P10002 Dynamic Keyboard

1. P10002 Dynamic Keyboard Alexander Moulton Marie Hammer Xingwang Gao Andrew Robertson Team Lead Mechanical Engineer Electrical Engineer Electrical Engineer

2. Project Goals • The purpose of this project is to capture key-strike dynamics for integration into a full keyboard • Enhance text based communication by providing an analog signal in parallel with binary keystroke data • Accurate differentiation of typing forces applied • Encapsulate typing forces with keystroke data and communicate with a PC • Characterize human typing forces for future projects

3. Revised Project Goals • Original project goal: • capture emotion while typing • Complications: • Keyboards are binary devices • Users are not trained to pay attention to how they type • Revisions: • No association between emotion and typing patterns • Conscious user input expected

4. Customer Needs and Specifications

5. Design Concept - Electrical • Analog data acquisition is independent of the original keyboard design • Four stages: • Thin film pressure sensitive device acts as a variable resistor in a voltage divider • Conditioning circuitry • Analog to digital conversion • Communication

6. Conditioning Circuitry Micro Controller

7. Design Concept - Mechanical • Keys: scissor switch, buckling, dome spring • Materials: ABS plastic, silicone, foam • Methods of Manufacturing: re-fabrication of current keyboard, rapid prototyping with ABS plastic, injection molding, machining raw material

8. Test Plan • Sensors have a static output (i.e. no capacitive loads) • Load a sensor with a static weight and measure any variation in the output over time • Establish a voltage output linearly proportional to force applied while typing • Calibrate device output (Voltage vs. Force) using weights ranging from 100g (~1N) to 2kg (~20N) • A linear best-fit line should be possible • Force transmitted through the key to the sensor matches the force applied at the top of the key within ±10%. • Calibrate the device output with and without the key and spring • Output of key strikes must be independent of simultaneous key strikes • A test key is loaded with a static force while a second key is fully depressed • The variation in output voltage with and without the second key being pressed is measured • Characterize human typing force • Objective is to establish a baseline of normal typing force for future reference • Result are compared with results from previous studies in typing force (1N to 2N) to ensure device accuracy • determine the resolution of human typing force • Objective is to determine the minimum amount of force a user can consistently increment • Tap key with successively increasing force average difference between keystrokes is measured

9. Test Data Modified: y = 0.002701 - 0.046 Unmodified: y = 0.002477 + 0.148 %errorm = (0.002701 – 0.002477)/0.002477 * 100% = 9.04% ΔV << Vmax/(# of output partitions) 31mV << 3.7V/8 = 462mV Variation in output voltage for 1, 5, and 10N test forces with a second key fully depressed

10. Test Data (cont.)

11. Meeting Specifications • Establish a voltage output linearly proportional to force applied while typing - PASS • Couple analog data with keystroke character - PASS • System is able to measure a large range of input force - PASS (0 to 13N) • Users are able to establish up to 8 distinct outputs while typing – Not met, only 6 levels were achieved • Use sensors with static output - PASS • Output is independent of simultaneous keystrokes – PASS • USB protocol used for communication - PASS • Applications able to monitor USB port can be programmed to interpret and display the data received - PASS

12. Future Project Recommendations • Printing Force Sensitive Resistors in a matrix underneath the keys for future keyboards • Designing modified keyboard to hold more circuitry as an alternative to modifying the keyboard.