Connecting Sauna – How to make sauna call home

Last fall I got into playing with Ruuvitag sensors. Those are small, battery powered devices which measure temperature, humidity, pressure and acceleration. I placed one sensor to our sauna with and idea to make sauna call home: When certain temperature is reached, I’ll get a notification to my phone about sauna being ready to be utilized.

Ruuvitags are bluetooth beacons which broadcast measurements once in a second. Raspberry Pi has a bluetooth receiver built-in so it was a natural choice for listening the data stream. There is also a great Python library for Ruuvitags available which makes reading the measurements easy.

For notifications I’m utilizing Telegram messenger which I installed into my mobile. It’s an instant messaging app similar like WhatsApp or Signal. There’s a nice feature called bots which are basically third-party apps. The cool thing is that bots can be controlled using an API and that’s how I’m sending notifications to my phone. And there’s a Python library for Telegram also. What needs to be done in Telegram side is following:

  1. Create a bot
  2. Acquire token
  3. Acquire chatid

There are multiple how-to documents available how to do this and here’s one.

I made a Python script which listens the Ruuvitag data stream, parses temperature out of it and if certain temperature is reached, it will send a notification. Script utilizes a file to store timestamp of when the latest notification was sent. This timestamp combined with resend timelimit parameter is for not flooding the phone with notifications:

from ruuvitag_sensor.ruuvi import RuuviTagSensor
from datetime import datetime
import telegram
import csv
import sys

# Two command line arguments:
# 1. Temperature limit
# 2. Resend timelimit in minutes

macs = [''] # MAC address of a Ruuvitag
timeout_in_sec = 10
temp_limit = float(sys.argv[1]) # Temperature limit (Celsius)  which indicates sauna being ready to enter
temperature = 0
resend_timelimit = float(sys.argv[2]) # Resend timelimit in minutes
now = datetime.utcnow()
dt_string = now.strftime("%Y-%m-%dT%H:%M:%S.%fZ")

# Let's fetch the latest measurement (timestamp and temperature):
reader = csv.reader(
   open("sauna.csv"), delimiter=";")
for row in reader:
   latest_notification = datetime.strptime(row[0], "%Y-%m-%d %H:%M:%S.%f")
   prev_temp = row[1]

# Fetching data from Ruuvitag:
data = RuuviTagSensor.get_data_for_sensors(macs, timeout_in_sec)

for j in data:
     temperature = data[j]['temperature']
     print('Measured temperature: '+str(temperature))
     print('Temperature limit: ' + str(temp_limit))
     datediff_in_minutes = (now - latest_notification).total_seconds() / 60 # time difference in minutes between now and when latest notification was sent
     print('diff in minutes: '+str(datediff_in_minutes))
     print('resend timelimit: ' + str(resend_timelimit))
     # IF temperature is above limit AND time difference between now and when latest notification was sent is more than resend timelimit THEN let's send a notification:
     if temperature >= temp_limit and datediff_in_minutes > resend_timelimit:
          # Let's create a Telegram bot
          bot = telegram.Bot(token='')
          chat_text = 'Sauna valmis! Lämpötila: ' + str(temperature)
          bot.send_message(chat_id=chatid, text=chat_text)
          f = open("sauna.csv", 'w')
          with f: # Let's write latest measurement into a file:
             writer = csv.writer(f, delimiter=";")
             writer.writerow([now, temperature])

MAC address of Ruuvitag must be placed into line 11. Lines 39-40 are for Telegram token and chatid.

Script is scheduled using cron. Below’s a screenshot of an actual notification.

Sauna calls home

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