I've been told 2 by a friend but this looks to only use one?


  • Two (SDA and SCL) and no additional pins when connecting other I2C (TWI) devices. – Mikael Patel Mar 22 '17 at 13:27

Below image is the answer to your question.


According to this image, magnetometer required four pins of arduino.

GND of magnetometer ----> Arduino GND

Vcc of magnetometer ----> Arduino 3.3 Volt

SDA of magnetometer ----> Arduino Analog Pin 4

SCL of magnetometer ----> Arduino Analog Pin 5

A4, A5 on Uno are SDA, SCL, required for hardware-based I2C.

I hope it will help you.

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It is I2C so 2 pins.

Optionally it can use a third pin to indicate data ready.

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It depends what you think of as a pin.

You have VIn and Gnd, SCL and SDA are the 4 main pins you will need to connect. The 3.3V and RDY pin don't seem to be connected in any of the pics I can see.

So the answer is 2 pins plus 2 power.

Oh from the page on how to use it, https://learn.adafruit.com/adafruit-hmc5883l-breakout-triple-axis-magnetometer-compass-sensor/wiring-and-test: "This 3-axis magnetometer breakout is thankfully very easy to use. It only requires 2 power pins and 2 data pins."

Interestingly it doesn't appear to use pull up resistors, which most I2C device require, so the might be built into the board.

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Here below image provides the connection and pin requirements for magnetometer...

Sensor Pins

According to image magnetometer will require 4 pins of Arduino 2 pins of supply i.e +3 volt and Ground and other two pins will be A4 & A5 pins of Arduino.

And to connect other sensors with Arduino, you can find datasheet of desired sensor and can find how many pins that sensor is going to use.

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