Programmable and Flexible Stimulator for Neuromuscular FES 

Abstract

This paper presents the design of a programmable and flexible stimulator that generates biphasic stimulation waveforms for neuromuscular Functional Electrical Stimulation (FES). The FES device facilitates muscle contraction in the paralyzed limbs of spinal cord injury (SCI) patients by delivering low electrical pulses through electrode pads. A major challenge in FES-induced muscle contraction is early muscle fatigue, which significantly limits activities such as FES-assisted standing and walking. The use of a fixed stimulation pattern, typically a rectangular waveform, repeatedly activates the same motor units, leading to overwork and rapid fatigue. To address this limitation, this work proposes a programmable and flexible stimulator using an Arduino Mega 2560 microcontroller and biphasic output current source circuits. The stimulator allows for adjustable stimulus parameters, including biphasic output current (0–100 mA), pulse width (2 µs–20 ms), and frequency (20 Hz–2 kHz). Additionally, the system supports multiple waveform shapes, including rectangular, ramp-up/down, triangular, trapezoidal, exponential up/down, and burst pulses. The biphasic output current circuit was chosen for its safety advantages, as it prevents residual charge accumulation on the electrodes, reducing the risk of skin burns. The proposed design was first simulated using Proteus 8 software before being implemented and tested on hardware. The simulation and hardware measurement results confirmed and validated the stimulator’s functionality, demonstrating its ability to meet the specified design requirements.