Fuel Up While Working Out with the Step n' Snack Fanny Pack

The idea for the Step N' Snack

Exercise can be tiring, especially after a long day of walking and taking plenty of steps around the block. Rather than waiting until you get home to replenish your expended energy, YouTuber and maker Sam March created the Step N' Snack Fanny Pack device after receiving the suggestion from one of his Instagram followers. Originally, the pack would eject a peanut butter cup once a certain number of steps had been reached, but March wanted to go one "step" further and make the amount of candy proportional to the amount walked. The average person burns about one calorie for every 25 steps, and since a single M&M is equal to four calories, this special fanny pack would dispense one for every hundred steps taken.

Building a housing

The most important part of the device is the enclosure since it houses all of the sensitive electronic components. March milled a solid block of plastic with a CNC router to ensure a smooth, even finish on the outside, unlike a 3D printed part. There are three primary sections within: the PCB, an auger for moving the candy, and an M&M reservoir that can easily be topped up as you walk.

Counting steps

The microcontroller for this project is ESP32-PICO-D4 which was selected for both its processing power and BLE/WiFi connectivity options. March's step counting algorithm runs on the ESP32 and it continually reads new accelerometer data from the onboard LIS2DW12 3-axis IMU chip. Each step causes a small spike to appear within the data, as seen on the serial monitor graphing utility. This meant all the program has to do is count 100 of those spikes and then dispense a piece of candy.

How candy is dispensed

One major challenge that had to be overcome was how to fit a dispensing mechanism into such a small footprint that also required little power to operate. March came up with a solution that involves a tiny 3D printed auger that gets turned by a DC motor for about a second which causes a single M&M to get moved along and drop out the side of the enclosure. By using this solution, March was able to carefully control how much candy got dispensed at a time.

Using the Step N' Snack + future plans

March's video is well produced and has a lot of funny moments, including when he dons a set of bright pink sweatbands, short-shorts, and his custom fanny pack. As seen towards the end, the step counting algorithm works really well, and so does the dispensing mechanism. You can view the code and hardware files for the Step N' Snack project here on GitHub, and March plans on adding Bluetooth functionality that will allow users to view their total number of steps for the day.