A few days ago I had run into a problem at work. The small Mitsubishi Air Conditioner had decided to take a cooling nap in the middle of the day. So my office, which is also the machine room at work was up around 85 degrees Fahrenheit. I was used to this sort of thing, summers bringing primary cooling systems to their knees, but this time I had a huge A/C unit in the ceiling that I elected not to have removed and left in place, just in case. So I turned it on, set it’s thermal controller to 70 degrees and the room temperature tumbled in about ten minutes. Right after the room temperature was normal, and I had service out to visit me about my little wall-mounted A/C unit, the damn thing started functioning normally again. The tables turned on IT, where for our users, this is what happens to them. They can sit there and struggle, and then we arrive and the machines behave themselves like nothing at all was wrong.

So I had the big A/C, and it’s smaller wall-mounted unit both running overnight and faced a problem. I want to know what the temperature is in my machine room without having to buy a TempPageR device. I had one long ago, and it was rather expensive. I looked on my desk and noticed my Raspberry Pi, just sitting there, doing nothing of consequence. I did a brief cursory search on Google, and I knew the Raspberry Pi had a CPU Temperature interface hidden somewhere, and I was happily surprised to find a website detailing how to use this exact feature in Python programming language to write a temperature log, and optionally graph it. It was mostly copypasta, adapting things I had found online pretty much by copy and paste and hammering them here and there to work. I have programming skills, but they are rather dated and rusty. Plus I’ve never used Python, specifically. So my first effort was successful, I got a 1-second temperature logger in place. I was rather happily satisfied with my efforts, but I knew I would not be happy with Celsius, but I knew the temperature was colored by the CPU in the Raspberry Pi itself, so the reported temperature was quite higher than the room temperature.
I started to tinker. First searching for the equation to convert C into F. So I got it, 115 degrees. When I turned on the big A/C device, and its thermal controller displayed the ambient room temperature in F, 74. So I did some math and subtracted a constant 44 degrees from the CPU temperature, which “calibrated” the CPU temperature to be a rough approximation to the room temperature. Some eagle-eyed readers may notice that my math is off, but after I had moved the Pi over to the server stack, I had to adjust for a higher CPU temperature because of it being further away from the wall A/C unit. So now I had a 1-second temperature logger. I turned on graphing, and the entire program crashed and burned, I wasn’t running the application in an X-Windows environment, so I tore the graphing library and code out because I was never going to use the graphing feature anyways.

That, of course, was not enough to replace the TempPageR device. I needed some alarm system to alert me to what was going on. I thought of some interfaces, email, SMS, iMessage, email-to-telephone-call cleverness and each thought brought me against different versions of the cliffs of insanity. I could have probably smashed and hacked my way to a solution involving some ghastly labyrinth of security settings, passwords hashed with special algorithms that are only available on ENIAC computer simulators that only run on virtualized Intel 8086 processors with the Slovenian language pack loaded and using the Cyrillic character set; An arrangement that was an epic pain in the ass. So earlier in the day, I had tripped over an app advertisement for Slack so that it could use incoming data from the Pingometer website. I have a Pingometer account, a free one because I’m a cheap bastard. The single pinger externally checks my fiber optic connection at work, keeping AT&T on their toes when it comes to outages. The Pingometer website uses incoming Slack webhooks. An incoming Slack webhook comes from some source that makes a really simple web browser call using HTTP. It wraps JSON into HTTP and sends the request to Slacks servers. Slack then does everything needed to make sure the message is pretty and ends up on the right Slack channel, on the right team; this was my alert mechanism.

So I did another Google search, found the intersection between Linux, Python, and Slack and some more copypasta and some tinkering and I had a Python app that displayed the room temperature in Degrees F, and made my Slack a noisy mess, as it was sending incoming webhook requests every second. One more tweak, which was a super-simple IF-THEN block, set my high-temperature mark at 90 degrees F and let it go.

There is something satisfying about being able to hack something together, cobble it actually, and have it work without blowing up on the terminal, blowing up Slack, or otherwise failing. So now I have a $35 Raspberry Pi running as a rough temperature alarm, it’ll send alerts to Slack and let me and my System Admin know at the same time over Slack. I’m quite happy with how it all worked out. No obnoxious email settings, ports, security frameworks, awkward and obtuse hashing routines, just a single JSON-formatted HTTP call and BAM. All set. An alarm, with a date and time stamp and a temperature, delivered right onto my iPhone with automatic notifications from Slack, so it wakes me up if I need it.

So anyways, without further ado, here is the code:

from gpiozero import CPUTemperature
from time import sleep, strftime, time
import json
import requests

# Set the webhook_url to the one provided by Slack when you create the webhook a
t https://my.slack.com/services/new/incoming-webhook/
webhook_url = ‘https://hooks.slack.com/services/####/#####’

cpu = CPUTemperature()

def write_temp(temp):
with open(“cpu_temp.csv”, “a”) as log:
log.write(“{0},{1}\n”.format(strftime(“%Y-%m-%d %H:%M:%S”),str(temp)))
if temp > 90:
slack_data = {‘text’: “{0},{1}\n”.format(strftime(“%Y-%m-%d %H:%M:%S”
),str(temp))}
response = requests.post(
webhook_url, data=json.dumps(slack_data),
headers={‘Content-Type’: ‘application/json’}
)
if response.status_code != 200:
raise ValueError(
‘Request to slack returned an error %s, the response is:\n%s’
% (response.status_code, response.text)
)

while True:
temp = cpu.temperature
temp = (9.0/5.0 * temp + 32) – 44
write_temp(temp)
sleep(1)

It has been forever since I’ve needed to program anything. Once I was done, and I saw it work the way I wanted it to, I was quite happy with myself. I haven’t felt this particular sense of accomplishment since my college years. It was quite a welcome feeling.