version 2

Author: gavinlyonsrepo

Cap_meter_arduino/Cap_meter_arduino.ino

@@ -24,21 +24,20 @@ Adafruit_SSD1306 display(OLED_RESET);
 #define analogPin      6
 #define chargePin      12
 #define dischargePin   11
-#define resistorValue  10000.0F
+#define resistorValue  9988.0F // 10K in theory User adjust
 
 
 // Pins and vars for test 2
-const int OUT_PIN = A3;  // pos pin
-const int IN_PIN = A2;
-const float IN_STRAY_CAP_TO_GND = 24.48;
-const float IN_CAP_TO_GND  = IN_STRAY_CAP_TO_GND;
-const float R_PULLUP = 34.8;
-const int MAX_ADC_VALUE = 1023;
+const int OutPin = A3; 
+const int InPin = A2;
+const float CapOne = 24.48; //user calibrate
+const float Res_Pullup = 34.8;
+const int MaxADC_Value = 1023;
 
 
 //Pins and vars for test 3
 const byte pulsePin = 2;
-const unsigned long resistance = 9830; // (10K in theory)
+const unsigned long resistance = 9830; // (10K in theory) user adjust
 volatile boolean triggered;
 volatile boolean active;
 volatile unsigned long startTime;
@@ -65,6 +64,12 @@ int test_count = 0;
 //*************************** SETUP ************************
 void setup() {
 
+   // Status LED
+   pinMode(LED_BUILTIN, OUTPUT);
+   digitalWrite(LED_BUILTIN, HIGH);  
+   delay(80);                    
+   digitalWrite(LED_BUILTIN, LOW);
+   
   // Setup pins for button enable internal pull-up resistors
   digitalWrite(3, HIGH);
   digitalWrite(8, HIGH);
@@ -73,15 +78,22 @@ void setup() {
   btn_test_two.begin();
   btn_test_three.begin();
 
-  // Setup pins for testing 1 and 2
+  // Setup pins for test 1
   pinMode(chargePin, OUTPUT);
-  pinMode(OUT_PIN, OUTPUT);
-  pinMode(IN_PIN, OUTPUT);
   digitalWrite(chargePin, LOW);
-  //test3
+   
+  // Setup pins for test 2
+  pinMode(OutPin, OUTPUT);
+  pinMode(InPin, OUTPUT);
+  
+  // setup for test3
   pinMode(pulsePin, OUTPUT);
   digitalWrite(pulsePin, LOW);
-  ADCSRB = 0;
+  // Set up Analog Comparator
+  ADCSRB = 0; // clear ADCSRB registers
+  // Analog Comparator Interrupt Flag: Clear Pending Interrupt 
+  // Analog Comparator Interrupt: Enabled 
+  // Analog Comparator Interrupt Mode: interrupt on the rising edge
   ACSR =  _BV (ACI)
           | _BV (ACIE)
           | _BV (ACIS0) | _BV (ACIS1);
@@ -91,7 +103,6 @@ void setup() {
   //display intial OLED screen
   Display_init();
   Serial.println("------------- CAP Meter Comms UP ------------");
-  delay(500);
 }
 
 //******************* MAIN LOOP *****************
@@ -113,7 +124,6 @@ void loop() {
   }
 }
 
-
 // ********************* FUNCTIONS *************************
 
 //Function to handle test1
@@ -168,16 +178,16 @@ void Test_two()
   display.clearDisplay();
   display.setCursor(0, 0);
 
-  pinMode(IN_PIN, INPUT);
-  digitalWrite(OUT_PIN, HIGH);
-  int val = analogRead(IN_PIN);
-  digitalWrite(OUT_PIN, LOW);
+  pinMode(InPin, INPUT);
+  digitalWrite(OutPin, HIGH);
+  int val = analogRead(InPin);
+  digitalWrite(OutPin, LOW);
 
   if (val < 1000)
   {
-    pinMode(IN_PIN, OUTPUT);
+    pinMode(InPin, OUTPUT);
     // Cu = VA2 * C1 / (VA3 - VA2)
-    float capacitance = (float)val * IN_CAP_TO_GND / (float)(MAX_ADC_VALUE - val);
+    float capacitance = (float)val * CapOne / (float)(MaxADC_Value - val);
     Serial.print(F("Capacitance Value = "));
     Serial.print(capacitance, 3);
     Serial.print(F(" pF ("));
@@ -188,33 +198,33 @@ void Test_two()
   }
   else
   {
-    pinMode(IN_PIN, OUTPUT);
+    pinMode(InPin, OUTPUT);
     delay(1);
-    pinMode(OUT_PIN, INPUT_PULLUP);
+    pinMode(OutPin, INPUT_PULLUP);
     unsigned long u1 = micros();
     unsigned long t;
     int digVal;
     do
     {
-      digVal = digitalRead(OUT_PIN);
+      digVal = digitalRead(OutPin);
       unsigned long u2 = micros();
       // condition ? result_if_true : result_if_false
       t = u2 > u1 ? u2 - u1 : u1 - u2;
     } while ((digVal < 1) && (t < 400000L));
 
-    pinMode(OUT_PIN, INPUT);
-    val = analogRead(OUT_PIN);
+    pinMode(OutPin, INPUT);
+    val = analogRead(OutPin);
 
     //discharge
-    digitalWrite(IN_PIN, HIGH);
+    digitalWrite(InPin, HIGH);
     int dischargeTime = (int)(t / 1000L) * 5;
     delay(dischargeTime);
-    pinMode(OUT_PIN, OUTPUT);
-    digitalWrite(OUT_PIN, LOW);
-    digitalWrite(IN_PIN, LOW);
+    pinMode(OutPin, OUTPUT);
+    digitalWrite(OutPin, LOW);
+    digitalWrite(InPin, LOW);
 
-    float capacitance = -(float)t / R_PULLUP
-                        / log(1.0 - (float)val / (float)MAX_ADC_VALUE);
+    float capacitance = -(float)t / Res_Pullup
+                        / log(1.0 - (float)val / (float)MaxADC_Value);
     Serial.print(F("Capacitance Value = "));
     if (capacitance > 1000.0)
     {
@@ -297,10 +307,12 @@ void Test_three(void)
   }
 }
 
-// Function to handle button press start display to OLED and serial Mon
+// Function to handle button press start display to OLED and serial monitor
 void TestButton(int which_button)
 {
+  digitalWrite(LED_BUILTIN, LOW);
   test_count ++;
+  
   Serial.print("testcount: ");
   Serial.println(test_count);
   Serial.print("Buttonpressed: ");
@@ -359,15 +371,15 @@ void Display_init()
   display.clearDisplay();
 
   display.setCursor(0, 0);
-  display.print("Test 2 center");
+  display.print("Test 2 left");
   display.setCursor(0, 15);
   display.print("Range 18pF - 470uF");
   display.display();
   delay(1500);
   display.clearDisplay();
 
   display.setCursor(0, 0);
-  display.print("Test 3 Left");
+  display.print("Test 3 top");
   display.setCursor(0, 15);
   display.print("Range 4.7nF - 180uF");
   display.display();
@@ -377,14 +389,15 @@ void Display_init()
 
 }
 
-//Function to display ready message
+//Function to display ready message and Status LED
 void OLEDready()
-{
+{ 
   display.clearDisplay();
   display.setTextSize(2);
   display.setCursor(0, 0);
   display.print("Ready");
   display.display();
+  digitalWrite(LED_BUILTIN, HIGH);
 }
 
 //******************* EOF *****************

README.md

@@ -3,7 +3,7 @@ Overview
 * Name : Cap_meter_arduino
 * Title : Capacitance meter Arduino based microcontroller.
 * Description : Capacitance meter for Arduino, three tests , 
-range 18pf to 4F , Push Button input , OLED and serial monitor output.
+range 18pf to 4F , Push Button input , OLED, serial monitor output and LED(onboard NANO)
 * Author: Gavin Lyons
 * URL: https://github.com/gavinlyonsrepo/Cap_meter_arduino
 
@@ -32,9 +32,9 @@ You will need following parts
 
 > Three pushbuttons
 >
-> Resistors Test2(10Kohm and 220ohm) , Test3(10K, 3.1K 1.8K)
+> Resistors: Test2(10Kohm and 220ohm) , Test3(10K, 3.1K, 1.8K)
 >
-> Arduino micro-controller (tested on a NANO and UNO)
+> Arduino NANO micro-controller module (tested on a NANO and UNO)
 >
 > I2C 0.91" inch 128x32 OLED Display Module SSD1306 Driver IC
 >
@@ -50,7 +50,12 @@ Three push buttons start the three tests respectively.
 
 1. Test 1 Range  1 uF to 4F.
 2. Test 2 Range 18 pF to 470 uF.
-3. Test 3 Range 0.0047 uF to 180 uF.
+3. Test 3 Range 4.7 nF to 180 uF.
+
+The on-board LED of nano module D13 is used as Status LED.
+It Flashes during startup, stays on during "READY to test" state and goes off during "TESTING" state
+
+The OLED displays  brief help message and title screen duirng start-up
 
 Each Arduino capacitance meter relies on a property of resistor capacitor (RC) circuits- the time constant. 
 The time constant of an RC circuit is defined as the time it takes for the voltage across the capacitor 
@@ -73,35 +78,45 @@ we can use the formula above in a program that will calculate the unknown capaci
 
 Test 1: Range  1 uF to 4F. 
 Uses two digital pins, one analog pin, and two resistors.
-One for discharge one for charge
-Insert a capacitor in range into terminal press button and view result on OLED or serial monitor
-The result gives two values: value of cap in uF and time constant to test in mS.
+One for discharge, one for charge.
+Insert a capacitor in range into terminal press button and view result on OLED or serial monitor.
+The Capacitor is charged,  We can measure elapsed time until time constant fulfilled using analog pin and we know R 
+value. Therefore we solve for C. 
+The result gives two values: Capacitance value and time constant to test in mS.
+The user can adjust the 10K resistor value in code variable(resistorValue) to match exact value, to improve accuracy
 
 ![ScreenShot cap sch](https://github.com/gavinlyonsrepo/Cap_meter_arduino/blob/master/images/sch.jpg)
 
 **Test 2**
 
 Test 2 : Range 18 pF to 470 uF.
+
 This capacitance test has the greatest range of two. It also had the highest accuracy with smaller capacitors. 
 No resistors are needed and it only uses two analog pins(A2(neg) and A3(positive) from the Arduino.
 There is no extra resistor just the internal components of atmega chip.
+
+C1 calibration(optional): 
+
 The internal analog pin capacitor to gnd (C1) varies between 20 and 30pF. unknown capacitor = Cu.
 The positive pin is set to 5V, the negative to 0V.
-VA2 = (VA3*Cu)/(C1 + Cu).
+VA2 = (VA3 * Cu)/(C1 + Cu).
+The value of C1 for any given Arduino board will have to be calibrated using a known cap for Cu,
+for full accuracy I set it at 24.48pF in code (CapOne) Found using equation.
+C1 = Cu * (VA3-VA2) / VA3, Where  Va2 is ADC value reported by code and VA3 is 5v or 1023.
+So for a known capacitor of 103pF giving a ADC value of 801.
+So C1 = 103pf * (1023-801)/ 1023 = 28.48pF.
+The user should change this for their system to improve accuracy.
+Test a known cap get ADC value and then pop these values into equation above
+and put the C1 value into (CapOne) variable in code.
 
-The value of C1 for any given Arduino board will have to be calibrated using a known cap for Cu
-for full accuracy I set it at 24.48pF in code(IN_STRAY_CAP_TO_GND) Found using equation.
-C1 = Cu *(VA3-VA2) / VA3, Where  Va2 is ADC value reported by code and VA3 is 5v or 1023.
-so for a known capacitor of 103pF giving a ADC value of 801
-so C1 = 102pf * (1023-801)/ 1023 = 28.48pF.
-The user will have to change IN_STRAY_CAP_TO_GND for their system.
+Test equation:
+
+Cu = VA2 * C1 / (VA3 - VA2)
 
-Test a known cap get ADC value and then pop these values into equation above
-and put the C1 value into IN_STRAY_CAP_TO_GND  variable in code.
 The test displays 3 values 
-* Capacitance in Farads
+* Cu,  Capacitance in Farads 
 * Time constant for test in mS
-* ADC measurement from 0 to 1023 where 1023 is 5V
+* Va2 , ADC measurement from 0 to 1023 where 1023 is 5V 
 
 ![ScreenShot cap sch 2](https://github.com/gavinlyonsrepo/Cap_meter_arduino/blob/master/images/test2sch.jpg)
 
@@ -113,14 +128,23 @@ Test 3 Range 0.0047 uF to 180 uF.
 ![ScreenShot cap sch 3](https://github.com/gavinlyonsrepo/Cap_meter_arduino/blob/master/images/test3sch.jpg)
 
 A voltage divider is created to give a reference voltage,
+
 Vout = Vin * (R5 / (R5 + R4)) , 5 * (3100 / (1800 + 3100)) = 3.163.
+
 The objective here is to find the time constant τ (tau) in the equation:
+
 τ = R * C Solved for C: C = τ / R
+
 So we want to charge the capacitor under test with a suitable voltage (eg. 5V from an Arduino output pin) and measure how long it takes to reach 63.2% of that voltage. So we need a reference voltage of 5 * 0.632, namely 3.16V.
-The internal analogue comparator is just the thing for the job. We connect the reference voltage to the AIN1 pin (negative reference) and connect our capacitor to the AIN0 pin (positive reference) and then configure an interrupt on the rising edge. A value of 10K for the resistor to give a reasonably slow charge time. The value of 10K is specified in code
-so adjust for your resistor I have 9830 ohms, and make sure to pick accurate resistors for voltage divider.
+The internal analogue comparator is used for this job.:
+
+1. pin 6 PD6 AIN0
+2. pin 7 PD7 AIN1
+ 
+We connect the reference voltage to the AIN1 pin (negative reference) and connect our capacitor to the AIN0 pin (positive reference) and then configure an interrupt on the rising edge. A value of 10K for the resistor to give a reasonably slow charge time. The value of ~ 10K is specified in code variable (resistance).
+so adjust for your resistor value , I have 9830 ohms. Make sure to pick accurate resistors for voltage divider.
 
-The test returns the Capacitance in nF and time constant.
+The test returns the Capacitance result and time constant.
 
 Project Schematic 
 ----------------------------

docs/CHANGELOG.md

@@ -3,12 +3,8 @@
 * version 1.0-1 May 2018 
 	first release
 
-* version 1.1-2 October 2018
-	added help information to init screen
-
-* version 2.0-1 December 2018
-	Added third test, third button.
-
-* Version  2.1-2 Feb  2019
-	1. Improved and Optimized various displays and test results on the OLED screen.
-	2. Removed Adafruit OLED graphic library declaration and defines from code, was never used since testing.
+* version 2.0-1 Feb 2019
+ 	1. Added third test, third button.
+	2. Improved and Optimized the information display on the OLED 
+	3. Status LED implented using nano onboard
+	4. documentation and schematics improvements