Callum Ellor / Mbed 2 deprecated freq_2_pins_calc

frequency calculation of incoming signal using timers

Dependencies:   USBDevice mbed

main.cpp@0:ab61f1a6b20b, 2014-11-13 (annotated)

Committer:
Ellor1
Date:
Thu Nov 13 13:23:26 2014 +0000
Revision:
0:ab61f1a6b20b
Freq_calc using timers

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Ellor1 0:ab61f1a6b20b 1 #include "mbed.h"
Ellor1 0:ab61f1a6b20b 2 #include "USBSerial.h"
Ellor1 0:ab61f1a6b20b 3
Ellor1 0:ab61f1a6b20b 4 //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
Ellor1 0:ab61f1a6b20b 5 // giving around a 3us loss in accuracy for the whole period.
Ellor1 0:ab61f1a6b20b 6 // the program starts the timer on the rising edge of the signal and stops the timer on teh falling edge. I found that
Ellor1 0:ab61f1a6b20b 7 // 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.
Ellor1 0:ab61f1a6b20b 8 // the NOT gate would liekly introduce some propagation delay but after monitoring the signal on the scope this didnt seem to be the case.
Ellor1 0:ab61f1a6b20b 9 // 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
Ellor1 0:ab61f1a6b20b 10 // decreased teh accuracy of the results as more lines of code needed to be executed.
Ellor1 0:ab61f1a6b20b 11
Ellor1 0:ab61f1a6b20b 12 USBSerial serial;
Ellor1 0:ab61f1a6b20b 13 InterruptIn int_pin(P1_14);
Ellor1 0:ab61f1a6b20b 14 InterruptIn int_pin_2(P1_24);
Ellor1 0:ab61f1a6b20b 15 Timer t1;
Ellor1 0:ab61f1a6b20b 16 Timer t2;
Ellor1 0:ab61f1a6b20b 17 Ticker display;
Ellor1 0:ab61f1a6b20b 18
Ellor1 0:ab61f1a6b20b 19 int t_period = 0; // This is the period between interrupts in microseconds
Ellor1 0:ab61f1a6b20b 20 int t_period_rise = 0;
Ellor1 0:ab61f1a6b20b 21 int t_period_fall = 0;
Ellor1 0:ab61f1a6b20b 22 int t_freq = 0;
Ellor1 0:ab61f1a6b20b 23 int results[30];
Ellor1 0:ab61f1a6b20b 24 int i =0;
Ellor1 0:ab61f1a6b20b 25 float k =0;
Ellor1 0:ab61f1a6b20b 26
Ellor1 0:ab61f1a6b20b 27 void rise()
Ellor1 0:ab61f1a6b20b 28 {
Ellor1 0:ab61f1a6b20b 29 t1.start(); // start rising edge timer
Ellor1 0:ab61f1a6b20b 30 }
Ellor1 0:ab61f1a6b20b 31
Ellor1 0:ab61f1a6b20b 32 void fall()
Ellor1 0:ab61f1a6b20b 33 {
Ellor1 0:ab61f1a6b20b 34 t1.stop(); // stop rising edge timer
Ellor1 0:ab61f1a6b20b 35 t_period_rise = t1.read_us(); // read timer in us
Ellor1 0:ab61f1a6b20b 36 t1.reset();
Ellor1 0:ab61f1a6b20b 37 }
Ellor1 0:ab61f1a6b20b 38
Ellor1 0:ab61f1a6b20b 39 void rise_2()
Ellor1 0:ab61f1a6b20b 40 {
Ellor1 0:ab61f1a6b20b 41 t2.start(); //start falling edge timer (on rising edge of pulse after inverted by NOT gate)
Ellor1 0:ab61f1a6b20b 42 }
Ellor1 0:ab61f1a6b20b 43 void fall_2()
Ellor1 0:ab61f1a6b20b 44 {
Ellor1 0:ab61f1a6b20b 45 t2.stop();
Ellor1 0:ab61f1a6b20b 46 t_period_fall = t2.read_us();
Ellor1 0:ab61f1a6b20b 47 t2.reset();
Ellor1 0:ab61f1a6b20b 48 }
Ellor1 0:ab61f1a6b20b 49
Ellor1 0:ab61f1a6b20b 50 void disp()
Ellor1 0:ab61f1a6b20b 51 {
Ellor1 0:ab61f1a6b20b 52
Ellor1 0:ab61f1a6b20b 53 // did have serial print here
Ellor1 0:ab61f1a6b20b 54
Ellor1 0:ab61f1a6b20b 55 }
Ellor1 0:ab61f1a6b20b 56
Ellor1 0:ab61f1a6b20b 57
Ellor1 0:ab61f1a6b20b 58
Ellor1 0:ab61f1a6b20b 59
Ellor1 0:ab61f1a6b20b 60
Ellor1 0:ab61f1a6b20b 61 int main() {
Ellor1 0:ab61f1a6b20b 62
Ellor1 0:ab61f1a6b20b 63
Ellor1 0:ab61f1a6b20b 64 int_pin.rise(&rise); // Set up the interrupt for rising edge
Ellor1 0:ab61f1a6b20b 65 int_pin.fall(&fall);
Ellor1 0:ab61f1a6b20b 66 int_pin_2.rise(&rise_2);
Ellor1 0:ab61f1a6b20b 67 int_pin_2.fall(&fall_2);
Ellor1 0:ab61f1a6b20b 68 //diaplay.attach(&disp, 2)
Ellor1 0:ab61f1a6b20b 69
Ellor1 0:ab61f1a6b20b 70 while (1) {
Ellor1 0:ab61f1a6b20b 71 i = ((t_period_rise) + (t_period_fall));
Ellor1 0:ab61f1a6b20b 72 k = (1/(float)i)*1000000;
Ellor1 0:ab61f1a6b20b 73 wait(3);
Ellor1 0:ab61f1a6b20b 74
Ellor1 0:ab61f1a6b20b 75 serial.printf("\rPeriod is %d \n", i);
Ellor1 0:ab61f1a6b20b 76 serial.printf("\rFrequency is %.2f \n", k);
Ellor1 0:ab61f1a6b20b 77 serial.printf("\rPeriod_rise is %d \n", t_period_rise);
Ellor1 0:ab61f1a6b20b 78 serial.printf("\rPeriod_fall is %d \n", t_period_fall);
Ellor1 0:ab61f1a6b20b 79
Ellor1 0:ab61f1a6b20b 80 }
Ellor1 0:ab61f1a6b20b 81
Ellor1 0:ab61f1a6b20b 82 }
Ellor1 0:ab61f1a6b20b 83
Ellor1 0:ab61f1a6b20b 84 //}