Alexander Moulton Marie Hammer Xingwang Gao Andrew Robertson Team Lead Mechanical Engineer Electrical Engineer

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

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

Customer Needs and Specifications NeedSpecificationMetricIdeal Value Enhance text based communication Establish a voltage output linearly proportional to force applied while typing Linear relationship between force and voltage output Couple analog data with keystroke character Character data transmitted with analog data (Boolean) True System is able to measure a large range of input force Range of force (N) 0 to 10N Differentiate user input accurately Users are able to establish up to 8 distinct outputs while typing Number of output partitions 8 Use sensors with static outputVariation in output voltage under static load (dV/dt) dV/dt = 0 Output is independent of simultaneous keystrokes Variation in output voltage with and without concurrent loads on multiple keys (V) Compatible with modern PC/Laptop USB protocol used for communicationUSB communication (Boolean)True Output is readable by PC software Applications able to monitor USB port can be programmed to interpret and display the data received Pass/fail of Communication (Boolean) True

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

Micro Controller Conditioning Circuitry

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

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

Test Data Force (N)ΔV (mV) Variation in output voltage for 1, 5, and 10N test forces with a second key fully depressed Modified: y = Unmodified: y = %error m = ( – )/ * 100% = 9.04% ΔV << Vmax/(# of output partitions) 31mV << 3.7V/8 = 462mV

Test Data (cont.) Average typing force among users UserTrial 1Trial 2Trial 3Trial 4Trial 5 Alex (N) Marie (N) Xingwang (N) Andrew (N) Number of distinct partitions without feedback UserTrial 1Trial 2Trial 3Trial 4Trial 5 Alex Marie Xingwang Andrew Number of distinct partitions with feedback UserTrial 1Trial 2Trial 3Trial 4Trial 5 Alex Marie Xingwang Andrew 88788

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

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.