Diff: main.cpp

Revision:

1:0434198567a4

Parent:

0:5ed29b03d6ce

Child:

2:7a501b777146

--- a/main.cpp	Sat Aug 01 06:58:12 2015 +0000
+++ b/main.cpp	Sat Aug 01 07:51:44 2015 +0000
@@ -1,23 +1,33 @@
+/*
+** mBuino_PowerMeter
+** 
+** This program shows how to read the current voltage on the 3V3 (VCC) pin of mBuino using the blink of a LED.
+**
+** Since mBuino uses the VCC voltage as reference for analag reads, all readings are relative.
+** To get an absolute reading an external reference voltage is needed.
+** An easy way to get an external reference is by using a zener-diode with proper characteristics.
+** Not having such a zener around made me look for alternatives. I found some on this page:
+**   http://www.talkingelectronics.com/projects/200TrCcts/200TrCcts.html#52
+** The most interesting method I found was to use the LEDs on mBuino
+** See the code comments and this programs homepage for more information.
+
+**
+** 0.1.150801 First version made for mBuino on mbed.org by maxint on 1-aug-2015
+**
+** Feel free to use this code anyway you want, but please acknowledge my work by mentioning maxint as creator.
+**
+*/
+
+
 #include "mbed.h"
 #include "USBSerial.h"
 
-#define TIME_BETWEEN_SAMPLES_ms 300
-
 // The USB virtual serial port is used for debugging. Note: driver required, see http://developer.mbed.org/handbook/USBSerial
 USBSerial serialUSB(0x1f00, 0x2012, 0x0001, false); // Virtual serial port over USB, set connect_blocking to false to allow starting without PC
 #define USBSERIAL_DEBUG 1
 
 DigitalOut LED[] = {(LED1), (LED2), (LED3), (LED4), (LED5), (LED6), (LED7)};// declare 7 LEDs
 
-void ledFlash(uint8_t nLed, float ftDelay=0.005)
-{
-    if(nLed>6) nLed=6;
-    LED[nLed]=!LED[nLed];
-    wait(ftDelay);
-    LED[nLed]=!LED[nLed];
-}
-
-
 float readVCC(PinName nAnalogIn=P0_14, PinName nLed=LED6, int nBlinkDelayMsec=0, float ftVrefInit=1.91)
 {   // Unlike Arduino, mBuino v1.5 has no internal reference voltage for analog reads.
     // As all analog reads are relative to VCC, it would be nice to be able to tell the VCC
@@ -32,7 +42,7 @@
     // One way to get a reference voltage is by connecting a led via a resistor between VCC and GND.
     // The voltage over the led is (more or less) constant (about 1.7V, depending on the kind of LED).
     // This constant voltage can be measured by using a multimeter.
-    // Measured voltages are e.g. 1,77V  for a yellow led, 1,66 for a red led and 1,73 for a green led.
+    // Measured voltages are e.g. 1,77V  for a yellow led, 1,66 for a red led and 1,73 for a green led (and 1K resistor).
     // See http://www.talkingelectronics.com/projects/200TrCcts/200TrCcts.html#52 for more methods.
     //
     // As mBuino already has LEDs we can use them as a reference by connecting P0_14 to the left leg of LED7 or LED6.
@@ -57,7 +67,7 @@
 
     // Some silly trial and error compensations. Note: this compensation is not very precise!
     // TODO: improve the compensation to get more accurate readings. Now final readings may differ up to 0.10V from 
-    // actual values, depending on the reference voltage, length of the blink, VCC-level and probably temperature.
+    // actual values, depending on the reference voltage, length of the blink, resistor and LED used, VCC-level and probably temperature.
     if(!fLedStatus && nBlinkDelayMsec<=10)
         ftVref+=(0.05-nBlinkDelayMsec/200.0); //compensate for lower voltage due to short delays.
     ftVref-=(0.04+(ftVoltage-0.66)/4);   // compensation: Vref is slightly lower on low voltages.
@@ -69,18 +79,28 @@
     return(ftVoltage);
 }
 
-void SweepAllLeds(bool fLeftToRight=true, float flDelay=0.1)
+
+void ledFlash(uint8_t nLed, float ftDelay=0.005)
+{
+    if(nLed>6) nLed=6;
+    LED[nLed]=!LED[nLed];
+    wait(ftDelay);
+    LED[nLed]=!LED[nLed];
+}
+
+void SweepAllLeds(uint8_t nMaxLeds=7, bool fLeftToRight=true, float flDelay=0.1)
 {   // light all leds up from left to rigth or vise-versa and then switch them off from reverse direction
     // leds on, left to right
-    for(int n=0; n<7; n++)
+    if(nMaxLeds>7) nMaxLeds=7;
+    for(int n=0; n<nMaxLeds; n++)
     {
-        LED[fLeftToRight?n:6-n] = 1; // turn on
+        LED[fLeftToRight?n:nMaxLeds-1-n] = 1; // turn on
         wait(flDelay); // delay
     }
     // leds off, right to left
     for(int n=0; n<7; n++)
     {
-        LED[!fLeftToRight?n:6-n] = 0; // turn off
+        LED[!fLeftToRight?n:nMaxLeds-1-n] = 0; // turn off
         wait(flDelay); // delay
     }
 }
@@ -97,7 +117,7 @@
 
     // small initial delay to show all leds are working and to allow USB connection
     SweepAllLeds();
-    SweepAllLeds(false,0.02);
+    SweepAllLeds(7, false,0.02);
     SweepAllLeds();
 
     t.start();
@@ -111,7 +131,7 @@
     ledFlash(0);
     wait(0.5);
 
-    serialUSB.printf("\r\n === mBuino PowerMeter ====  \r\n");
+    serialUSB.printf("\r\n=== mBuino PowerMeter ====  \r\n");
     serialUSB.printf("Measuring LED pin %d [%1.2fV] using pin %d\r\n", pinLed, ftVled, pinAnalog);
     serialUSB.printf("Hit spacebar to change to LED pin 4 [1.85V] using pin 15.\r\n");
     while(true)
@@ -129,6 +149,7 @@
             if(ftVcc>=2.40) uLed=4;
             if(ftVcc>=2.60) uLed=5;
             if(ftVcc>=2.75) uLed=6;
+            SweepAllLeds(uLed+1);
             ledFlash(uLed);
             wait(1);
         }
@@ -143,7 +164,7 @@
             if(serialUSB._getc()==' ')
             {
                pinLed=(pinLed==P0_4?LED6:P0_4);
-               //ftVled=(ftVled!=1.85?1.85f:1.91f);
+               //ftVled=(ftVled!=1.85?1.85f:1.91f);   // hmm, weird bug; no conditional assignment on floats?
                if(ftVled!=1.91f) ftVled=1.91f; else ftVled=1.85f;
                pinAnalog=(pinAnalog==P0_15?P0_14:P0_15);
                serialUSB.printf("Switched to measuring LED pin %d [%1.2fV] using pin %d\r\n", pinLed, ftVled, pinAnalog);