Build your own activity monitor with Arduino

RetroBand is an open source, ATmega328 powered activity tracker that pairs with your smartphone.

Over the last couple of years, the wearable technology market has experienced tremendous growth, particularly when it comes to health and wellness. When thinking of the latest and greatest fitness bands, companies like Jawbone, Fitbit and Nike typically pop into mind. However, despite its surge in popularity, the cost of owning such a device has become as a major barrier in adoption. That’s exactly why an Instructables user “GodsTale” has decided to take it upon himself to create a DIY activity tracker using an Arduino Pro Mini (ATmega328), a Bluetooth module, an accelerometer, a LiPo battery and some custom software from his smartphone, all housed inside a 3D-printed case. Total cost: Less than $30.


The Maker, who recently designed the RetroWatch, says that the device he calls the RetroBand has only one feature: collecting data through its built-in accelerometer and relaying it to his smartphone. An accompanying mobile app (available on Google Play) then analyzes the accelerometer data and provides an output of calories burned as well as steps taken to the user. Subsequently, GodsTale urges that “this shouldn’t be called a ‘smart band’ since it has only simple features.”

The Android app is comprised of four parts: an Android UI, a Bluetooth manager, a background service and an algorithm section.

“The Android app check steps using collected data provided from RetroBand Arduino. The algorithm of the app is not that complicated. If you have much experience to this area, you can replace it with your own algorithm. The app saves the calorie data, so you can see the progress it in a monthly/daily/hourly graph form,” GodsTale explains.


The Maker has established a system where the accelerometer data is checked 20 times a second by the device. The gadget then transfers data to the smartphone application once a second. From there, the Android app receives the information in a matter of two seconds and determines an interval that the user’s movement increases dramatically — the number of movement increases is the step count. Beyond that, the app calculates calories burned based on user’s weight and steps, along with accumulated monthly, daily and hourly data.

At the brains of the operation lies an ATmega328. The Maker selected the Pro Mini board as “it works well with 3.7V lithium-polymer battery and its size.” He also employed a USB-to-UART converter to upload its source code.


One drawback of the RetroBand is that it cannot save data given its limited memory capacity, which is the reason for pairing it to a smartphone. GodsTale has made his code available on GitHub, while its Android app can be downloaded from the Play Store. Want to save some money on your next wearable? Head over to the project’s official page here to get started.

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