Following the same way we did with the MPU6050 article, we now have to design the component HMC5883L, which is a digital compass. Again, instead of drawing the part, you can use SparkFun’s library. Even if you use the component from the library, you can always practice and learn.
Last article, I wrote about how to use our own homemade Arduino Pro Mini bare bones along with an OLED display and how to make both of them consume as little power as possible. In fact, we managed to achieve a small 1.1 uA current with both of them sleeping. Also in our circuit there were a PCF8563 real-time clock module and one AT24C64 EEPROM memory. Now, to proceed with our smartwatch project we need to add sensors, such as an accelerometer, compass and pressure sensor. This article is about how to add them, read the variables and keep saving power.