Build a Raspberry Pi Home Temperature Monitor with MCP9808, InfluxDB & Grafana

After acquiring a Raspberry Pi and reviewing Eben Upton’s Raspberry Pi User Guide—especially the GPIO sections—I embarked on my first project: a home temperature monitoring system. This post details the initial iteration using a Raspberry Pi, an Adafruit MCP9808 breakout, an old Mac Mini, InfluxDB, Grafana, Python, and the runit process supervisor.

Sensor Hardware

For the temperature sensor I selected the MCP9808 breakout board from Adafruit. My choice was driven by:

• Native I²C interface – the Pi’s GPIO pins 3 (SDA) and 5 (SCL) support the required bus.
• Wide voltage range (2.7 V–5.5 V) – compatible with the Pi’s 3.3 V and 5 V rails.
• Cost‑effective – under $5 USD, ideal for a beginner’s first project.

Circuit Assembly

The MCP9808 board arrives mostly assembled; the only soldering required is attaching the 8‑pin header. I used a GPIO breakout and a breadboard to connect the Pi to the sensor, simplifying wiring and making future adjustments easier. The essential connections are:

• Power (VDD)
• Ground (GND)
• Data (SDA)
• Clock (SCL)

The remaining pins—used for address selection and alerting—were left unconnected for this single‑device setup.

Datastore

Capturing data over time allows for trend analysis and correlation with external events. I chose InfluxDB for its time‑series focus and intuitive query language. The database runs on an early 2009 Mac Mini (OS X 10.10) under Homebrew:

brew install influxdb

Configure the InfluxDB Database

After installation, I created a database and a dedicated user via the web console (default port 8083). I also set up a database named mcp9808_test to store the sensor readings.

Raspberry Pi Configuration

Enable I²C

The Pi does not load I²C modules by default. Add these lines to /etc/modules and reboot:

i2c-bcm2708
i2c-dev

Verify the sensor is detected with:

sudo i2cdetect 1

Sensor Software

I leveraged Adafruit’s MCP9808 Python wrapper, which also pulls in the I²C abstraction layer.

Install Build Dependencies

sudo apt-get update
sudo apt-get install build-essential python-dev python-smbus

Install the Adafruit MCP9808 Wrapper

cd ~/Downloads
git clone https://github.com/adafruit/Adafruit_Python_MCP9808
cd Adafruit_Python_MCP9808
sudo python setup.py install

Read, Report, Repeat

Below is the poll.py script that reads temperature every minute and writes the value to InfluxDB:

#!/usr/bin/python
import time
import Adafruit_MCP9808.MCP9808 as MCP9808
from influxdb import InfluxDBClient

# Prepare payload for InfluxDB
def temperature_data(degrees_c):
    return [
        {
            'points': [[c_to_f(degrees_c)]],
            'name': 'Temperature Readings',
            'columns': ['degrees_f']
        }
    ]

# Convert Celsius to Fahrenheit
def c_to_f(c):
    return c * 9.0 / 5.0 + 32.0

# Initialize sensor
sensor = MCP9808.MCP9808()
sensor.begin()

# Capture interval in seconds
capture_interval = 60.0

# Connect to InfluxDB (replace placeholders with actual values)
influxClient = InfluxDBClient('<influx-db-host>', 8086, 'mcp9808', '<password>', 'mcp9808_test')

# Continuous loop
while True:
    temp_c = sensor.readTempC()
    print('Temperature {0:0.3} F'.format(c_to_f(temp_c)))
    influxClient.write_points(temperature_data(temp_c))
    time.sleep(capture_interval)

Run the script as root to access the GPIO pins:

sudo python /path/to/poll.py

Process Supervision with runit

To ensure poll.py stays alive across reboots and power cycles, I configured runit as the process supervisor. Detailed setup steps are available in the original project documentation.

Summary

With the sensor, database, and monitoring stack in place, you now have a reliable, low‑cost home temperature logger. Use Grafana to visualize the data, set alerts, and gain actionable insights into your environment.