Extra Digit Sensor

Tom emailed us in advance to let us know he would be coming to commission us to make him some textile sensors for his self-made prosthesis.

Flickr set >> https://www.flickr.com/photos/plusea/albums/72157700714739734

Design Experiment:

Wrap Around Style quick prototyping
Textile digit sensorTextile digit sensor

First prototype try-out
Extra digit sensor

Extra digit sensorExtra digit sensor

The prototype size is 55mm circumference (finger circumference is 67mm, so there are 12mm to stretch) and 50mm in total height. 3PP Body Loop material is added on the bottom to achieve fiction to the skin so it does not slip out easily.

Extra digit sensorExtra digit sensor

The top of the tube is made of neoprene tube with 45mm circumference to fit to the 3D printed finger tip part at the joint connection.
470mm fabric cable (made of synthetic leather in 2 layers) is added to the 3pp Body Loop material to carry the sensor lines. The lines are made of Karl Grimm silver coated copper thread, applied as bobbin thread straight stitch, and connected to 2.54mm header. As the stitches are made with 5mm distance, it is connected to 2 of the outer pin of the header, leaving the middle pin to be NC (Not Connected).

Extra digit sensor
The cable wraps around the hand in diagonal direction so it does not hang. The connection is brought to the wrist area to further connect with the Arduino Microview.

construction schematic

>> download construction detail PDF

Microview pinout

Testbreadboard circuit view

Link to the Arduino code>> https://github.com/KOBAKANT/KOBA/blob/master/COMMISSIONS/14-Extra_Digit/Sensor_display/Sensor_display.ino

Feedback from Tom after the first prototype and our responce:
– Die Idee mit dem Strip ist genial, aber das Material muss dehnbar sein, vielleicht auch Neopren? (meine Armbandglieder sind da fast überflüssig…)
The idea with the Strip is awesome, but the material must be stretchy, maybe neoprene? (my bracelet links are almost superfluous …) (google translate)

our response:
I also thought about it, and tried it, but the stretchy makes the conductive thread stitch wavy and it will not be robust enough when you use it for long time (I think)
Also, it should be to some extent water proof/resistant.

Extra digit sensorfeedback1

The prototype was designed to be worn like the left image with the neoprene breadboard band on the wrist (like watch) and connect the header to the breadboard, but I like the idea suggested by Tom (photo on the right)
Perhaps we can make it out of stretch material and leave loose cables inside to allow it to stretch.

– Das Neopren am Ende ist zu dick, es gehört weg. Dafür würde ich es (1,5mm Dicke) beim Rest verwenden, anstatt des Netzmaterials.
The neoprene in the end is too thick, it belongs away. For that I would use it (1.5mm thickness) with the rest, instead of the net material.(google translate)

Which part is too thick? A or B part? I can change it to thinner one. but other than thickness, does the size fit well? Does this hold the 3D printed part tight enough?

Zusätzlich sollte es am Grundglied, in der Handfläche frei sein, und somit nur das Mittelglied bedeckt. (so viel Haut wie möglich)
Habe nochmal als Beispiel einen Handschuh zugeschnitten… und eine Skizze gemacht zu den Überlegungen.
In addition, it should be free at the base member, in the palm, and thus only the middle member covered. (as much skin as possible)
Have again cut a glove as an example … and a sketch made to the considerations.(google translate)

Also, the cable from the motor has to go down to the micro view. I can add tube/channel to the finger sensor base fabric. In this case, I need to know exactly where the cable from the motor will come out in your final design, so the channel is in exact place. The connection to the printed board (Tom is printing his own board with 3D printer on the photo) has to be defined so motor and sensor can directly connect to it.
Limblink commission feedback3