PIC32MX: Sinusoidal Analog Output - Revision history

LawrenceChen: /* Frequency */

2010-05-31T03:21:40Z

Frequency

LawrenceChen: /* Sample Code */

2010-05-31T03:14:53Z

Sample Code

LawrenceChen: /* Frequency */

2010-05-31T03:13:30Z

Frequency

LawrenceChen: /* Frequency */

2010-05-31T03:05:53Z

Frequency

LawrenceChen: /* Frequency */

2010-05-31T03:03:37Z

Frequency

LawrenceChen: /* Frequency */

2010-05-31T03:00:14Z

Frequency

LawrenceChen: /* Frequency */

2010-05-31T02:54:25Z

Frequency

LawrenceChen: /* Frequency */

2010-05-31T02:54:09Z

Frequency

Andrew Long at 13:57, 21 May 2010

2010-05-21T13:57:58Z

Andrew Long at 13:56, 21 May 2010

2010-05-21T13:56:19Z

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 [[Image:20HzRC4-7.jpg|center|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 20Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
+[[Image:Pk2PkVSFreq.jpg|center|frame|Graph of the results from an experiment. This experiment had a cutoff frequency of 33Hz (47kOhm resistor; 0.1 microFarad capacitor). If the sine frequency is too low relative to the cutoff frequency, the amplitude of the voltage may be smaller than the maximum output. If the sine frequency is too high relative to the cutoff frequency, the amplitude of the voltage also decreases. Thus it is ideal to pick a frequency that's in the middle ground, if possible.]]
 ==Sample Code==

← Older revision		Revision as of 03:14, 31 May 2010
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	[[Image:20HzRC4-7.jpg\|center\|frame\|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 20Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]		[[Image:20HzRC4-7.jpg\|center\|frame\|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 20Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]


	==Sample Code==		==Sample Code==

@@ Line 48: / Line 48: @@
 This cut-off frequency can cause a loss in the output amplitude. The determination of if the cut-off frequency is too high depends on the sine frequency. If the cut-off frequency is too high (RC constant is too low) relative to the sine frequency, then the output signal may be very noisy and may also have a decreased amplitude. If the cut-off frequency is too low (RC constant is too high) relative to the sine frequency, then the final output signal through the RC circuit will be more likely to have a decreased amplitude, thus you'll only get a limited range of voltages. Below are some results from experimentation with varying sine frequencies.
-[[Image:10HzRC4-7.jpg|left|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 3.2V. ]]
+[[Image:10HzRC4-7.jpg|left|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 10Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 3.2V. ]]
-[[Image:30HzRC4-7.jpg|right|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.68V.]]
+[[Image:30HzRC4-7.jpg|right|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 30Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.68V.]]
-[[Image:20HzRC4-7.jpg|center|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
+[[Image:20HzRC4-7.jpg|center|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 20Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
 ==Sample Code==

@@ Line 50: / Line 50: @@
 [[Image:10HzRC4-7.jpg|left|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 3.2V. ]]
-[[Image:20HzRC4-7.jpg|right|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
+[[Image:30HzRC4-7.jpg|right|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.68V.]]
+[[Image:20HzRC4-7.jpg|center|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
 ==Sample Code==

@@ Line 48: / Line 48: @@
 This cut-off frequency can cause a loss in the output amplitude. The determination of if the cut-off frequency is too high depends on the sine frequency. If the cut-off frequency is too high (RC constant is too low) relative to the sine frequency, then the output signal may be very noisy and may also have a decreased amplitude. If the cut-off frequency is too low (RC constant is too high) relative to the sine frequency, then the final output signal through the RC circuit will be more likely to have a decreased amplitude, thus you'll only get a limited range of voltages. Below are some results from experimentation with varying sine frequencies.
-[[Image:10HzRC4-7.jpg|left|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads.]]
+[[Image:10HzRC4-7.jpg|left|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 3.2V. ]]
+[[Image:20HzRC4-7.jpg|right|frame|Oscilloscope reading of the sinusoidal analog output with a Sine Frequency of 25Hz with a resistor of 47 kOhms and a capacitor of 0.1 microFarads. The Peak to Peak Voltage reading is 2.96V.]]
 ==Sample Code==

@@ Line 46: / Line 46: @@
 where <math>f_c</math> is the cut-off frequency (<math>\text{Hz}</math>), <math>R</math> is the resistance (<math>\Omega</math>'s) and <math>C</math> is the capacitance (F).
-This cut-off frequency can cause a loss in the output amplitude. The determination of if the cut-off frequency is too high depends on the sine frequency. If the cut-off frequency is too high (RC constant is too low) relative to the sine frequency, then the output signal will be very noisy and not as clear. If the cut-off frequency is too low (RC constant is too high) relative to the sine frequency, then the final output signal through the RC circuit will be more likely to have a decreased amplitude, thus you'll only get a limited range of voltages.
+This cut-off frequency can cause a loss in the output amplitude. The determination of if the cut-off frequency is too high depends on the sine frequency. If the cut-off frequency is too high (RC constant is too low) relative to the sine frequency, then the output signal may be very noisy and may also have a decreased amplitude. If the cut-off frequency is too low (RC constant is too high) relative to the sine frequency, then the final output signal through the RC circuit will be more likely to have a decreased amplitude, thus you'll only get a limited range of voltages. Below are some results from experimentation with varying sine frequencies.
+[[Image:Example.jpg|Example.jpg]]
 ==Sample Code==

← Older revision		Revision as of 13:57, 21 May 2010
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	The PIC32 is actually incapable of directly creating an analog output. Instead, the PIC32 can perform pulse width modulation (PWM) to create an average analog output. At a given frequency, PWM varies the time that the output pin is on (output is 3.3V) to create the duty cycle which can simulate voltages between 0V and 3.3V. For example, if the duty cycle is 50%, the PIC32 holds the pin at 3.3V 50% of the time and 0V for the other 50%. The average output voltage is then 1.65V. If the pin is connected to an external RC circuit, the PWM can be integrated. By varying the duty cycle sinusoidally, the output with an RC circuit can resemble a sinusoid. Thus, to create the sinusoidal output, a sinusoidal wave must be divided into a discrete number of points. These points can then be converted to a list of duty cycles to represent the sinusoid.		The PIC32 is actually incapable of directly creating an analog output. Instead, the PIC32 can perform pulse width modulation (PWM) to create an average analog output. At a given frequency, PWM varies the time that the output pin is on (output is 3.3V) to create the duty cycle which can simulate voltages between 0V and 3.3V. For example, if the duty cycle is 50%, the PIC32 holds the pin at 3.3V 50% of the time and 0V for the other 50%. The average output voltage is then 1.65V. If the pin is connected to an external RC circuit, the PWM can be integrated. By varying the duty cycle sinusoidally, the output with an RC circuit can resemble a sinusoid. Thus, to create the sinusoidal output, a sinusoidal wave must be divided into a discrete number of points. These points can then be converted to a list of duty cycles to represent the sinusoid.

	The three most important parameters in creating the sinusoidal analog output are the the number of points per period, the RC time constant, and the sinusoid frequency. The combination of the ~~cutoff~~ frequency and the points per period helps tell the PIC when to change the duty cycle. The RC constant of an external RC circuit is important in creating smooth and accurate curves and in improving the quality of the output signal.		The three most important parameters in creating the sinusoidal analog output are the the number of points per period, the RC time constant, and the sinusoid frequency. The combination of the sinusoid frequency and the points per period helps tell the PIC when to change the duty cycle. The RC constant of an external RC circuit is important in creating smooth and accurate curves and in improving the quality of the output signal.

@@ Line 12: / Line 12: @@
 The equation governing the duty cycle is
-<math>duty cycle = \frac{MAX\_DUTY}{2y} + \frac{MAX\_DUTY}{2}</math>
+<math>duty cycle = \frac{MAX\_DUTY}{2}y + \frac{MAX\_DUTY}{2}</math>
 where the <math>MAX\_DUTY</math> is determined by the frequency of the PWM.