Building telemetry for tea aka Tealemetry
===
As a British person, I admittedly conform to the stereotype
of tea consumption, and giving I’ve been consuming tea for
most of my life I have gained opinions on all kinds of tea
based variables. The biggest one being the acceptable tea drinking
temperature.
So the thing is. Black tea (the best tea) needs to be
brewed with near boiling water to taste the best. But at the
same time this is incompatible with me being able to drink it
right away. On top of that because you have to wait for the
tea to cool down, it’s easy to forget about it, and then
it’s too late:
a graph showing the range of temperatures tea can be in
FLIR camera
Some people think that drinking tea at 30c or room
temperature is acceptable, I think _those people are incorrect_. However
after missing the acceptable temperature window too many times I
decided I need a way to be alerted when the tea is drinkable. I
got out my FLIR camera and confirmed that the heat spread over
a freshly brewed cup of tea is even at the bottom of the
mug.
a photo of a mug with a FLIR reading of 71C at the
bottom of the mug
This started me thinking. You could design a tea coaster
that can read the temperature of the mug sitting on it. So I
set out to make a coaster with a slot for a temperature
sensor, and under it, space for a ESP8266 as the microcontroller.
a 3d model of the tea coaster
Then used my flatmate’s 3D printer to print it out in
PLA:
MLX90616
Assembled together it looks like this (minus the ESP8266
being outside of the slot for debugging), the MLX90616 sensor
peeking out from the bottom of the coaster.
assembled coaster
final product
prometheus
After that, the ESP8266 setups up a web server that
exports metrics about the coaster temperatures in prometheus format,
with exceptional accuracy of 0.02c:
```
[ben@aura ~]$ curl xxx:9000/metrics
# HELP tea_mug_temp The point temp on the coaster.
# TYPE tea_mug_temp gauge
tea_mug_temp 24.689997
# HELP tea_ambient_temp the temp of the sensor.
# TYPE tea_ambient_temp gauge
tea_ambient_temp 27.490015
```
This means I can graph my coaster in grafana and watch
the mug get colder over time:
a grafana graph of tea temp
`max_over_time`
I can also then write a alert for when the cup of tea
is considered drinkable, `max_over_time` is used to ensure that
the alert for drinkability is not dismissed by me picking up
the mug to drink from it.
```
ALERT teaDrinkable
IF (max_over_time(tea_mug_temp[60s]) > 36) and
(max_over_time(tea_mug_temp[60s]) < 56)
FOR 1s
ANNOTATIONS {
summary = "The mug on the coaster is now
drinkable",
description = "drink it. or not. I'm an alert, not
a cop",
}
```
discord
alertmanager-discord
For me, my alerts are delivered to a discord chat room
via a alertmanager webhook translator I wrote for alertmanager
called alertmanager-discord
discord screenshot
The bonus of this is that I get phone notifications too
for this room:
screenshot of the discord mobile notification
internet of shit
Now, arguably you could include a LED to also signal when
it’s drinkable so that it’s not dependent on the internet for
notifications, but where would be the fun in that? Long live the
internet of shit.
If you want to build your own Tealemetry device, you can
find all of the ESP8266 source code and 3D printing models on
my github here: https://github.com/benjojo/Tealemetry
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