Using a flex sensor as assistive technology

This page contains links and information for a flex sensor based assistive technology device that I am developing.


This project (Flex) is designed to fill a gap in what is currently available with off the shelf assistive technology. The system uses a short flexible plastic bend sensor. When the sensor is bent beyond an adjustable threshold, a switch signal is sent to a communication device.

Flex is designed to enable people who cannot use physical controllers such as buttons or joysticks but who can make an intentional movement with a finger or other joint. This motion can be measured with the flex sensor to enable interaction with switchable Augmentative and Alternative Communication (AAC) software.

Wearing a light and flexible flex sensor across a joint that can be intentionally moved enables a switch to be activated. This switch can control switchable software or a switchable device.

This is to help people who use switchable software to communicate and cannot access regular asistive technology devices such as buttons and joysticks.

First prototype

Information about v1 of the prototype is here: https://mattoppenheim.com/hand-wave/

Second prototype

I built a New and Improved v2 of the device and presented this at the online Communication Matters conference 2021.This consists of two parts.

There are two modules in the Flex system, a sensor module and a switch module. The flex sensor plugs into the sensor module via a lightweight and flexible lead. As the flex sensor is bent, an array of LEDs on the sensor module indicates how much the flex sensor is bent. Once a pre-programmed threshold of bend is exceeded, a trigger signal is sent from the sensor module to the switch module. The modules are shown below.

Flex sensor module connected to a flex sensor and a battery pack.
Flex switch module, connected to a laptop.

The switch module receives the trigger signal by a radio signal from the sensor module. A switch adapter cable connects the switch module with the communication device. The switch module generates a switch signal which passes through the switch adapter cable to control the switchable software or device. Grid 3 software was used for testing.

The amount that the flex sensor needs to be bent to send a trigger can be adjusted from either the sensor module or from the switch module. Having an adjustable threshold means that the system can be adapted for people with different ranges of movement.

A ‘pre-bend’ can be programmed into the system, so that somebody who at rest has a bent joint can use the system. This ‘pre-bend’ is set using a blue knob on the sensor module.

I sent a kit to East Kent Hospitals for testing on the request of one of their assistive technology team.

I made a video showing how to setup and use the kit here:

YouTube video

Written instructions are here:

user manual

Next iteration

I've been looking at a flex-sensor made by Bendlabs. Please find a post I wrote about this here.