FES-demo-RPiPico

Code and circuit setup for Raspberry Pi Pico to demonstrate principle of operation of FES (Functional Electrical Stimulation)

Background

Functional Electrical Stimulation (FES) is an assistive technology commonly used to help overcome ‘drop foot’ by stimulating the peroneal nerve though skin surface electrodes contracting the tibialis anterior and lifting the foot. A pressure sensing ‘footswitch’ is also worn under the patient’s heel so that the stimulation can be applied with correct timing as the patient walks.

Demo Circuit

This basic, low cost circuitry demonstrates the principle of operation of an FES device as it would function to alleviate 'drop foot'. It makes use of a Raspberry Pi Pico microcontroller programmed in Micropython. The demonstration simulation can be found on Wokwi (https://wokwi.com/projects/352395885318022145)

Here, the footswitch is represented by a push button and the foot is represented by a servo motor which is in a dropped position when unstimulated and lifts to a dorsiflexed position when stimulated.

LED flashes as indicator that 'stimulation' is being applied to lift foot, triggered by releasing the load from the footswitch.

Instructions for Wokwi Simulation:

1. Start the Simulation

2. Press and then release footswitch

3. On RELEASE of the footswitch the foot lifts from a dropped to a dorsiflexed position and the LED lights

4. On pressing footswitch again or leaving it unpressed for a specified timeout period (2.5s default), the 'stimulation' ends, LED switches off and the foot returns to its dropped position

Next developments:

1. Introduce more timing parameters such as rising, falling ramps and extension time.

2. Incorporate screen to enable visualisation of parameter settings, status of inputs/outputs etc