Gerrit Pathuis / Mbed 2 deprecated Measuring_Capacitance

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Dependencies:   mbed

main.cpp@1:d95ae9068740, 2012-01-07 (annotated)

Committer:
GerritPathuis
Date:
Sat Jan 07 20:36:57 2012 +0000
Revision:
1:d95ae9068740
Parent:
0:863c3f4f452f 
Rev 2, algorithm now based on step response of a first order system.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
GerritPathuis 0:863c3f4f452f 1 #include "mbed.h"
GerritPathuis 0:863c3f4f452f 2
GerritPathuis 0:863c3f4f452f 3 //////////////////////////////////////////
GerritPathuis 0:863c3f4f452f 4 // GPa@quicknet.nl
GerritPathuis 0:863c3f4f452f 5 /////////////////////////////////////////
GerritPathuis 0:863c3f4f452f 6 //
GerritPathuis 1:d95ae9068740 7 // An unkwown ceramic capacitor is connected to
GerritPathuis 1:d95ae9068740 8 // pin21 via a 82 kilo ohm resister, the other
GerritPathuis 0:863c3f4f452f 9 // capacitor terminal is connected to ground
GerritPathuis 0:863c3f4f452f 10 //
GerritPathuis 1:d95ae9068740 11 // A ceramic capacitor is used becouse it is non polarized
GerritPathuis 1:d95ae9068740 12 //
GerritPathuis 0:863c3f4f452f 13 // ||
GerritPathuis 1:d95ae9068740 14 // pin21-----RRRRRRR-----------||------- pin1 (GND)
GerritPathuis 1:d95ae9068740 15 // | ||
GerritPathuis 0:863c3f4f452f 16 // 82k ohm | ?? Farad
GerritPathuis 0:863c3f4f452f 17 // |
GerritPathuis 0:863c3f4f452f 18 // pin20-------------------
GerritPathuis 0:863c3f4f452f 19 //
GerritPathuis 0:863c3f4f452f 20 // Mbed pins used
GerritPathuis 0:863c3f4f452f 21 // Pin 20...... analog input
GerritPathuis 0:863c3f4f452f 22 // Pin 21...... digital out
GerritPathuis 0:863c3f4f452f 23 //////////////////////////////////////////
GerritPathuis 0:863c3f4f452f 24 // How does it work
GerritPathuis 0:863c3f4f452f 25 // measure voltage on pin 20
GerritPathuis 0:863c3f4f452f 26 // If (not zero Volt) then wait
GerritPathuis 0:863c3f4f452f 27 // else pin 21 goes high 3.3 Volt
GerritPathuis 1:d95ae9068740 28 // Capacitor is charging
GerritPathuis 1:d95ae9068740 29 // wait until 3.13 Volt being 3 Tou
GerritPathuis 1:d95ae9068740 30 // Theory step response on a first order system
GerritPathuis 0:863c3f4f452f 31 //
GerritPathuis 1:d95ae9068740 32 // 1 x Tou= 63% final value
GerritPathuis 1:d95ae9068740 33 // 2 x Tou= 86% final value
GerritPathuis 1:d95ae9068740 34 // 3 x Tou= 95% final value
GerritPathuis 1:d95ae9068740 35 //
GerritPathuis 1:d95ae9068740 36 // Tou = R x C
GerritPathuis 1:d95ae9068740 37 // ==> C = Tou / R
GerritPathuis 0:863c3f4f452f 38 //
GerritPathuis 0:863c3f4f452f 39 // The measuring results are send via Teraterm to the PC screen
GerritPathuis 0:863c3f4f452f 40 // Note 1)
GerritPathuis 0:863c3f4f452f 41 // The tolerance range of a ceramic capacitor
GerritPathuis 0:863c3f4f452f 42 // lies between 5 and 100%, not very accure at all.
GerritPathuis 0:863c3f4f452f 43 // Note 2)
GerritPathuis 0:863c3f4f452f 44 //
GerritPathuis 0:863c3f4f452f 45 // Cap sizes are
GerritPathuis 0:863c3f4f452f 46 // m = 10^-3 (mili)
GerritPathuis 0:863c3f4f452f 47 // u = 10^-6 (micro)
GerritPathuis 0:863c3f4f452f 48 // n = 10^-9 (nano)
GerritPathuis 0:863c3f4f452f 49 // p = 10^-12 (pico)
GerritPathuis 0:863c3f4f452f 50 // f = 10^-15 (femto)
GerritPathuis 0:863c3f4f452f 51 /////////////////////////////////////////
GerritPathuis 0:863c3f4f452f 52
GerritPathuis 0:863c3f4f452f 53 AnalogIn ain(p20);
GerritPathuis 0:863c3f4f452f 54 DigitalOut red(p21);
GerritPathuis 0:863c3f4f452f 55 Serial pc(USBTX, USBRX); // tx, rx
GerritPathuis 1:d95ae9068740 56 Timer timer;
GerritPathuis 0:863c3f4f452f 57
GerritPathuis 0:863c3f4f452f 58 int main() {
GerritPathuis 1:d95ae9068740 59 int i;
GerritPathuis 1:d95ae9068740 60 double timec;
GerritPathuis 1:d95ae9068740 61 double volt; // Voltage measurement
GerritPathuis 1:d95ae9068740 62 double cx; // capacitance
GerritPathuis 0:863c3f4f452f 63
GerritPathuis 0:863c3f4f452f 64 pc.baud(9600);
GerritPathuis 0:863c3f4f452f 65 pc.format(8,Serial::None,1);
GerritPathuis 0:863c3f4f452f 66
GerritPathuis 0:863c3f4f452f 67 for (i=0; i<2250; i +=1) {
GerritPathuis 1:d95ae9068740 68 wait_ms(10); // deterime the number of measurements
GerritPathuis 0:863c3f4f452f 69
GerritPathuis 1:d95ae9068740 70 // Wait for 0.0 volt on input
GerritPathuis 1:d95ae9068740 71 red.write(0);
GerritPathuis 1:d95ae9068740 72 volt = 1;
GerritPathuis 1:d95ae9068740 73 while (volt > 0.0001) { // wait for 0.0 Volt
GerritPathuis 1:d95ae9068740 74 wait_us(2);
GerritPathuis 1:d95ae9068740 75 volt = ain.read();
GerritPathuis 0:863c3f4f452f 76 }
GerritPathuis 1:d95ae9068740 77 // start to measure
GerritPathuis 1:d95ae9068740 78 timer.reset();
GerritPathuis 1:d95ae9068740 79 timer.start();
GerritPathuis 0:863c3f4f452f 80 red.write(1); // output high
GerritPathuis 1:d95ae9068740 81
GerritPathuis 1:d95ae9068740 82 while (volt < 3.13) { // wait for 3.13 Volt
GerritPathuis 1:d95ae9068740 83 volt = ain.read()*3.3;
GerritPathuis 1:d95ae9068740 84 }
GerritPathuis 1:d95ae9068740 85 timer.stop();
GerritPathuis 1:d95ae9068740 86 timec=timer.read();
GerritPathuis 0:863c3f4f452f 87 red.write(0); // output low
GerritPathuis 0:863c3f4f452f 88
GerritPathuis 0:863c3f4f452f 89 // calculations
GerritPathuis 1:d95ae9068740 90 cx = (double) timec/ (3 * 82000);
GerritPathuis 0:863c3f4f452f 91
GerritPathuis 1:d95ae9068740 92 pc.printf("Volt %3.2f, time %9.4f msec ", volt, timec*1000);
GerritPathuis 1:d95ae9068740 93 if (cx < 1 and cx >= 0.001) {
GerritPathuis 1:d95ae9068740 94 cx = cx *1000;
GerritPathuis 1:d95ae9068740 95 pc.printf("Cap. is %5.1f milli Farad ", cx);
GerritPathuis 1:d95ae9068740 96 } else if (cx < 0.001 and cx >= 0.000001) {
GerritPathuis 1:d95ae9068740 97 cx = cx *1000 *1000;
GerritPathuis 1:d95ae9068740 98 pc.printf("Cap. is %5.1f micro Farad ", cx);
GerritPathuis 1:d95ae9068740 99 } else if (cx < 0.000001 and cx >= 0.000000001) {
GerritPathuis 1:d95ae9068740 100 cx = cx *1000 *1000 *1000;
GerritPathuis 1:d95ae9068740 101 pc.printf("Cap. is %5.1f nano Farad ", cx);
GerritPathuis 1:d95ae9068740 102 } else if (cx < 0.000000001 and cx >= 0.000000000001) {
GerritPathuis 1:d95ae9068740 103 cx = cx *1000 *1000 *1000 *1000;
GerritPathuis 1:d95ae9068740 104 pc.printf("Cap. is %5.1f pico Farad ", cx);
GerritPathuis 1:d95ae9068740 105 } else if (cx < 0.000000000001)
GerritPathuis 1:d95ae9068740 106 pc.printf("Cx = %5.1f Out of range too small! ", cx);
GerritPathuis 1:d95ae9068740 107 pc.printf("\r");
GerritPathuis 1:d95ae9068740 108 pc.printf("\n");
GerritPathuis 0:863c3f4f452f 109 }
GerritPathuis 1:d95ae9068740 110 }