The Open Muscle Project Allows Users to Register Finger Movements with Hall Effect Sensors

Prosthetics

Those with mobility or dexterity problems find amazing benefits from using assistive prosthetic devices. However, the very analog nature of most of the products out there can leave users wanting something smarter and more capable. This is what inspired the Open Prosthetics team to develop their Open Hand and Open Muscle projects, which aim to greatly decrease the cost of prosthetics without sacrificing functionality. Their most recent development, the Open Muscle band, accurately detects muscle contractions in the forearm in order to control an artificial hand.

Designing the bracelet

The first and primary step in creating the Open Muscle project was determining the best method for quantifying muscle contractions. Many other approaches that have been used in the past involve placing electrodes near certain muscle groups and measuring their electrical activity. But due to potential interference and noisy data, the team instead opted to use a more mechanical system that revolves around spring-loaded pistons and magnets.

Measuring muscle contractions

Because the magnet can move closer or further away from the skin based on how much the contracting muscle displaces the piston, a Hall effect sensor just below can measure the change in the magnet's magnetic field. The analog values are then fed from the outputs of each of the 12 Hall effect sensors into an ESP32's built-in ADC pins. After being converted into a digital format, the data can then be plotted in real-time with a Python-based application.

Processing the data and future plans

Merely having lines on a graph with varying intensity values does not yield much usable information. Therefore, the team has been working on training machine learning models to correlate the data with finger and hand motions. Eventually, the goal is to have the capability to fully simulate a hand by just reading the bracelet's signals in hopes of controlling a robotic hand. For more information about the Open Muscle project, you can read the team's post here on their website or watch this demonstration video here on YouTube.