oscillatorAVR.ino

examples/oscillatorAVR/oscillatorAVR.ino

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+/***************************************************
+  This is an example for our Adafruit 16-channel PWM & Servo driver
+  to calibrate the frequency of the oscillator clock of the PCA9685.
+
+  Connect the PCA9685 with I2C (Ground, VCC, SCL, SCA) and apply
+  voltage on V+. See above not higher than board limits.
+  Connect the signal (yellow pin, PWM) of the PCA9685 to your board:
+  Default is pin 3, last of first block.
+  Default is pin 2 (of your Arduino Uno).
+
+  Formula for prescale to get the targetted frequency (=update_rate) is:
+  prescale = round ( osc_clock / 4096 * update_rate) - 1
+  rewritten: osc_clock = (prescale + 1) * 4096 * update_rate
+  We will measure the real update_rate to assert the real osc_clock.
+
+https://forum.arduino.cc/t/servo-frequency/984914/18
+
+Working frequency: 50-330Hz
+
+hm 330 Hz means a timeperiod of 1/ 330 = 0.00303 seconds
+This means each 3 milliseconds a 2 milliseconds pulse is created
+hm well this fits into a a 3 milliseconds interval.
+
+The turning speed at 6.8V is 0.12sec / 60 = 0.002 seconds per degree
+this means correction of 1 or 2 degrees could be achieved physically withing the 3 millisecond-period of a 330 Hz signal.
+
+a turn of 90 degrees needs 0.12 / 60 * 90 = 0.24 seconds
+
+With a 50 Hz signal wich is a timeperiod of 1/50 = 0.02 seconds
+a 0.02 / 0.003 = 6.67 degree is done.
+This means only in case of angles smaller than 6.67 degree there is an advantage of a signal-frequency bigger than the standard 50 Hz.
+
+I have doubts if this is nescessary for your robot. Depending on your mechanic high-speed moving can (but must not) cause unwanted oscillations of the robots mechanical components.
+
+  ***************************************************/
+
+#include <Wire.h>
+#include <Adafruit_PWMServoDriver.h>
+
+// called this way, it uses the default address 0x40
+Adafruit_PWMServoDriver PCA9685 = Adafruit_PWMServoDriver(0x40, Wire);
+// you can also call it with a different address you want
+//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x40);
+// you can also call it with a different address and I2C interface
+//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x40, Wire);
+
+// Applied frequency in the test: can be changed to get the optimal
+// oscillator calibration for your targetted frequency.
+#define FREQUENCY 70
+
+#define PIN_SERVO_FEEDBACK 3 // Connect Yellow PWM pin, 3 = last on first block
+#define PIN_BOARD_FEEDBACK 2 // 2 => D2
+
+uint8_t prescale = 0;
+// loop
+#define INTERVAL 1000000  // 1 sec
+int32_t lastEvaluation = 0;
+uint16_t frozenCounter = 0;
+
+uint32_t totalCounter = 0;
+uint32_t totalTime = 0; // in millis
+uint32_t realOsciFreq = 0;
+uint64_t Sum_realOsciFreq = 0;
+uint32_t Average_realOsciFreq = 0;
+uint32_t multiplier = 4096;
+
+// interrupt
+volatile uint16_t interruptCounter = 0;
+
+void Update_INT_ISR()
+{
+	interruptCounter++;
+}
+
+void setup()
+{
+	Serial.begin(115200);
+	Serial.println(" PCA9685 Oscillator test");
+
+	// set PCA9685
+	PCA9685.begin();
+	PCA9685.setPWMFreq(FREQUENCY);             // Set some frequency
+	PCA9685.setPWM(PIN_SERVO_FEEDBACK,0,2048); // half of time high, half of time low
+	prescale = PCA9685.readPrescale();         // read prescale
+	Serial.print(" Target frequency: ");
+	Serial.println(FREQUENCY);
+	Serial.print(" Applied prescale: ");
+	Serial.println(prescale);
+
+	// prepare interrupt pin
+	pinMode(PIN_BOARD_FEEDBACK, INPUT);
+	attachInterrupt(digitalPinToInterrupt(PIN_BOARD_FEEDBACK), Update_INT_ISR, RISING);
+
+	// take a breath and reset to zero
+	delay(10);
+	interruptCounter = 0;
+	lastEvaluation = micros();
+}
+
+void loop()
+{
+	if (micros() - lastEvaluation > INTERVAL)
+	{
+		// first freeze counters and adjust for new round
+		frozenCounter = interruptCounter; // first freeze counter
+		interruptCounter -= frozenCounter;
+		lastEvaluation += INTERVAL;
+
+		totalCounter += frozenCounter;
+		totalTime += 1;
+
+		// only print deviations from targetted frequency
+		//if (frozenCounter != FREQUENCY)
+		{
+			multiplier = 4096;
+			realOsciFreq = (prescale + 1) * totalCounter; // first part calcutlation
+			// now follows an ugly hack to have maximum precision in 32 bits
+			while (((realOsciFreq & 0x80000000) == 0) && (multiplier != 1))
+			{
+				realOsciFreq <<= 1;
+				multiplier >>= 1;
+			}
+			realOsciFreq /= totalTime;
+			if (multiplier) realOsciFreq *= multiplier;
+
+			Sum_realOsciFreq = Sum_realOsciFreq + realOsciFreq;
+			Average_realOsciFreq = Sum_realOsciFreq/totalTime;
+
+			Serial.print(" Timestamp: ");
+			Serial.println(totalTime);
+			Serial.print(" Freq: ");
+			Serial.println(frozenCounter);
+			Serial.print(" Counter: ");
+			Serial.println(totalCounter);
+			Serial.print(" calc.osci.freq: ");
+			Serial.println(realOsciFreq);
+			Serial.print(" Average_realOsciFreq: ");
+			Serial.println(Average_realOsciFreq);
+		}
+	}
+}