FlexiForce Pressure Sensor

1. FlexiForce Pressure Sensor Ben Nadeau Chris Hashem Megan Joiner

2. Objectives • To educate and help our peers to complete their project • To convert the output of an analog sensor to a digital input that can be read on a computer • Light an LED with either an Analog or Digital Output Channel • To calibrate our sensor in order to obtain a visual output using a Light Emitting Diode(LED)

3. Our Process

4. Our Sensor • FlexiForce Pressure sensor • The sensor acts as a variable resistance • The pressure applied to the sensor is inversely proportional to the resistance output by the sensor

5. Our A/D Converter • Arduino Mega microcontroller to do A/D conversion • Connects to the computer via USB • Has analog input pins • Outputs a digital signal to the computer that can be read in real-time

6. Arduino Mega Pin Outs

7. Original Schematic

8. Original Program #define SENSOR 0 // select the input pin for the // sensor resistor intval = 0; // variable to store the value coming // from the sensor void setup() { Serial.begin(300); // open the serial port to send // data back to the computer at // 300 bits per second } void loop() { val = analogRead(SENSOR); // read the value from // the sensor Serial.println(val); // print the value to // the serial port delay(100); // wait 100ms between // each send }

9. LCD Screen • Hooks up directly to the Arduino using schematic below • 2x16 LCD Screen • 16 Pin Interface • Register Select (RS) pin • Read / Write (R/W) pin • Enable Pin • 8 Data Pins • Display Contrast Pin • Power Supply Pins • LED Backlight Pins

10. Final Schematic

11. Calibration • Readout in Bits • To convert to Volts: • To calibrate, use equation: • Equation obtained from TekScan website • Ten LEDs divided over 1024 Bits determine light-up sequence

12. Program #define SENSOR 0 // select the input pin for the // sensor resistor #include <LiquidCrystal.h> //includes LCD library code // initialize the library with the numbers of the interface pins LiquidCrystallcd(32, 31, 25, 24, 23, 22); float val = 0;// variable to store the value coming // from the sensor float Bit=1023; //set value for amount of bits float volt=0; //set value to store calculated voltage float lbs=0; //set value to store calculated weight in pounds constintledCount = 10; //number of leds used intledPins[] ={ 2,3,4, 5, 6,7, 8, 9,10, 11}; //an array of pin numbers to which LEDs are attached. void setup() { lcd.begin(16,2); //sets up the LCD's number of collumns and rows reectively. lcd.print("weight in lbs:"); //rints message to LCD. for(intthisLed = 0; thisLed < ledCount; thisLed++) { pinMode(ledPins[thisLed], OUTPUT); } Serial.begin(9600); // open the serial port to send // data back to the computer at // 9600 bits per second } void loop() { val = analogRead(SENSOR); // read the value from // the sensor volt= val*5/Bit; //equation to convert incoming value to voltage lbs=24.2424*volt; //equation to convert voltage to pounds intledLevel = map(lbs, 0, 100, 0, ledCount); //map the result to a range from 0 to the number of LEDS // loop over the LED array: for (intthisLed = 0; thisLed < ledCount; thisLed++) { // if the array element's index is less than ledLevel, // turn the pin for this element on: if (thisLed < ledLevel) { digitalWrite(ledPins[thisLed], HIGH); } // turn off all pins higher than the ledLevel: else { digitalWrite(ledPins[thisLed], LOW); } } Serial.println(lbs, DEC); // print the pound value to // the serial port lcd.setCursor(0,1); //sets cursor to column 0 lin 1(second row since counting begins with 0) lcd.print(lbs); delay(100); // wait 100ms between // each send }

13. Resources / References • http://www.arduino.cc/ • http://www.tekscan.com/flexiforce/flexiforce.html • http://www.arduino.cc/en/Tutorial/LiquidCrystal • http://www.sparkfun.com/ • myweb.wit.edu/johnsont • Zach Baron