Ads1299

The experimental setup is shown in Figure 3. First, an EMG board comprising ADS-1299 (Texas Instruments [27 ]) and Nucleo-F767ZI (STMicroelectornics [28 ]) was designed. We used a commercially available EMG chip to sample a set of EMG data at $$1 \mathrm{kHz}$$ and transferred the data to a computer through a USB interface. Second, an FES device (RehaStim, Hasomed) was utilized to apply electrical stimulation. Finally, a Kendall hydrogel electrode (Covidien) and ValuTrode electrode (Axelgaard Manufacturing) were utilized for EMG and FES, respectively.

For data collection, we fabricated a custom wireless 8-channel surface EMG data acquisition armband, as shown in Figure 1. The armband’s electronics is a derivative of the OpenBCI Cyton (OpenBCI), miniaturized to a 19 mm by 22 mm footprint. We use an ADS1299 (Texas Instruments) as our analog front-end (AFE) for signal amplification and analog-to-digital conversion, and an nRF52832 (Nordic Semiconductor) microcontroller for wireless data streaming. Our armband’s system can stream 8 channels of 24-bit EMG readings at 1,000 Hz wirelessly to USB dongle that forwards the readings to a host PC, smartphone or virtual reality headset.
Our armband’s electrodes are dry electrodes 3D-printed from electrically conductive carbon-black infused thermoplastic polyurethane (TPU), PI-ETPU 95–250 Carbon Black (Palmiga Innovation). The electrodes are circular in shape with a diameter of 14 mm and have brass snap fasteners. We 3D-printed a flexible armband using Shore 98A TPU to house pairs of electrodes circumferentially, and connect the electrodes using snap fasteners wired to our wireless EMG system. A more thorough description of hardware design and characterization of the electrodes, including dependence on mechanical grounding with the skin, may be found in Prechayasomboon and Rombokas (2023) .