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Capacitive Touch Button Computer Mouse Hack

Mouse modified with capacitive touch button not only helps those with limited mobility (such as ALS), but also makes the mouse click silent

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The original idea to improve the computer mouse with capacitive touch sensor instead of mechanical micro switch is to help a friend with limited hand mobility due to ALS (Amyotrophic Lateral Sclerosis, also called Lou Gehrig's disease) to work from home. She needs to use a work station with professional software at home but her condition makes the clicking of a standard computer mouse a daunting task. This can also help those people suffering from Rheumatoid Arthritis or so called 'trigger finger' syndrome due to RSI (repetitive strain injury). These medical conditions lead to hand finger joints exhibiting a limitation of movements that makes mouse clicking difficult and painful.

Additionally it is sometimes desired to be able to use the computer mouse to make less obnoxious clicking sounds, such as during presentation in online video conferencing, or working in the same room with your spouse at home and a truly quiet working environment is desired.

[From Mayo Clinic] Amyotrophic lateral sclerosis (a-my-o-TROE-fik LAT-ur-ul skluh-ROE-sis), or ALS, is a progressive nervous system disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control.

Imagine your fingers are stiff and difficult to click the regular mouse button which requires you to lift up the finger and press down. The idea behind this capacitive touch mouse is to change the mouse click action to lateral movement of your finger in order to touch the surface of protruded electrodes. In this way zero click force is required, and requires much less hand muscle function. This is different than touch mouse on the market which still requires lifting up the fingers to touch.

The design is to hack a standard computer mouse with TTP223 capacitive touch sensor module, and to replace the mechanical microswitch for the left and right mouse buttons with the capacitive touch sensor. No other hardware or software modifications is required.  The modified mouse with capacitive touch buttons performs and functions in the same way as before.  

This project achieved the goal of hacking hardware to be more user-friendly and inclusive to all types of mobility. It is also beginner-friendly,  as all the parts can be sourced inexpensively online and does not require any especial tools or software.  

  • 2 × TTP223 Capacitive Touch Sensor Module
  • 1 × DELL MS-116T Wired Computer Mouse Other mouse can also be used, the wiring may be different but the concept is same.
  • 2 × IN4148 Diodes
  • 2 × M3-0.5 x 12mm Flanged Button Head Socket Cap Screw and Nut, 304 Stainless Steel Discrete Semiconductors / Diodes and Rectifiers
  • 2 × 3MM LED Copper Lamp Holder (optional) Round Panel Mount Display for LED

View all 7 components

View project log

  • 1
    Prepare the Mouse

    I modified the computer mouse with two different designs. The simple ways is to remove the original micro switch for the left and right mouse button, and use two M3 stainless steel screw as capacitive touch sensor electrodes at corresponding locations. This should work for most of the people. I also created another version that uses 3mm LED with metallic (copper) socket as touch sensor electrodes with LED as visual touch confirmation. This latter design allows one finger to control both left and right button with visual confirmation, and is more suitable with the consideration for the ALS patients. You can decide which one works for you.  

    Dell MS-116t wired mouse is chosen in this project as example because I happen to have several of them laying around. They are inexpensive, easy to work with, and have good quality and performance, and compatible with Windows PC, Apple iMac as well as Chromebook. It is based on PixArt PAW3515DB chip which can be found inside many of the computer mice. The same concept can be applied to variety of the computer mouse with minor modification to the wiring.

    Capacitive Touch Mouse
    Capacitive Touch Mouse Designs

    Step 1

    The first step is to dissemble the mouse by removing the bottom Teflon pads with a knife or small screwdriver, exposing the 2 Philips head screws underneath. 

    Step 2

    Once the screws are removed, the top and bottom of the mouse will separate easily.  Remove the printed circuit board and remove the left and right mouse button micro switches using disordering iron. 

    Step 3

    Drill holes at appropriate locations at the top mouse shell. The top mouse shell consists of two parts and can be separated. I will first drill a small pilot hole with two parts connected, then separately to make sure that I don't damage the top surface. Additional washers can be added between the top and bottom to make the mouse completely non-clickable. 

    Location of the touch electrode
  • 2
    Modify the TTP223 Module

    I purchased the TTP223 Module from Amazon, which needs to be modified to fit our needs. First a 30-33 pF capacitor needs to be added to the empty pad on the board to get appropriate touch sensitivity. Also by default these modules are in toggle mode with output signal active-high. According to the mouse circuit diagram, the right mouse button switch is active-low, therefore we need to make the TTP223 module output goes to the right mouse button active-low. This can simply be done by bridging the pads marked A on the module (AB=10). Also remove the SMD LEDs on the modules if optional external LEDs are going to be used. 

  • 3
    Wiring and Assembly

    First, connect the touch electrodes to the TTP223 modules by soldering a wire from the module to the base of the electrodes. A copper washer should be used if the M3 stainless screw is used as electrode, since the stainless steel can not be soldered. 

    We then need to connect the TTP223 modules to the +5V power and ground as well as the left and right mouse buttons on the computer mouse PCB. Below is complete wiring diagram with the optional touch button LEDs included, as well as the location of connection points to the micro switches pads on the PCB. Two IN4148 diodes are added between the outputs of the TTP223 modules and the button inputs on the mouse PCB to eliminate the false signal. 

    Schematics
    Schematics
    PCB Connection Points
    PCB Connection Points
    Finished Touch Sensor Module
    Finished Touch Sensor Module

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Bin Sun wrote 08/21/2021 at 04:02 point

This project is still ongoing. After successful testing of the prototype using the off-shelf TTP223 module, I'm going to make dedicated PCB with smaller footprint and better efficiency. Also I have made several of them and shared with people with hand mobility for testing. Stay tuned. 

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