Merge pull request #2 from pete-thompson/master

Add autoConfigure

ACS712.cpp

@@ -1,8 +1,8 @@
 //
 //    FILE: ACS712.cpp
-//  AUTHOR: Rob Tillaart
-// VERSION: 0.1.3
-//    DATE: 2020-03-17
+//  AUTHOR: Rob Tillaart, Pete Thompson
+// VERSION: 0.2.0
+//    DATE: 2020-08-02
 // PURPOSE: ACS712 library - current measurement
 //
 // HISTORY:
@@ -11,7 +11,7 @@
 // 0.1.2	2020-03-21 automatic formfactor test
 // 0.1.3    2020-05-27 fix library.json
 // 0.1.4    2020-08-02 Allow for faster processors
-//
+// 0.2.0    2020-08-02 Add autoMidPoint
 
 #include "ACS712.h"
 
@@ -23,7 +23,7 @@ ACS712::ACS712(uint8_t analogPin, float volts, uint16_t maxADC, uint8_t mVperA)
     _mVperAmpere = mVperA;
     _formFactor = 0.70710678119;  // 0.5 * sqrt(2);  TODO: should be smaller in practice 0.5 ?
     _midPoint = maxADC / 2;
-    _noise = 0.021 * (maxADC / volts); // Noise is 21mV according to datasheet
+    _noisemV = 21; // Noise is 21mV according to datasheet
 }
 
 int ACS712::mA_AC(uint8_t freq)
@@ -40,7 +40,7 @@ int ACS712::mA_AC(uint8_t freq)
         int val = analogRead(_pin);
         if (val < _min) _min = val;
         if (val > _max) _max = val;
-        if (abs(val - _midPoint) < _noise) zeros++;   // Noise max 4 during test
+        if (abs(val - _midPoint) <= (_noisemV/_mVpstep)) zeros++;
     }
     int p2p = (_max - _min);
 
@@ -71,4 +71,22 @@ int ACS712::mA_DC()
     return 1000.0 * steps * _mVpstep / _mVperAmpere;
 }
 
+// configure by sampling for 2 cycles of AC
+// Also works for DC as long as no current flowing
+void ACS712::autoMidPoint(uint8_t freq)
+{
+  uint32_t start = micros();
+  uint16_t twoPeriods = ((freq == 60) ? 16670 : 20000) * 2;
+  uint32_t total = 0;
+  uint32_t samples = 0;
+  while (micros() - start < twoPeriods) {
+    uint16_t reading = analogRead(_pin);
+    total += reading;
+    samples ++;
+    // Delaying ensures we won't overflow since we'll perform a maximum of 40,000 reads
+    delayMicroseconds(1);
+  }
+  _midPoint = total / samples;
+}
+
 // END OF FILE

ACS712.h

@@ -2,8 +2,8 @@
 //
 //    FILE: ACS712.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.1.3
-//    DATE: 2020-03-17
+// VERSION: 0.2.0
+//    DATE: 2020-08-02
 // PURPOSE: ACS712 library - current measurement
 //
 // Tested with a RobotDyn ACS712 20A breakout + UNO.
@@ -41,14 +41,16 @@ class ACS712
     inline uint16_t getMidPoint() { return _midPoint; };
     inline void     incMidPoint() { _midPoint++; };
     inline void     decMidPoint() { _midPoint--; };
+    // Auto midPoint, assuming zero DC current or any AC current
+    void autoMidPoint(uint8_t freq = 50);
 
     // also known as crest factor;  affects AC only
     inline void     setFormFactor(float ff) { _formFactor = ff; };
     inline float    getFormFactor() { return _formFactor; };
 
     // noise
-    inline void     setNoise(uint8_t noise) { _noise = noise; };
-    inline uint8_t  getNoise() { return _noise; };
+    inline void     setNoisemV(uint8_t noisemV) { _noisemV = noisemV; };
+    inline uint8_t  getNoisemV() { return _noisemV; };
 
     // AC and DC
     inline void     setmVperAmp(uint8_t mva) { _mVperAmpere = mva; };
@@ -60,7 +62,7 @@ class ACS712
     float     _formFactor;    // P2P -> RMS
     uint8_t   _mVperAmpere;
     uint16_t  _midPoint;
-    uint8_t   _noise;
+    uint8_t   _noisemV;
 };
 
 // END OF FILE

README.md

@@ -4,20 +4,20 @@ Current Sensor - 5A, 20A, 30A
 
 ## Description
 
-The ACS712 is a chip to measure current, both AC or DC. The chip has an 
-analog output that provides a voltage that is lineair with the current. 
+The ACS712 is a chip to measure current, both AC or DC. The chip has an
+analog output that provides a voltage that is lineair with the current.
 The ACS712 library supports only a built in ADC by means of analogRead().
 There are 2 core functions:
 
 * **int mA_DC()**
 * **int mA_AC()**
 
-To measure DC current a single analogRead() with some conversion math is sufficient to get 
+To measure DC current a single analogRead() with some conversion math is sufficient to get
 a value. To stabilize the signal analogRead() is called twice.
 
-To measure AC current **a blocking loop for 20 millis** is run to determine the 
-peak to peak value which is converted to the RMS value. To convert the peak2peak 
-value to RMS one need the so called crest or form factor. This factor depends heavily 
+To measure AC current **a blocking loop for 20 millis** is run to determine the
+peak to peak value which is converted to the RMS value. To convert the peak2peak
+value to RMS one need the so called crest or form factor. This factor depends heavily
 on the signal form. For a perfect sinus the value is sqrt(2)/2.
 
 ## Test
@@ -26,16 +26,18 @@ The library is tested with the RobotDyn ACS712 20A breakout and an Arduino UNO.
 
 ## Operation
 
-With the constructor the parameters **volts** and **maxADC (steps)** of the ADC are set 
-together with the **milliVolt per Ampere** value. The last parameter can be adjusted 
-afterwards, e.g. to callibrate this value runtime. Note this parameter affects both 
+With the constructor the parameters **volts** and **maxADC (steps)** of the ADC are set
+together with the **milliVolt per Ampere** value. The last parameter can be adjusted
+afterwards, e.g. to callibrate this value runtime. Note this parameter affects both
 AC and DC measurements.
 
-To callibrate the zero level for DC measurements, 4 functions are available to 
+To callibrate the zero level for DC measurements, 5 functions are available to
 adjust the midPoint.
 
-To callibrate the RMS value for AC measurements, 2 functions are available to 
+To callibrate the RMS value for AC measurements, 2 functions are available to
 get and set the formFactor.
 
-The examples show the basic working of the functions.
+To callibrate the noise level (used for AC measurements), 2 functions are available to
+get and set the noise in mV.
 
+The examples show the basic working of the functions.

examples/ACS712_20_AC/ACS712_20_AC.ino

@@ -15,17 +15,28 @@
 // ACS712 30A uses  66 mV per A
 
 ACS712  ACS(A0, 5.0, 1023, 100);
+// ESP 32 example (requires resistors to step down the logic voltage)
+//ACS712  ACS(25, 5.0, 4095, 185);
 
 void setup()
 {
   Serial.begin(115200);
   Serial.println(__FILE__);
+
+  ACS.autoMidPoint();
+  Serial.print("MidPoint: ");
+  Serial.print(ACS.getMidPoint());
+  Serial.print(". Noise mV: ");
+  Serial.println(ACS.getNoisemV());
 }
 
 void loop()
 {
   int mA = ACS.mA_AC();
-  Serial.println(mA);
+  Serial.print("mA: ");
+  Serial.print(mA);
+  Serial.print(". Form factor: ");
+  Serial.println(ACS.getFormFactor());
 }
 
 // END OF FILE

examples/ACS712_20_AC_DEMO/ACS712_20_AC_DEMO.ino

@@ -15,11 +15,14 @@
 // ACS712 30A uses  66 mV per A
 
 ACS712  ACS(A0, 5.0, 1023, 100);
+// ESP 32 example (requires resistors to step down the logic voltage)
+//ACS712  ACS(25, 5.0, 4095, 185);
 
 void setup()
 {
   Serial.begin(115200);
   Serial.println(__FILE__);
+  ACS.autoMidPoint();
 }
 
 void loop()

examples/ACS712_20_DC/ACS712_20_DC.ino

@@ -15,11 +15,14 @@
 // ACS712 30A uses  66 mV per A
 
 ACS712  ACS(A0, 5.0, 1023, 100);
+// ESP 32 example (requires resistors to step down the logic voltage)
+//ACS712  ACS(25, 5.0, 4095, 185);
 
 void setup()
 {
   Serial.begin(115200);
   Serial.println(__FILE__);
+  ACS.autoMidPoint();
 }
 
 void loop()

examples/ACS712_20_DC_DEMO/ACS712_20_DC_DEMO.ino

@@ -15,11 +15,14 @@
 // ACS712 30A uses  66 mV per A
 
 ACS712  ACS(A0, 5.0, 1023, 100);
+// ESP 32 example (requires resistors to step down the logic voltage)
+//ACS712  ACS(25, 5.0, 4095, 185);
 
 void setup()
 {
   Serial.begin(115200);
   Serial.println(__FILE__);
+  ACS.autoMidPoint();
 }
 
 void loop()

library.json

@@ -8,14 +8,20 @@
       "name": "Rob Tillaart",
       "email": "[email protected]",
       "maintainer": true
+    },
+    {
+      "name": "Pete Thompson",
+      "email": "[email protected]",
+      "maintainer": false
     }
+
   ],
   "repository":
   {
     "type": "git",
     "url": "https://github.com/RobTillaart/ACS712"
   },
-  "version":"0.1.3",
+  "version":"0.2.0",
   "frameworks": "arduino",
   "platforms": "*"
 }

library.properties

@@ -1,11 +1,11 @@
 name=ACS712
-version=0.1.3
-author=Rob Tillaart <[email protected]>
+version=0.2.0
+author=Rob Tillaart <[email protected]>, Pete Thompson <[email protected]>
 maintainer=Rob Tillaart <[email protected]>
-sentence=ACS712 library for Arduino. 
+sentence=ACS712 library for Arduino.
 paragraph=Current measurement, tested with RobotDyn ACDC 20A Module.
 category=Signal Input/Output
 url=https://github.com/RobTillaart/ACS712
 architectures=*
 includes=ACS712.h
-depends=
+depends=