Revision 0:da6189dcf7e6, committed 2014-01-08

Comitter:

kuldipmaharjan

Date:

Wed Jan 08 00:35:21 2014 +0000

Commit message:

I used this code to try to make a capacitance reader using mbed; It contains tweaked version of others' code so not all credit goes to me;

Changed in this revision

diff -r 000000000000 -r da6189dcf7e6 main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Jan 08 00:35:21 2014 +0000
@@ -0,0 +1,116 @@
+//Author: Kuldip Maharjan
+//Email : kuldipmaharjan@gmail.com
+//Anyone can use this code if it helps in their projects or 
+//for learning programing in mbed besides for commercial purposes
+
+
+//I used this code to try to make a capacitance reader using mbed
+//It contains tweaked version of others' code so not all credit goes to me
+
+#include "mbed.h"
+ 
+//
+// An unkwown ceramic capacitor is connected to
+// pin21 via a 82 kilo ohm resister, the other
+// capacitor terminal is connected to ground
+//
+// A ceramic capacitor is used becouse it is non polarized
+//
+//                                 ||
+//     pin21-----RRRRRRR-----------||------- pin1 (GND)
+//                            |    ||
+//                82k ohm     |    ?? Farad
+//                            |
+//     pin20-------------------
+//
+// Mbed pins used
+// Pin 20...... analog input
+// Pin 21...... digital out
+//////////////////////////////////////////
+// How does it work
+// measure voltage on pin 20
+// If (not zero Volt) then wait
+// else pin 21 goes high 3.3 Volt
+// Capacitor is charging
+// wait until 3.13 Volt being 3 Tou
+// Theory step response on a first order system
+//
+// 1 x Tou= 63% final value
+// 2 x Tou= 86% final value
+// 3 x Tou= 95% final value
+//
+// Tou = R x C
+// ==> C = Tou / R
+//
+// The measuring results are send via Teraterm to the PC screen
+// Note 1)
+// The tolerance range of a ceramic capacitor
+// lies between 5 and 100%, not very accure at all.
+// Note 2)
+//
+// Cap sizes are
+// m = 10^-3  (mili)
+// u = 10^-6  (micro)
+// n = 10^-9  (nano)
+// p = 10^-12 (pico)
+// f = 10^-15 (femto)
+/////////////////////////////////////////
+ 
+AnalogIn ain(p20);
+DigitalOut red(p21);
+Serial pc(USBTX, USBRX); // tx, rx
+Timer timer;
+ 
+int main() {
+    int i;
+    double timec;
+    double volt;       // Voltage measurement
+    double cx;         // capacitance
+ 
+    pc.baud(9600);
+    pc.format(8,Serial::None,1);
+ 
+    for (i=0; i<2250; i +=1)  {
+        wait_ms(100);                  // deterime the number of measurements
+ 
+        // Wait for 0.0 volt on input
+        red.write(0);
+        volt = 1;
+        while (volt > 0.0001) {     // wait for 0.0 Volt
+            wait_us(2);
+            volt = ain.read();
+        }
+        // start to measure
+        timer.reset();
+        timer.start();
+        red.write(1);               // output high
+ 
+        while (volt < 3.13) {       // wait for 3.13 Volt
+            volt = ain.read()*3.3;
+        }
+        timer.stop();
+        timec=timer.read();
+        red.write(0);               // output low
+ 
+        // calculations
+        cx = (double) timec/ (3 * 82000);
+ 
+        pc.printf("Volt %3.2f, time %9.4f msec ", volt, timec*1000);
+        if (cx < 1 and cx >= 0.001) {
+            cx = cx *1000;
+            pc.printf("Cap. is %5.1f milli Farad    ", cx);
+        } else if (cx < 0.001 and cx >= 0.000001) {
+            cx = cx *1000 *1000;
+            pc.printf("Cap. is %5.1f micro Farad     ", cx);
+        } else if (cx < 0.000001 and cx >= 0.000000001) {
+            cx = cx *1000 *1000 *1000;
+            pc.printf("Cap. is %5.1f nano Farad      ", cx);
+        } else if (cx <  0.000000001 and cx >=  0.000000000001) {
+            cx = cx *1000 *1000 *1000 *1000;
+            pc.printf("Cap. is %5.1f pico Farad       ", cx);
+        } else if (cx < 0.000000000001)
+            pc.printf("Cx = %5.1f Out of range too small! ", cx);
+        pc.printf("\r");
+        pc.printf("\n");
+    }
+}
\ No newline at end of file

diff -r 000000000000 -r da6189dcf7e6 mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Wed Jan 08 00:35:21 2014 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/5e5da4a5990b
\ No newline at end of file