How to send Pi CPU Temperature to i2c so Nixie can turn on fan when needed?

[FlaMike]

Can some please tell me the secret sauce for forwarding the Pi's CPU temperature as a sensor to control when the case fan will go on/off?

The Pi appears to have 2 i2c buses, and bus 1 has the Megabas & Relay Hat on it.

I can read the CPU temperature:

Thanks for you help!

[tagyoureit]

This can all be done in REM and is somewhere in the wiki, but for the life of me can't find it now. There is a generic device for reading the Pi cpu temp. You can feed this to a relay to turn the fan on/off.

[FlaMike]

I think I'm close, just by following the screenshots you posted. When I add the feed to the generic device & click save, the screen greys out & when it comes back a bit later, the feed portion goes away. Could this be because I've not defined any relays on the Hat yet?

BTW, REM does show the CPU temperature within a few degrees of the Pi command line, so I must have done something right.

[tagyoureit]

Could this be because I've not defined any relays on the Hat yet?

Yes, the feeds need a specific device to be sent to.

Also, if you didn't know, if you load up REM on a non-Linux box and set up these devices it will mock up fake values every few seconds. It's a good way to test out a dev environment before trying to work out all the kinks on your pad.

[FlaMike]

Got it! Working on setting up the fan relay & then will go back to the generic device setup. Exciting stuff!!!!

I am accessing the Nixie via a Linux box, but it's a dual boot beast. I can run windows & access REM from there. Will that do the trick? If I understand you comment correctly, I'm guessing that won't do the trick--I need to install REM on winders. Either way, I'm getting there, little by little.

[FlaMike]

The relays I anticipate using are now configured and toggle when I click them in REM. I'm running into a wall--same problem when I try to setup the feeds tab for the CPU temperature; screen greys out when I save & the feed lost when it returns. I may just be ahead of my headlights because the Pi is just sitting on my desk with nothing attached to it at the moment.

I'll look around the wikis & cogitate a bit. Still at least I can see the CPU temperature in REM.

[FlaMike]

@tagyoureit

I think I have it! I found a discussion that appears to have the solution I need. #405

In my case, I'm using relay 5 for the case fan, so I changed the return code slightly. If I set the temperature to be around the current CPU temperature, the relay clicks on & off :-)

I do have one other hopefully easy question... Sitting on my desk where the room temperature is about 70 F, the Pi's CPU temperature is about 110 F. What is a reasonable temperature for turning the case fan on/off?

Thanks again for your help, patience, & fabulous software!!

Have a wonderful holiday weekend!