Diff: measurement.h

Revision:

0:2dbd366be5fd

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/measurement.h	Mon May 07 16:14:45 2012 +0000
@@ -0,0 +1,70 @@
+/***********************************************************/
+/*Constants                                                */
+/***********************************************************/
+
+#define ISENSOR_SLOPE 23.9 //slope of the current sensor in [A/V]
+#define Y_INTERCEPT -60.1563 //sensor voltage at 0 current
+#define NUM_HALF_CYCLES 4 //set the number of ticks over which to measure speed
+#define WAIT_BEFORE_SPEEDSTOP 7.5 //amount of time to wait before declaring that the motor is not moving. 7.5s corresponds to a speed of 1 rev/min
+#define R1 200000//voltage measurement resistor connected to device under measurement [Ohm]
+#define R2 100000//voltage measurement resistor connected to ground [Ohm]
+
+/***********************************************************/
+/*Variables                                                */
+/***********************************************************/
+
+float end, begin, current_read;
+int current_state;
+int count = 0;
+
+Timer speed_timer;
+
+/***********************************************************/
+/*Pin setup                                                */
+/***********************************************************/
+//Encoder
+DigitalIn speed_yellow(p7); //yellow wire from sinusoidal encoder
+DigitalIn speed_green(p8); //green wire from sinusoidal encoder
+
+/***********************************************************/
+/*Subroutines                                              */
+/***********************************************************/
+
+//get the voltage for one of the energy storage devices. Takes pin as a parameter
+float get_voltage (AnalogIn& pin) {
+    float voltage;
+    voltage = pin.read()*3.3*(R1+R2)/R2; //scaling to account for voltage divider
+    return voltage;
+}
+
+//returns current in amps
+#ifdef CURRENT_SENSOR_ON
+void get_current() {
+    current_read = current_sense.read(); //read raw AnalogIn value of current
+    current = ISENSOR_SLOPE*current_read*3.3 + Y_INTERCEPT; //scaling to get current in A
+}
+#endif
+
+//returns speed in rad/sec
+void get_speed() {
+    current_state = speed_yellow; //get the current state of speed_yellow pin (0 or 1)
+    speed_timer.start();
+    while (speed_yellow == current_state && speed_timer <=WAIT_BEFORE_SPEEDSTOP) {} //wait for value of the speed_yellow to change, indicating the beginning of a new cycle
+    if (speed_timer < WAIT_BEFORE_SPEEDSTOP) { //check that the timer is less than WAIT_BEFORE_SPEEDSTOP, to make sure it has not been running for too long. This will happen if speed = 0
+        speed_timer.reset(); //reset the timer so that it starts timing from the beginning of the new cycle
+        begin = speed_timer.read();
+        for (int i = 1; i <= NUM_HALF_CYCLES; i++) { //loop to allow timing over a set number of encoder cycles
+            current_state = speed_yellow;
+            while (speed_yellow == current_state && speed_timer <= WAIT_BEFORE_SPEEDSTOP) {}//wait for speed_yellow pin to change. If it does not change, the loop will exit when speed_timer = WAIT_BEFORE_SPEEDSTOP
+        }
+        if (speed_timer < WAIT_BEFORE_SPEEDSTOP) {
+            end = speed_timer.read(); //time at the end of timing NUM_HALF_CYCLES cycles
+            speed_timer.stop();
+            speed =((3.14159265/8)*NUM_HALF_CYCLES)/(end-begin); //record speed in rad/sec
+        } else {
+            speed = 0; //speed = 0 if the timer has exceeded WAIT_BEFORE_SPEEDSTOP
+        }
+    } else {
+        speed = 0;  //speed = 0 if the timer has exceeded WAIT_BEFORE_SPEEDSTOP
+    }
+}
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