PIC32MX: Interfacing with Force Sensors from a Scale
Original Assignment
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Your assignment is to use four analog inputs to continuously read four force sensors taken from a bathroom scale, and to display them on a PC screen as bars whose length corresponds to the force at the sensors. You will use Processing for the PC data acquisition and graphics.
Overview
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Circuit
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Code
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The Processing portion of our lab involves 4 sections:
1. colorbars:
continuously displaying the force applied onto each force sensor by using 4 bars that will grow or shrink depending on the amplitude of mass (force). The bars will also show the amplitude of the mass by changing colors. When 0 or little force is applied, then corresponding bar is black colored, at the max force, the bar is orchid (pink) colored.
2. xy-plot:
continuously displays the x- and y- position of the center of balance calculated between all 4 sensors with a dot on a xy-coordinate plane. So, if the person shifts his weight to the right side of scale, then the dot will move to the right in the x direction. If the person shifts his weight to the front of the sensor, then the dot will move up in the y direction.
3. x-position vs. time:
continuously plots a dot for the x-position along a time axis. This plot will be useful to see how much the person shifts his/her weight to the left or right (sagittal plane) over time. Due to the window size and the speed of processing, the points will be plotted over a time period of about 20 seconds.
4. y-position vs. time:
continuously plots a dot for the y-position along a time axis. This plot will be useful to see how much the person shifts his/her weight forward or backwards (coronal or frontal plane) over time. The code for this section is essentially the same as the x-position but edited to show y-position.
General Notes:
Our code was written with the assumption that the inputs from the PIC (that initially comes from the 4 force sensors) will come in the form of a 4x1 array. It does not actually arrive in that form from the PIC, it actually arrives as a string of floats separated by spaces ending with a new line. The new line is deleted and the floats are extracted out, normalized between 0-255, and put into the "mass" array. All of the normalization, window dimension parameters, rectangle dimensions, etc. were set up with the 0-255 range and 1000x700 window size in mind. So if the values are not between 0-255 or the window size is altered, almost all of following code will be messed up. The x-position vs. time and y-position vs. time plots are not implemented as independent functions. The code for these plots are found at the very end of colorbars();.
Global Variables
//initialization of the serial variable that will hold the values sent from the PIC via RS232 import processing.serial.*; Serial[] myPorts = new Serial[1]; //the PIC will output 4 floats and we will first store the values into these 4 variables float input0; float input1; float input2; float input3; //dimensions of our window will be 1000x700 float window_height = 700; float window_width = 1000; PFont fontA; //initializing our text font //the main "mass" 4x1 array that holds the values continuously sent from the 4 force sensors //we will refer to this array as the "mass array" in our comments float[] mass = new float[4]; //window dimension variable that is used to make the bargraph. The bx and by variables are //used so that the bargraph section could be more easily formatted in case we change the //window size. float bx = window_width/2/8; float by = window_height/2/8; int index; //color variables used to indicate the amplitude of the force applied to each sensor color c0; color c1; color c2; color c3;
Main Setup Function
void setup() { index = 0; InitSerial(); smooth(); //splitting the window into 5 separate areas and filling them with a 102 gray color size(int(window_width),int(window_height)); fill(102); rect(0,0,window_width/2,window_height/3); fill(102); rect(0,window_height/3,window_width/2,window_height/3); fill(102); rect(0,window_height*2/3,window_width/2,window_height/3); fill(102); rect(window_width/2,0,window_width/2,window_height/2); fill(102); rect(window_width/2,window_height/2,window_width/2,window_height/2); //filling inside of the x-position vs. time and y-position vs. time plots with white color fill(255); rect(25, int(window_height/3)+29, int(window_width/2)-49, int(window_height/3)-59); fill(255); rect(25, int(window_height*2/3)+29, int(window_width/2)-49, int(window_height/3)-59); }