Callum Ellor
frequency calculation of incoming signal using timers
Revision 0:ab61f1a6b20b, committed 2014-11-13
- Comitter:
- Ellor1
- Date:
- Thu Nov 13 13:23:26 2014 +0000
- Commit message:
- Freq_calc using timers
Changed in this revision
diff -r 000000000000 -r ab61f1a6b20b USBDevice.lib --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/USBDevice.lib Thu Nov 13 13:23:26 2014 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/USBDevice/#a4e9ddc2e2af
diff -r 000000000000 -r ab61f1a6b20b main.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Thu Nov 13 13:23:26 2014 +0000
@@ -0,0 +1,84 @@
+#include "mbed.h"
+#include "USBSerial.h"
+
+//this program uses timers to time how long the signal is high and how long the signal is low. this program manages to accurately read the signal within 1-2us on each pulsewidth
+// giving around a 3us loss in accuracy for the whole period.
+// the program starts the timer on the rising edge of the signal and stops the timer on teh falling edge. I found that
+// my readings are more accurate if i read the negative pulsewidth on a seperate pin and (int_pin_2) and I put this through a NOT gate.
+// the NOT gate would liekly introduce some propagation delay but after monitoring the signal on the scope this didnt seem to be the case.
+// Ideally if I could take a sample of the timer values and take an average my results would be better. After trying this, adding more code
+// decreased teh accuracy of the results as more lines of code needed to be executed.
+
+USBSerial serial;
+InterruptIn int_pin(P1_14);
+InterruptIn int_pin_2(P1_24);
+Timer t1;
+Timer t2;
+Ticker display;
+
+int t_period = 0; // This is the period between interrupts in microseconds
+int t_period_rise = 0;
+int t_period_fall = 0;
+int t_freq = 0;
+int results[30];
+int i =0;
+float k =0;
+
+void rise()
+{
+ t1.start(); // start rising edge timer
+ }
+
+void fall()
+{
+ t1.stop(); // stop rising edge timer
+ t_period_rise = t1.read_us(); // read timer in us
+ t1.reset();
+ }
+
+void rise_2()
+{
+ t2.start(); //start falling edge timer (on rising edge of pulse after inverted by NOT gate)
+}
+void fall_2()
+{
+ t2.stop();
+ t_period_fall = t2.read_us();
+ t2.reset();
+ }
+
+void disp()
+{
+
+ // did have serial print here
+
+ }
+
+
+
+
+
+int main() {
+
+
+ int_pin.rise(&rise); // Set up the interrupt for rising edge
+ int_pin.fall(&fall);
+ int_pin_2.rise(&rise_2);
+ int_pin_2.fall(&fall_2);
+ //diaplay.attach(&disp, 2)
+
+ while (1) {
+ i = ((t_period_rise) + (t_period_fall));
+ k = (1/(float)i)*1000000;
+ wait(3);
+
+ serial.printf("\rPeriod is %d \n", i);
+ serial.printf("\rFrequency is %.2f \n", k);
+ serial.printf("\rPeriod_rise is %d \n", t_period_rise);
+ serial.printf("\rPeriod_fall is %d \n", t_period_fall);
+
+ }
+
+}
+
+//}
diff -r 000000000000 -r ab61f1a6b20b mbed.bld --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Thu Nov 13 13:23:26 2014 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/031413cf7a89 \ No newline at end of file