The way we manage to recover the temperature sensibility was placing temperature sensors to the hand (or Claw in the case of the prototype) and some RGB leds that lights up in different colors. By averaging the total temperatures we assign a specific color to each temperature. In this way when the object taken was between 0 to 10 degrees Celsius the hand its going to light up in a blue color, then when the temperature rises in 10 degrees the hand will become green, then pink, then purple and so on till it gets red in 100 degrees Celsius.
Our gripper was made from a budget of 130 dollars aprox, and was made from recycled materials, mainly aluminium and steel. The gripper was poured of resin and hand machined with a dremel to give the final finish.
Step 1: Lets Build Something! (Mechanics)
then we work the pieces by hand with a dremel to make them lighter and give them a more modern look in the end. Working with resin was really hard and time consuming.
Step 2: Electronics 1 (Installing the RGB Leds)
RGB leds are a kind of special leds that light up in red, green and blue light. Also you can make combinations of colors by light up two or more colors at the same time. We use the leds in digital mode so we only have 10 combinations of colors. We make this on purpose so the changes in temperature its going to be more noticeable for the user.
When we get the leds they came with a small datasheet like the one below. It was wrong!!! Actually we end up burning a lot of leds by connecting them wrong like in the datasheet. The real pins are: The longer lead is Ground and the others are the colors, NOT like the datasheet says.
Step 3: Electronics 2 (Temperature Sensors)
Te temperature sensors we use where the TMP-36, which came in a SO-16 package that is the same a small transistor came. This sensor works by sending a voltage corresponding to the temperature they measure. Depending of the temperature they are measuring is the voltage we obtain in the base of the sensor.
This sensor have a solid state technique to determine the temperature. This means that doesn't use mercury (like other devices), bimetallic plates or thermistors. Like in a diode that we know that the voltage resistance rises with the temperature as we amplify precisely the voltage in the sensor its really easy to generate a analog signal that is directly proportional to the temperature. This is basically how temperature is measure.
The characteristics of this sensor are this:
Size: TO-92 package (more or less 0.2” x 0.2” x 0.2”) with three pins
Temperature Range: 0.1V(-40°C) to 2.0V(150°C) But efficiency decreases after 125°C
Power Supply: 2.7V to 5.5V, and only consume 0.05mA of current.
The way we can know the temperature is this:
Temp in °C= [(Vout in mV)-500]/10
For example if we have a voltage in the base of 1V that means the temperature is:
Temp in °C= [(1000mV)-500]/10=50 °C
Step 4: Control
We make the control in some way that you can control all with only one arduino analog pin.
Our control looks like this:
Step 5: Getting All Parts Together
to download the files. The PCB in the image is the 3.5.
In the fritzing image, the ones in the upper left are voltage regulators for each servo, the ones in the upper right are mosfets to control the RGB leds, the one in the bottom left is a voltage regulator for arduino and the temp sensors, and finally in the bottom right two potencimeters to control temperature sensibility and two connectors, one for the temp36 sensors and one for the control.
Step 6: The Last Step, Attach to the Arm!
The arm attachment was made to fit my arm, having in mind that this part is just to demonstrate the principle of having the gripper mount in a real arm. We have to get someone without a hand and make a real attachment to his or her measures.
Step 7: Working!!!
Step 8: The Future!
We are really interested in develop technologies to help people and make her lives a little better.
The next step is to build a more human hand and add some electrodes to control the prosthesis like a real hand. But as you know is all about getting sponsorship to continue working. :P