P10002: Dynamic Keyboard Phase I
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Generate Product Concepts

Table of Contents

Step 1. Clarify The Problem

As a team of 2 Mechanical, 2 Electrical, and 2 Industrial Student we are to come up with a way to bridge the gap between emotion and speech. We are given a Budget of $1500 and 22 weeks to complete this project. A single key is to be designed which will have a force sensor, speed sensor, and a duration sensor. Depending on the input to the key/button an output will be displayed signifying the "emotion". For example a hard fast hit of the button could represent; anger, excitement, aggression, ect.

Being able to relay emotion in a text will assist NTID students and the general population communicate more effectively. Having one more level of communication should help enhance conversations and eventually get rid of the miss communication on paper.

Dynamic Keyboard Product Concepts

Step 2. Search Externally

Potential sensor types: Force sensitive resistors (FSR) - These sensors are variable resistors composed of multiple (parallel) contacts brought together by an external force. The more force that is applied, the more contacts are connected. This results in a greater admittance. A typical example of use is to place this sensor in series with another resistor forming a simple voltage divider. A variable voltage will appear across the second resistor which increases as more force is applied. The actual relationship between force and resistance is dependent on the material, but is usually nonlinear (force vs. admittance is linear and can be used for easy calibration).

Capacitive switches - These sensors function by altering the capacitance of the component as the metal plates are physically brought together. Capacitance is inversely proportional to the separation of the plates. The means of measuring capacitance is somewhat more difficult than the FSR case. An R-C series circuit can be used to measure a time constant for a known resistance. In terms of an analog output signal (since capacitance is not really a signal), this would normally be the time it takes for the voltage to discharge through the resistor to 36.8% of its initial value or charge to 63.2% of its final value. Capacitive switches are normally used in touch sensitive displays and keyboards, however, they are typically not used as a scale in these cases(i.e. they function as normal switches with improved robustness and longevity).

Piezoelectric sensors - Piezoelectric sensors are typically composed of crystal and normally used to measure dynamic (sometimes quasi-static) forces. Unlike FSRs and capacitive, these sensors have a large range of linearity. As such, their output can be modeled as a voltage source directly proportional to the forces acting on it. This is largely due to the static nature of the sensor despite the forces applied, which also makes it a good option for rugged environments. The dynamic nature of the forces applied make it a potential choice for velocity sensing as well as force.

Alternative sensors: Photogates - These light sensitive sensors may be used for timing purposes. Velocity can be computed for a differential distance (known to be about 2-4mm on typical keyboards) over a differential time.

Other electronic components: Micro-controller (general) - The analog signal is to be translated into a digital value related to the force applied. Any micro-controller with analog to digital conversion capabilities can accomplish this. Additional requirements include serial or parallel communication with a PC, as well as a sufficient number of analog I/O ports to support a large (at least 26) matrix of keys for the future project. In addition, power via the computer interface would be preferable.

Potential layout: The typical layout consists of a 'stack' of sensors each capable of obtaining the required data without interfering with each other. Examples would include two photogates (one for initial contact time and the other for final contact time) to measure velocity over a FSR which records full contact pressure. An alternative may be a FSR placed on top of a piezoelectric sensor to measure force and velocity respectively, or perhaps the piezoelectric sensor can be shown to handle both variables equally well.

For the future, the keyboard matrix may be similar to the current one. A micro-controller may apply power to a single row and column of the matrix and record the analog data if appropriate (i.e. key strike event has occurred).

The individual keys will include of some form of tactile feedback. Examples include the familiar dome shaped caps used in membrane keyboards or the more responsive scissor-switched keys used in some keyboards.

Output: The output of the system should mimic the current keyboard's scan codes on key strike events. In addition, a 'data code' will also be sent either subsequently on the same channel or in parallel. These codes are typically two bytes long and the type of data will be identified by a unique code or the sequence will be implied (and must be understood by 3rd party software). The data will most likely be sent in parallel with the usual scan code to avoid complications with the current keyboard protocol.

Step 3. Diagrams & Schematics

Level 1 System Level Diagram

Step 4. Search Internally

Step 5. Explore Systematically

Step 6. Reflect on the Results and the Process

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