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e-NABLE Hand Spidey Sensors

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e-NABLE Hand Spidey Sensors are designed for children with congenital limb amputations. It is designed to allow children to reach, grab, and interact within their environment.  

Technical Specifications: 

Step 1: Temperature Sensing
Adafruit had a 10k Ohm thermistor on a long lead and dipped in epoxy for durability for a low price. Place it on a small breadboard with a pair of NeoPixel LEDs and an ATTiny85 processor. This minimal cost approach, shown in the purple looking photo (please reference the website), was mounted on an Adafruit Screw Shield atop an Arduino UNO R3 board for programming purposes. The notion was that the ATtiny chip, (costing about $2.00 in quantity 10 from Jameco) was just enough and a bit more than necessary to do the job, low in size and power, and could fit on the back of the gauntlet of the hand (the forearm bracer part) behind the tensioner. The author designed the circuit and programmed the chip with a sigmoidal temperature mapping function (S-shaped input voltage to color brightness transfer function) so that the offset and range could be easily and smoothly adjusted. The author took the number generated by the sigmoid and used it to create red/blue colors with (255 - sigmoid value) going to the red component of the NeoPixel and (sigmoid) itself going into the blue - green set to zero (0). This made the LED glow blue in ice water, purple at room temperature, and red in hot coffee or hot water from the sink. In the photo you see the sensor at room temperature, with purple reflecting off the white breadboard.

Step 2: Touch Sensing
The jury is still out on how to do touch sensing on an e-NABLE hand. There are various approaches, each with their own advantages and disadvantages; perhaps a combination approach will eventually prove best. The author started with the notion of using Force Sensitive Resistors (FSRs) to complete the task. The author attempted to strengthen the sensors by hand design, and even went so far as to say this type of sensing is for delicate use and not your everyday play in the mud hand, FSRs fell short of the mark. A few other promising technologies were discussed within the e-NABLE group feed and some of those look really good for future and not-so future (now or nearly now) use. The author used the forum (www.electro-music.com) to view discussions around 3D printed enclosures, music controller shapes, and eventually stumbled across Arduino based capacitive sensors as a way of controlling music. It had two capacitive nodes and made a frequency modulated woo-woo.

The strings on the hand will be replaced with Adafruit stainless steel thread used for wearable electronics, which should be strong and smooth enough. In addition, conduct electricity from the fingers to the processor will be added. The author has been working on a prototype that senses capacitance and detects human hands, conductors, and insulators if they are big enough or actually flex the probe of the capacitor. The circuit has two nodes: ground and probe, and a capacitance created by the lines of electric flux that exist between the two nodes can be measured electronically with a resistor so that an RC circuit is formed. The Arduino digitally switches the input from low to high and measures the time it takes for the RC circuit to reach a high state, and then it does it again from high to low. This provides a time, which is reported as a long integer to the Arduino software. Arduino and Processing code for the dual capacitive music sensor application are attached here.

Step 3: Conclusion and Future Work
As to future work I plan to combine the two projects into one in full sized Arduino format, miniaturize the electronics and install it into a hand with conductive fingertips, and change the speaker to a haptic vibration motor. That will complete the project from an e-NABLE standpoint and it will then be documented it in another Intractable.

Step 4: Schematics Addendum
Please reference the authors website for the schematics diagram.

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as of: 
12/28/2015
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e-NABLE Hand Spidey Sensors