Lesson 4 of 5

Find an I2C sensor

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// Scan I2C1 for devices, then read the MPU-6050's ID #include <Wire.h> const byte MPU_ADDR = 0x68; // AD0 low: 0x68 const byte WHO_AM_I = 0x75; void setup() { pinMode(LED_BUILTIN, OUTPUT); Serial.begin(115200); Wire.begin(); // D14 = SDA (PB9), D15 = SCL (PB8) byte found = 0; for (byte addr = 1; addr < 127; addr++) { Wire.beginTransmission(addr); if (Wire.endTransmission() == 0) { Serial.print("Found device at 0x"); Serial.println(addr, HEX); found++; } } Serial.print("Devices: "); Serial.println(found); Wire.beginTransmission(MPU_ADDR); Wire.write(WHO_AM_I); Wire.endTransmission(false); // repeated start: keep the bus Wire.requestFrom(MPU_ADDR, (byte)1); if (Wire.available()) { Serial.print("WHO_AM_I = 0x"); Serial.println(Wire.read(), HEX); } } void loop() { digitalWrite(LED_BUILTIN, HIGH); // blink LD2 so you know it runs delay(500); digitalWrite(LED_BUILTIN, LOW); delay(500); }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

Scan the I2C bus on D14 (SDA) and D15 (SCL) and ask an MPU-6050 for its WHO_AM_I register. The Nucleo has no I2C pull-ups of its own, so the module has to bring them.

Tilt the module in the figure
The same two pins as an Uno R3's SDA and SCL
endTransmission() returns 0 when a device answers

Pin	Connects to	What it does
`D14`	The module's SDA	I2C data (PB9).
`D15`	The module's SCL	I2C clock (PB8).
`3V3`	The module's VCC	Power, 3.3 V.
`GND`	The module's GND	Common ground.

Wire it in

Sensors and actuators this board drives, with the real connections.

MPU-6050 IMUSupply 3.3 V
VCC on 3V3, SDA on D14, SCL on D15. The GY-521 brings the I2C pull-ups the Nucleo lacks.
Part pin Board pin
VCC 3V3Wire colour red
GND GNDWire colour black
SCL D15Wire colour yellow
SDA D14Wire colour blue
SSD1306 OLED displaySupply 3.3 V
A 0.96 inch I2C OLED runs at 3.3 V on D14/D15; most modules carry their own pull-ups.
Part pin Board pin
GND GNDWire colour black
VCC 3V3Wire colour red
SCL D15Wire colour yellow
SDA D14Wire colour blue

All 8 parts on the STM32 Nucleo-F401RE page

Connects to

What it does

D14

The module's SDA

I2C data (PB9).

D15

The module's SCL

I2C clock (PB8).

3V3

The module's VCC

Power, 3.3 V.

GND

The module's GND

Common ground.

Wire it in

Sensors and actuators this board drives, with the real connections.

MPU-6050 IMUSupply 3.3 V

VCC on 3V3, SDA on D14, SCL on D15. The GY-521 brings the I2C pull-ups the Nucleo lacks.

Part pin	Board pin
VCC	3V3Wire colour red
GND	GNDWire colour black
SCL	D15Wire colour yellow
SDA	D14Wire colour blue

SSD1306 OLED displaySupply 3.3 V

A 0.96 inch I2C OLED runs at 3.3 V on D14/D15; most modules carry their own pull-ups.

Part pin	Board pin
GND	GNDWire colour black
VCC	3V3Wire colour red
SCL	D15Wire colour yellow
SDA	D14Wire colour blue

All 8 parts on the STM32 Nucleo-F401RE page

Find an I2C sensor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Find an I2C sensor

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in