you let me know the device type I can help with how to grab that.


#3

It’s running on a RPi ver3, if you have an easy way to test it that would
save me some google time :wink: thanks


#4

I’d be curious about the output from the python script in the “software” section on this page: https://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing?view=all


#5

I agree with @rsiegel. I think you issue is in the format of you data before its sent. When I unhook my DS18b20 sensor my dashboard & MCU go to -196.00 so I know cayenne can display the data.


#6

Hi @craig.savage

I must admit, you made me curious and wanted to find out, as I am finishing a Home Thermostat, it definitely should be tested below 0 C…

So, I took my protoborad to the fridge, and stuck 3 DS18B20 probes inside the freezer, hah!
In just 15 minutes (system uptime), I was getting temperatures near -24 C, so Cayenne can handle it fine!

image

Some pictures, just for fun…

Paste your code, so we can have a look…

Cheers!
Marc


#7

Thank you for officially testing this @spacefolder !

~Benny


#8

Finally back home and able to tinker today, couldn’t get anything meaningful from the setup, so started by re-installing Raspian (new version from the site) and re-installing Cayenne. Like magic, it is now working fine… Thanks for all your help people, it was good to know it should work, certainly sped up the troubleshooting!


#9

Hey @craig.savage,

Just a heads up, we’re still working on providing ‘official’ support for the latest version of Raspbian that Raspberry Pi recently released. So, if you run into any issues, let us know, but that may be a reason if anything acts up.

Cheers,

~Benny