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Temperature Lamp

Works with

Any CircuitPython board with I2C (SDA/SCL pins)

Level: Starter Input: MCP9808 temperature sensor Output: NeoPixel strip that changes color based on temperature

What you'll build

A lamp that glows cool blue when it's cold, shifts through green, and turns warm red when it's hot. Reading the temperature becomes something you can see across a room. Leave it on your desk and you'll start to notice patterns — how the room warms up in the morning, or how it cools down when the window's open.

What you'll need

  • Any CircuitPython board with I2C (SDA and SCL pins)
  • MCP9808 temperature sensor breakout (Adafruit)
  • NeoPixel strip or ring (at least 1 pixel)
  • Jumper wires

Wiring

graph TD
    MCP9808_SDA["MCP9808 SDA"] --> BOARD_SDA["Board SDA"]
    MCP9808_SCL["MCP9808 SCL"] --> BOARD_SCL["Board SCL"]
    MCP9808_VIN["MCP9808 VIN"] --> V33["3.3V"]
    MCP9808_GND["MCP9808 GND"] --> GND1["GND"]
    NEO_DIN["NeoPixel DIN"] --> BOARD_D4["Board D4"]
    NEO_5V["NeoPixel 5V"] --> PWR["5V (or 3.3V)"]
    NEO_GND["NeoPixel GND"] --> GND2["GND"]

The MCP9808 and any other I2C sensors can share the same SDA and SCL lines — that's one of the advantages of I2C. Each device has its own address so there's no conflict.

The code

import board
import busio
import neopixel
import adafruit_mcp9808

# Set up I2C and the temperature sensor
i2c = busio.I2C(board.SCL, board.SDA)
sensor = adafruit_mcp9808.MCP9808(i2c)

# Set up NeoPixels
pixels = neopixel.NeoPixel(board.D4, 8, brightness=0.3)

def temp_to_color(temp_c):
    # Map temperature range 15°C–35°C to blue→green→red
    temp_c = max(15, min(35, temp_c))
    t = (temp_c - 15) / 20.0  # 0.0 to 1.0
    r = int(t * 255)
    b = int((1 - t) * 255)
    g = int((1 - abs(t - 0.5) * 2) * 180)
    return (r, g, b)

while True:
    temp = sensor.temperature
    color = temp_to_color(temp)
    pixels.fill(color)
    print(f"Temperature: {temp:.1f}°C → color {color}")

How it works

The MCP9808 uses I2C — a two-wire protocol that lets many sensors share the same two pins (SDA and SCL). You create a busio.I2C object and pass it to the sensor driver. The driver handles the low-level communication so you never have to think about it.

sensor.temperature returns degrees Celsius as a float. That's it — one line to get the reading. The MCP9808 is a precision sensor, accurate to ±0.25°C, which is why it shows up in so many real-world projects.

The temp_to_color() function maps a number range to a color range. The variable t slides from 0.0 to 1.0 as temperature goes from 15°C to 35°C, and that value drives the red and blue channels in opposite directions. This pattern — mapping one range of numbers to another — comes up constantly in CircuitPython projects. Learn it here and you'll use it everywhere.

Installing the libraries

Copy neopixel.mpy and adafruit_mcp9808.mpy from the CircuitPython library bundle to your board's lib/ folder. Also copy the adafruit_bus_device folder — it's a dependency needed for I2C communication behind the scenes.

Not sure how to get the bundle? See Installing Libraries.

Remix it

Remix idea

What if it displayed the temperature as a number instead of a color? → OLED Hello World shows how to put text on a small screen.

Remix idea

What if it beeped when the temperature got too high? → Simple Tones shows how to make your board produce sound.

Remix idea

What if it logged temperature readings to the internet over time? → Adafruit IO Basics shows how to send data to a dashboard.

Go deeper