Pitch Plus is a project through the University of Pennsylvania's Penn Health-Tech initiative, specifically through the Medical Device Club.
Pitch Plus is a wearable device designed to help combat the onset of injuries in Little League baseball pitchers. A predominant cause of non-contact injuries in Little League baseball players is repetitive pitching, directly correlated with the amount of pitches. Amount of pitches refers to pitches per game, innings pitched per season, and months pitched per year. This is difficult to monitor without the bookkeeping of a professional organization. 5% of youth pitchers suffer a serious elbow or shoulder injury (requiring surgery, or retirement from baseball) within 10 years. We sought to create a wearable device for these athletes that would monitor pitch counter, as well as forced experience in the pitcher’s arm. In a rehab setting, this would be able to display force exertion during a pitch.
Pitch Plus utilizes a Teensy 3.2 (ARM core) microcontroller as its processor, and collects data from an ADXL377 accelerometer. The data is stored in an SD card, which is held onboard. The accelerometer has analog outputs for the X, Y, and Z axes, with an input range of ±200 g’s of force. The device is outfitted with a single LED, which indicates when it is ready to start collecting data.
The microcontroller uses its 12 bit analog-to-digital converter to poll the accelerometer every 500 milliseconds. The data is stored in CSV text files on the SD card, formatted by the microcontroller. Every time the microcontroller is reset, or turned off/on, it will begin to store the incoming data in a new text file.
The MATLAB .m file takes in the accelerometer data, and calculates an RMS acceleration value (‘net acceleration’) for each time sample, defined as follows: √(X^2 + Y^2 + Z^2). It plots the individual x, y, and z data, as well as the RMS value.
Pitch Plus also utilizes an onboard HC-505 Bluetooth module, which allows any stream of onboard data to be live-streamed via Bluetooth to an app developed by Adafruit, for live visualization. The data from the microcontroller is sent via TX/RX lines to the module.
Pitch Plus’ applications can vary, depending on need. Pitch count can be used in a live game setting, to keep count of the pitcher’s pitch count and allow a coach to limit the athlete’s play time accordingly, lowering the risk of injury. In a rehabilitation setting, the device relies more on its ability to monitor pitch force. It can be used to gauge changes in maximum acceleration before and after an injury, and throughout the recovery process. A strategy used by physical therapists in a rehabilitation setting is to have an athlete attempt to throw multiple pitches with the same level of force, and then a pitch at 50% of that force. This device provides an accurate reading for the clinician and athlete.
As a member of this project's team, I was responsible for the hardware, and aiding in the development of the data processing and analysis solutions. Other team members worked in data processing, and in writing the firmware.
Once the concept was proven to work on a breadboard, a PCB was developed for Pitch Plus. To limit errors in assembly, breakout boards were used for most of the major components and soldered to the PCB. A prototyping area was integrated into the PCB to allow for more sensors and circuit elements to be added in the future. Our next version of Pitch Plus plans to no longer utilize any breakout boards, and solder the IC’s directly to the board.