Added comments and changed labels of plot.

lab5/distance/main.c

@@ -1,11 +1,11 @@
 #include "msp430.h"
 
-#define   TRIG      BIT4
-#define   ECHO      BIT5
-
 #define   TXD       BIT2
 #define   RXD       BIT1
 
+#define   TRIG      BIT4
+#define   ECHO      BIT5
+
 #define   SOUND     34029         // speed of sound in cm/s
 #define   US        1000000       // microseconds in a second
 
@@ -33,23 +33,23 @@ void main(void) {
   P1DIR    &= ~ECHO;
   P1IE     |=  ECHO;
 
-  TACTL = TASSEL_2 | ID_0 | MC_2; // set timer to count up
+  TACTL     = TASSEL_2 | MC_2;    // set SMCLK timer to count up
   __enable_interrupt();
 
   while (1) {
     P1OUT |=  TRIG;               // start trigger signal
-    __delay_cycles(15);           // we need a >10 us pulse but one clock cycle is 1 us
+    __delay_cycles(15);           // we need a >10 us pulse and one clock cycle is 1 us
     P1OUT &= ~TRIG;               // end trigger signal
 
-    P1IES &= ~ECHO;
+    P1IES &= ~ECHO;               // interrupt on low to high
     __bis_SR_register(LPM0_bits + GIE);
     TAR = 0;
-    P1IES |=  ECHO;
+    P1IES |=  ECHO;               // interrupt on high to low
     __bis_SR_register(LPM0_bits + GIE);
     
-    TXByte = TAR;                 // time elapsed in us (approx)
+    TXByte = TAR;                 // time elapsed in us (no risk of overflow since echo will lower at 36000 us regardless)
     while (!(IFG2 & UCA0TXIFG));  // wait for TX buffer to be ready for new data
-    UCA0TXBUF = TXByte * SOUND / US / 2;    // curiously, this is a factor of 2 off
+    UCA0TXBUF = TXByte * SOUND / US / 2;    // distance in cm (curiously, this is a factor of 2 off)
 
     __delay_cycles(100000);       // wait 100 ms before measuring again
   }

lab5/distance/python-serial-plot.py

@@ -57,7 +57,7 @@ times=np.arange(0,50,1.0) # 50 from 0 to 49.
 
 #create a plot:
 fig = Figure()
-ax = fig.add_subplot(111,xlabel='Time Step',ylabel='Temp (deg F)')
+ax = fig.add_subplot(111,xlabel='Time Step',ylabel='Distance (cm)')
 ax.set_ylim(0,255) # set limits of y axis.
 
 canvas = FigureCanvas(fig) #put the plot onto a canvas
@@ -72,7 +72,7 @@ win.set_title("ready to receive data");
 
 line, = ax.plot(times,yvals)
 #open a data file for the output
-outFile = open("time_and_temp.txt","w")
+outFile = open("time_and_dist.txt","w")
 start_time = time()
 ser.flushInput()
 
@@ -84,7 +84,7 @@ while(1): #loop forever
         outFile.write(str(time()-start_time)+" "+str(yvals[49])+"\n") #write to file
         line.set_ydata(yvals) # draw the line
         fig.canvas.draw() # update the canvas
-        win.set_title("Temp: "+str(yvals[49])+" deg F")
+        win.set_title("Distance: "+str(yvals[49])+" cm")
     while gtk.events_pending():	#makes sure the GUI updates
         gtk.main_iteration()
 #    sleep(.05) # don't eat the cpu. This delay limits the data rate to ~ 200 samples/s