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Most sensor gloves are designed as novel peripheral input devices only doing the most minimal, if any, on-board computation themselves and instead rely entirely on a host machine (PC) to make use of the acquired sensor data. The design novelty of the sensor glove described here is that it functions autonomously, acquiring sensor data, classifying hand gestures and wirelessly transmitting control signals and or sensor data using on board hardware, independent of a host machine. To accomplish this feat the glove incorporates a powerful micro-processor, five independent sensors, a high density light weight battery power supply and two independent wireless communication systems (IR and Bluetooth). Such design considerations allow the sensor glove to be used as an agile unconstrained controller, freeing the user from the typical confined and tethered user interaction space of a desktop. The sensor glove system was designed around a

standard, knitted fabric cotton glove. Cotton was chosen as it is comfortable, cheap and pliable, being easy to attach sensors and other electronic components. The glove was also designed with adjustability in mind, the chosen cotton fabric is inherently elastic allowing it to stretch to accommodate different size hands. The flex sensors are fixed to the glove only at the tip of the finger, with the remaining body of the sensor guided by elastic through holes at each of the finger’s phalanges. This mechanism allows the rigid flex sensors to tightly following the curvature of the fingers as they bend without compressing and opposing movement, see Figure 4.1.

Figure 4.1: Sensor glove: highlighting main components and joints.

4.2.1 Bend Sensor

The sensor used for acquiring finger position is a bi-directional flexible bend sensor (Flex Sensor – Spectra symbol Corp, Salt Lake City, USA), see Figure 4.2.

Figure 4.2: Sensor glove

The flex sensor exhibits a varying resistance that is proportional to its bend, with a nominal 25kΩ at rest and an intermediate resistance which is proportional to the applied bend radius. In order to sample and subsequently quantify this physical changing property of the sensor we need to convert the resistance into a varying voltage. This is accomplished by incorporating the sensor into a standard voltage divider configuration, with the output going to an analog-to-digital converter (ADC), see Figure 4.3. An

impedance buffer is also incorporated into the sensor acquisition circuit to reduce error caused by the source impedance. A voltage divider circuit and ADC channel are required for each flex sensor, totalling 5 for our design.

4.2.2 Micro-controller

In order to remove the dependency on an external PC, we based our system around a powerful embedded microprocessor, the PIC16f688 (PIC16f series, 8 bit micro-controller, Microchip corps, USA). We selected this microprocessor as it has the necessary function- ality and additional internal hardware required for our sensor glove design requirements. That is, five dedicated (ADC) channels, three digital I/O pins, one of which has pulse width modulation (PWM) support required by the IR LED and the remaining two having universal asynchronous receiver/transmitter (UART) support as required for the embedded Bluetooth module. The chosen PIC16f688 is a suitable micro-controller meet- ing all the above requirements; however an alternative equivalent micro-controller would suffice.

4.2.3 Communication Modules

The sensor glove incorporates two separate communication modalities, Infrared (IR) and Bluetooth (BT). IR is used for transmitting control signals to environmental devices such as home entertainment systems, including (TV’s, DVD players and radio/CD players). Most consumer electronics work on one of two wavelength: 870nm or (930-950)nm. To accommodate both, an IR LED of each wavelength was integrated into the gloves design. The IR LEDs are driven by Pulse Width Modulate (PWM) using a dedicated peripheral pin of the micro-controller.

Bluetooth is used for live streaming of sensor data from the glove to a host device at high speeds and can be used in conjunction with custom designed software for data capture and presentation, see Section 4.4. The Bluetooth module used is the (HC-05 Bluetooth Module - Guangzhou HC Information Technology Co., Ltd.). The BT module is connected over dedicated peripheral pins, a universal asynchronous receiver/transmit- ter (UART) module of the micro-controller.

4.2.4 Power

The entire system is powered by low voltage (i.e. 5V DC), using a 3.3V DC lithium polymer battery and a step-up DC to DC converter (NCP1402-5V, ON Semiconductor Components Industries, USA).

4.2.5 Electronic Schematics

The complete hardware schematics (electronic circuitry) are shown in Figure 4.3.

Figure 4.3: Electronic schematics for sensor glove system.

4.2.6 Safety

From a safety perspective, many considerations were made when designing the sensor glove. Cotton, which is an extremely good insulator was used for the main body of the sensor glove. Hence there is both good heat insulation, which protects the user from any heat dissipation from the electronic components, as well as good electrical insulation. In addition, the printed circuit board (PCB) which houses the electronic components rests on top of a thin layer of plastic, further isolating the user. Only very low voltages (i.e. 3.3 V and 5 V DC) are used to power the glove, which are of no danger to the user even if they came in direct contact with skin.

There are no moving mechanical parts used in the glove which is made from com- pletely docile material. The bend sensors incorporated into the glove are flexible and offer little or no noticeable resistance to movement. The PCB is attached to the body of the glove using Velcro—, hence, from a hygiene perspective all the components can easily be removed from the base glove which is machine washable. The glove is also comfortable to wear and easy to don and doff.