Biojoy Wristwatch

1. Overview | Download Project PDF


BioJoy is a interactive wearable biofeedback wristwatch that can help you relieve day-to-day stress by monitoring your stress levels and suggesting you alternatives to reduce / eliminate them within its owner's social context. It is a wireless Micro-Electromechanical system (MEMS) device with embedded blood pressure and accelerometer sensors whose combined output is a function of the emotional state and well-being of a person. The system is neural network learning dependent whose efficiency of outputting a correct emotional state value is increased by an interactive feedback mechanism from the person wearing it. This feedback system is a measure of how good a person actually feels as inputted by the person himself. The system can then use a combination of these feedback values and learned preferences [of what betters the emotional state of a person] to suggest alternatives to stress relief to the person through an embedded speaker at times when the stress levels reach certain values which are detrimental to the emotional well-being of the person.

The BioJoy wristwatch consists of the following physical and functional components:

1] Wristwatch Body and Protection Layer – This constitutes the primary body of the wristwatch and acts as a protection and foundation layer for other components.

2] Micro-pump Actuated Inflatable Polymer – This consists of a micropump actuated polymer that allows the wrist band of the watch to be inflated to a certain pressure level for blood pressure measurement. It is during its deflation that the blood pressure sensor output is meaningful.

3] Sensor-Actuator Electronics Mask Layer – This layer is 1/8th inch thick and houses the embedded blood pressure sensor, accelerometer sensor and custom electronics containing the microcontroller.

4] Increment-Decrement Push Buttons – These buttons constitute the input of the user interface and allow the user to interact with the device so that he/she can help BioJoy to refine its emotional state to stress level mapping [Section 7.2]. These inputs increase/ decrease the stress-emotion bars on the LED display thereby giving a visual indication of how the user is actually feeling at the current point in time.

5] Emotion Indicator LED Display – This display constitutes the output of the user interface and consists of emotion bars which are a function of the emotional state to stress level mapping (ESLM) of the user. It refreshes periodically to reflect the current value of ESLM and the user's current activity.

6] BioJoy Me Button – This button is pushed by the user when his ESLM value is low and he/she wants BioJoy to recommend a suitable stress relief alternative that would increase the ESLM value to an appropriate level. The user then operates the input buttons [4] to cycle through the displayed alternatives and the BioJoy Me Button again to accept one of them or simply nothing to reject them.

7] Built in speaker – This micro-speaker provides an audible interface to increase BioJoy's level of interactivity with the user by alerting him/her of ESLM values and to suggest stress relief alternatives.

8] RF Antenna / Bluetooth – This constitutes BioJoy's wireless interface to a user's computer or for communicating with other BioJoy devices in a wireless sensor network for yet to be planned functions.

9] Microphone – This component will allow the user to directly communicate with BioJoy through speech recognition software inside the microcontroller so that a friendlier user interface can augment the primary push buttons. The provision of this component will be made in BioJoy 2.0.

3. The Motivation

Developing wearable therapeutic biofeedback mechanism for stress and personal isolation relief. Many studies report significant blood pressure increase in subjects with cardiovascular problems when facing any source of mental stress. Mental stress in humans and other animals decrease cardiac electrical stability even in subjects with normal hearts. Premature ventricular contractions appear among subjects driving in heavy traffic and other stressful situations. Acute mental stress may provoke coronary artery vasoconstriction, reduce left ventricular ejection fraction, or induce or exacerbate left ventricular wall motion abnormalities in subjects with cardiovascular disease. In particular, "anger" among subjects with cardiovascular disease may leave them vulnerable to cardiac complications.

4. Functional Block Diagram


The basic functional block diagram of BioJoy is shown in the above figure. It consists of a blood pressure sensor and 3-axis accelerometer sensor. The blood pressure sensor output (oscillating signal) is a function of the emotional state measure of the person since blood pressure oscillations are related to the activity in the autonomic nervous system (ANS) which is known to be the central governing unit of a person's emotional state. The accelerometer sensor is employed so that the output of the blood pressure sensor is not distorted by the user's motion. The micropump actuator is activated by the microcontroller when a periodic emotional state measure is to be obtained by monitoring the blood pressure of the user. This activation results in electro-pneumatic inflation of the watch band (cuff from here on) which is an inflatable polymer that is inflated to the level of a micro-controller predetermined systolic blood pressure which is the peak pressure in the arteries. It is important to inflate the cuff to this level so that blood pressure can be determined since the blood pressure sensor can then monitor the mean arterial pressure (MAP) during the deflation cycle i.e. when the pressure in the cuff gradually decreases to its initial non-inflated state. The blood pressure sensor output (electrical voltage) is thus driven by sensing the arterial pressure in the user's wrist. This output can be visualized both in the time and frequency domains as a voltage versus time and voltage versus frequency graph. The sensor output is then signal conditioned and undergoes active motion

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