Wearable High Voltage Compliant Current Stimulator for Restoring Sensory Feedback

Abstract

Transcutaneous Electrical Nerve Stimulation (TENS) is a promising technique for eliciting referred tactile sensations in patients with limb amputation. Although several studies show the validity of this technique, its application in daily life and away from laboratories is limited by the need for more portable instrumentation that guarantees the necessary voltage and current requirements for proper sensory stimulation. This study proposes a low-cost, wearable high-voltage compliant current stimulator with four independent channels based on Components-Off-The-Shelf (COTS). This microcontroller-based system implements a voltage-current converter controllable through a digital-to-analog converter that delivers up to 25 mA to load up to 3.6 kΩ. The high-voltage compliance enables the system to adapt to variations in electrode-skin impedance, allowing it to stimulate loads over 10 kΩ with currents of 5 mA. The system was realized on a four-layer PCB (115.9 mm × 61 mm, 52 g). The functionality of the device was tested on resistive loads and on an equivalent skin-like RC circuit. Moreover, the possibility of implementing an amplitude modulation was demonstrated.

A Sensory Feedback Neural Stimulator Prototype for Both Implantable and Wearable Applications

“…Adding the third PCB to the implantable system, it is possible to adapt the system to a completely external and wearable scenario. The voltage compliance of the implantable system (14 V) is insufficient for the wearable scenario: as discussed in [38,39], high voltage compliance is necessary to adapt to variations in electrode-skin impedance, allowing the device to stimulate loads over 10 kΩ with currents of 5 mA. So, for external stimulation (i.e., TENS), it is mandatory to have a higher voltage compliance, which is achieved by adding the third board.…”