allow custom ADC resolutions

Author: NuclearPhoenixx

PicoAnalogCorrection.cpp

@@ -6,7 +6,8 @@
 #include "PicoAnalogCorrection.h"
 
 
-PicoAnalogCorrection::PicoAnalogCorrection(int gnd_val, int vcc_val) {
+PicoAnalogCorrection::PicoAnalogCorrection(size_t adc_res, size_t gnd_val, size_t vcc_val) {
+	_max_channel = pow(2, adc_res) - 1;
 	_gnd_offset = gnd_val;
 	_vcc_offset = vcc_val;
 	setCorrectionValues();
@@ -17,7 +18,7 @@ void PicoAnalogCorrection::setCorrectionValues() {
 	if(_vcc_offset == 0) {
 		_a = 1.0;
 	} else {
-		_a = 4095.0 / (_vcc_offset - _gnd_offset);
+		_a = _max_channel / (_vcc_offset - _gnd_offset);
 	}
 	_d = - _a * _gnd_offset;
 	return;
@@ -26,19 +27,19 @@ void PicoAnalogCorrection::setCorrectionValues() {
 
 void PicoAnalogCorrection::calibrateAdc(size_t gnd_pin, size_t vcc_pin, size_t avg_size) {
 	float gnd_value = .0;
-	
+
 	for(size_t i = 0; i < avg_size; i++) {
 		gnd_value += float(analogRead(gnd_pin));
 	}
 	_gnd_offset = gnd_value/avg_size;
-	
+
 	float vcc_value = .0;
-	
+
 	for(size_t i = 0; i < avg_size; i++) {
 		vcc_value += float(analogRead(vcc_pin));
 	}
 	_vcc_offset = vcc_value/avg_size;
-	
+
 	setCorrectionValues();
 	return;
 }
@@ -53,23 +54,22 @@ void PicoAnalogCorrection::returnCalibrationValues() {
 int PicoAnalogCorrection::analogRead(size_t pin) {
 	digitalWrite(PS_PIN, HIGH); // Disable power-saving
 	delayMicroseconds(2); // Cooldown, maybe useless?
-	
+
 	int value = ::analogRead(pin); // Use normal Arduino analogRead func
-	
+
 	digitalWrite(PS_PIN, LOW); // Re-enable power-saving
-	
+
 	return value;
 }
 
 
 int PicoAnalogCorrection::analogCRead(size_t pin, size_t avg_size) {
 	float value = .0;
-	
+
 	for(size_t i = 0; i < avg_size; i++) {
-		//value += float( map(analogRead(pin), _gnd_offset, _vcc_offset, 0, 4095) );
+		//value += float( map(analogRead(pin), _gnd_offset, _vcc_offset, 0, _max_channel) );
 		value += float( _a * analogRead(pin) + _d );
 	}
-	
+
 	return round(value/avg_size);
 }
-

PicoAnalogCorrection.h

@@ -14,17 +14,17 @@
 
 class PicoAnalogCorrection {
 	private:
-		int _gnd_offset, _vcc_offset;
+		int _max_channel, _gnd_offset, _vcc_offset;
 		float _a, _d;
-		
+
 		void setCorrectionValues();
-		
+
 	public:
-		PicoAnalogCorrection(int gnd_val=0, int vcc_val=0);
-		
+		PicoAnalogCorrection(size_t adc_res=12, size_t gnd_val=0, size_t vcc_val=0);
+
 		void calibrateAdc(size_t gnd_pin, size_t vcc_pin, size_t avg_size=100);
 		void returnCalibrationValues();
-		
+
 		int analogRead(size_t pin);
 		int analogCRead(size_t pin, size_t avg_size=1);
 };

README.md

@@ -27,7 +27,7 @@ Both of these temporarily disable the power-saving mode to improve noise. Only t
 
 ## Limitations
 
-This library is limited to a very simple linear calibration since there are practically only two trusted voltages available to be measured: GND (0V) and VCC (3.3V). This means that the calibration will ensure that the ADC measures GND as 0 and VCC as 4095 with any value in between beeing distributed linearly within these two.
+This library is limited to a very simple linear calibration since there are practically only two trusted voltages available to be measured: GND (0V) and VCC (3.3V). This means that the calibration will ensure that the ADC measures GND as 0 and VCC as the maximum channel number (depending on your resolution, e.g. 4095) with any value in between being distributed linearly within these two.
 
 In addition, as the very helpful [Raspberry Pi Pico datasheet](https://datasheets.raspberrypi.com/pico/pico-datasheet.pdf) suggests, the on-board power supply noise and accuracy are not the best. To get the best results possible, you need to use an external voltage reference. This, however, introduces additonal drawbacks.
 

examples/SimpleCalibration/SimpleCalibration.ino

@@ -9,21 +9,24 @@
  * Serial Monitor. Paste them into the
  * PicoAnalogCorrection constructor and you're done.
  *
- * MIT, 2021, Phoenix1747
+ * You can also define a custom ADC resolution.
+ *
+ * MIT, 2022, Phoenix1747
  */
 
 #include <PicoAnalogCorrection.h>
 
 const uint8_t GND_PIN = A1; // GND meas pin
 const uint8_t VCC_PIN = A0; // VCC meas pin
+const uint8_t ADC_RES = 12; // ADC bits
 
-PicoAnalogCorrection pico;
+PicoAnalogCorrection pico(ADC_RES);
 
 void setup() {
   pinMode(GND_PIN, INPUT);
   pinMode(VCC_PIN, INPUT);
 
-  analogReadResolution(12); // 12-bit ADC, 4096 channels
+  analogReadResolution(ADC_RES);
 
   // Calibrate ADC using an average of 5000 measurements
   pico.calibrateAdc(GND_PIN, VCC_PIN, 5000);

library.properties

@@ -1,5 +1,5 @@
 name=PicoAnalogCorrection
-version=1.1.3
+version=1.2.0
 author=Phoenix1747
 maintainer=Phoenix1747
 sentence=Arduino library to calibrate and improve ADC measurements with the Raspberry Pi Pico.