I decided to make a fingertip sensor for my robotic hand. this small sensor has 5 resistive touch sensors and one temp sensor. can easily be connected to any robotic hand. the temp sensor is selected as a NTC thermistor, because it is very small and sensitive to 2 decimal digits and 5 DIY resistive touch sensors made of double sided sticky tape, self adhesive copper sheet and Velostat. I am still working on it but as far as I can see it can detect the force of grab and type of grabbed material as rigid and soft. further study is needed with collected data...
I updated my fingertip sensor after some tests... I realized that it performs better when placed on a soft flexible mount (just like in our fingers, skin over some flesh over the bones), some biomimetics worked well... I mounted my sensor on a silicon base and now its so sensitive and reactive... I used a small Arduino Nano to process the data. the resistors are 100K but I am planning to test the system with 1Megaohm ones for more sensitivity.
I wrote a Processing sketch to visualise the fingertip sensor data. by this you can see the temperature of the object in touch or environment, softness and hardness of the touched object and the amount of force exerted on it. this will enable to make some tests with the sensor. as far as I can see it is possible to detect the hardness of the touched object and you can control the force applied, which will make a robotic grabber to hold an egg without breaking it or dropping it...
-self adhesive copper tapes
-6 ea 100kOhm resistors
-double sided tape
-small sheet of Velostat
-DIY resistive touch-force sensor with 5 small touchpads
The tricky part of the project is building the touch sensitive pads small enough to fit on the fingertip. The tiny thermistor is chosen for the same purpose. I used double sided tape to fix the whole sensor together while soldering. the first layer is the voltage pad and then a small piece of Velostat is placed on to cover it. Later I made the outer actual touch layer where the 5 pads are placed in a compact spesific layout. After that I fixed the whole sandwich with another double sided sticky tape. the connection schematic is among the photos.
Version V1 was built on a hard PET piece to wear on a fingertip but later I realized that placing the whole sensor on a soft silicon base resulted in more resolution and sensitivity.
The simple code on Arduino reads the sensor values (all 5 touchpads and the thermistor) and sends it over serial. You can use this info to control a robotic hand or gripper to touch and hold things decently. I also wrote a simple Processing sketch to visualise the sensor data for testing purposes... All details can be found at my web site: