MCP9808 on OLED: Precision Temperature
Overview & Wiring
What it is: The MCP9808 is a high-accuracy digital temperature sensor (±0.25 °C typical, 0.0625 °C resolution) over I2C. It's the sensor to reach for when you need lab-grade temperature, not weather-station "close enough".
How it works: Pure I2C, so it shares SDA/SCL with the OLED. The Adafruit library reads the calibrated temperature register directly in °C.
Wiring (shared I2C bus with the OLED):
MCP9808 SDA -> GPIO4
MCP9808 SCL -> GPIO5
MCP9808 VDD -> 3V3
MCP9808 GND -> GND
OLED VCC=3V3, GND=GND, SDA=GPIO4, SCL=GPIO5
Libraries: "Adafruit MCP9808" (installs "Adafruit BusIO"), plus "Adafruit SSD1306" and "Adafruit GFX Library".
On screen / Serial: temperature in °C with two decimals.
Gotchas: Default address is 0x18. The three address pins (A0–A2) let you put up to eight on one bus (0x18–0x1F). If begin() fails, check the address jumpers.
Circuit Diagram
Parts You Need
Source Code (Arduino / ESP32)
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_MCP9808.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
Adafruit_MCP9808 mcp = Adafruit_MCP9808();
void setup() {
Serial.begin(115200);
Wire.begin(4, 5);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
if (!mcp.begin(0x18)) {
Serial.println("MCP9808 not found");
display.setTextColor(SSD1306_WHITE);
display.setCursor(0, 28); display.println("MCP9808 not found");
display.display();
while (1) delay(10);
}
mcp.setResolution(3); // 0.0625 °C, ~250 ms/read
}
void loop() {
mcp.wake();
float t = mcp.readTempC();
mcp.shutdown_wake(1); // low-power between reads
display.clearDisplay();
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.println("MCP9808");
display.setTextSize(3);
display.setCursor(0, 24);
display.printf("%.2f", t);
display.setTextSize(2);
display.print(" C");
display.display();
Serial.printf("Temp: %.2f C\n", t);
delay(500);
}