Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
learn:courses:unit-6:start [2017/03/27 22:59] – Marthalearn:courses:unit-6:start [2022/10/04 11:38] (current) – external edit 127.0.0.1
Line 1: Line 1:
- ====== Unit 6: Analog I/O and Process Control ======+====== Unit 6: Analog I/O and Process Control ====== 
 +[[{}/learn/courses/unit-5/start|Back to Unit 5]] 
 === Unit 6 Labs === === Unit 6 Labs ===
-  * [[https://reference.digilentinc.com/learn/courses/unit-6-lab6a/start|Lab 6a]] +  * [[/learn/courses/unit-6-lab6a/start|Lab 6a]] 
-  * [[https://reference.digilentinc.com/learn/courses/unit-6-lab6b/start|Lab 6b]]+  * [[/learn/courses/unit-6-lab6b/start|Lab 6b]]
  
  
 === Download This Document === === Download This Document ===
-  * {{ :learn:courses:unit-6:unit_6.pdf |Unit 6 PDF}}+{{ :learn:courses:unit-6:unit_6.pdf |Unit 6 PDF}}
  
  
Line 15: Line 17:
  
 ===== 2. Objectives ===== ===== 2. Objectives =====
-  * Generate PWM outputs to implement variable motor supply voltage. +  - Generate PWM outputs to implement variable motor supply voltage. 
-  * Implement a tachometer operation using PIC32 Timers. +  - Implement a tachometer operation using PIC32 Timers. 
-  * Develop MPLAB X projects that implement open-loop and closed-loop motor control. +  - Develop MPLAB X projects that implement open-loop and closed-loop motor control. 
-  * Develop the C program code to implement a PI controller and a moving average digital filter. +  - Develop the C program code to implement a PI controller and a moving average digital filter. 
-  * Manage multiple background tasks in an interrupt driven system. +  - Manage multiple background tasks in an interrupt driven system. 
-  * To monitor and display data from a process running in real-time. +  - To monitor and display data from a process running in real-time. 
  
 ---- ----
  
 ===== 3. Basic Knowledge ===== ===== 3. Basic Knowledge =====
-  * Suggested reading: [[https://www.elsevier.com/books/embedded-computing-and-mechatronics-with-the-pic32-microcontroller/lynch/978-0-12-420165-1|Embedded Computing and Mechatronics with the PIC32 Microcontroller]]+  - Suggested reading: [[https://www.elsevier.com/books/embedded-computing-and-mechatronics-with-the-pic32-microcontroller/lynch/978-0-12-420165-1|Embedded Computing and Mechatronics with the PIC32 Microcontroller]]
     * Basic circuit theory     * Basic circuit theory
     * Fundamentals of programming with C     * Fundamentals of programming with C
-  * How to configure I/O pins on a Microchip® PIC32 PPS microprocessor  +  - How to configure I/O pins on a Microchip® PIC32 PPS microprocessor  
-  * How to implement a real-time system using preemptive foreground – background task control +  - How to implement a real-time system using preemptive foreground – background task control 
-  * How to generate a PWM output with the PIC32 processor +  - How to generate a PWM output with the PIC32 processor 
-  * How to configure the Analog Discovery to display logic traces +  - How to configure the Analog Discovery to display logic traces 
-  * How to implement the design process for embedded processor based systems+  - How to implement the design process for embedded processor based systems
  
 ---- ----
Line 38: Line 40:
 ===== 4. Equipment List ===== ===== 4. Equipment List =====
 ==== 4.1. Hardware ==== ==== 4.1. Hardware ====
-  * [[http://store.digilentinc.com/basys-mx3-pic32mx-trainer-board-recommended-for-embedded-systems-courses/|Basys MX3 trainer board]] +  - [[https://digilent.com/shop/basys-mx3-pic32mx-trainer-board-for-embedded-systems-courses/|Basys MX3 trainer board]] 
-  * Workstation computer running Windows 10 or higher, MAC OS, or Linux +  - Workstation computer running Windows 10 or higher, MAC OS, or Linux 
-  * 2 [[http://store.digilentinc.com/usb-a-to-micro-b-cable/|Standard USB A to micro-B cables]] +  - 2 [[https://digilent.com/shop/usb-a-to-micro-b-cable/|Standard USB A to micro-B cables]] 
-  * [[http://store.digilentinc.com/motor-gearbox-1-19-gear-ratio-custom-12v-motor-designed-for-digilent-robot-kits/|5 V DC motor with tachometer]]+  - [[https://digilent.com/shop/dc-motor-gearbox-1-19-gear-ratio-custom-12v-motor-designed-for-digilent-robot-kits/|12 V DC motor with tachometer]] 
 +  - [[https://digilent.com/shop/5v-4a-switching-power-supply/|5V, 4A DC power supply]]
  
 In addition, we suggest the following instruments: In addition, we suggest the following instruments:
-  * [[http://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/|Analog Discovery 2]]+  - [[https://digilent.com/shop/analog-discovery-2-100ms-s-usb-oscilloscope-logic-analyzer-and-variable-power-supply/|Analog Discovery 2]]
  
 ==== 4.2. Software ==== ==== 4.2. Software ====
 The following programs must be installed on your development workstation: The following programs must be installed on your development workstation:
-  * [[http://www.microchip.com/mplab/mplab-x-ide|Microchip MPLAB X® v3.35 or higher]] +  - [[http://www.microchip.com/mplab/mplab-x-ide|Microchip MPLAB X® v3.35 or higher]] 
-  * [[http://www.microchip.com/SWLibraryWeb/product.aspx?product=PIC32%20Peripheral%20Library|PLIB Peripheral Library]] +  - [[http://www.microchip.com/SWLibraryWeb/product.aspx?product=PIC32%20Peripheral%20Library|PLIB Peripheral Library]] 
-  * [[http://www.microchip.com/xcdemo/xcpluspromo.aspx|XC32 Cross Compiler]] +  - [[http://www.microchip.com/xcdemo/xcpluspromo.aspx|XC32 Cross Compiler]] 
-  * [[http://store.digilentinc.com/waveforms-2015-download-only/|WaveForms 2015]] (if using the Analog Discovery 2) +  - [[https://digilent.com/shop/software/digilent-waveforms/|WaveForms]] (if using the Analog Discovery 2) 
-  * [[http://www.putty.org/|PuTTY Terminal Emulator]] +  - [[http://www.putty.org/|PuTTY Terminal Emulator]] 
-  * Spreadsheet application (such as Microsoft Excel)+  - Spreadsheet application (such as Microsoft Excel)
  
 ---- ----
  
 ===== 5. Project Takeaways ===== ===== 5. Project Takeaways =====
-  * How to read analog voltage with a PIC32 processor. +  - How to read analog voltage with a PIC32 processor. 
-  * How to use the PIC32 Output Compare to implement a PWM analog output. +  - How to use the PIC32 Output Compare to implement a PWM analog output. 
-  * How to use the PIC32 Input Capture period measurement to implement a tachometer. +  - How to use the PIC32 Input Capture period measurement to implement a tachometer. 
-  * The advantages of using period measurements as opposed to frequency measurements and vice versa. +  - The advantages of using period measurements as opposed to frequency measurements and vice versa. 
-  * Fundamental digital filtering concepts for data smoothing. +  - Fundamental digital filtering concepts for data smoothing. 
-  * Open-loop and closed-loop process control.+  - Open-loop and closed-loop process control.
  
 ---- ----
Line 109: Line 112:
 The //Analog Control Input// on the Basys MX3 processor board will be used as the variable input control. Figure 7.1 shows that the potentiometer is connected to PORT B pin 2 of the PIC32MX370. To use the PIC32 analog input connected to the potentiometer, we will need to assign RB2 as an analog input and then read the analog channel on a periodic basis. Analog channel 2 (AN2) is assigned to read the analog input on RB2. The ADC value of AN2 will vary from 0 to 1023 when the potentiometer output is varied from 0 to 3.3VDC. Initializing the ADC10 is not a trivial matter and following examples is the best approach rather than starting by attempting to unravel the data sheets.((Analog to Digital Conversion”, [[http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/adc|http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/adc]])) The ADC10 example in the Microchip PIC32 Peripheral Library of the MPLAB X Help can be used as a reference for developing the code to read one or more ADC channels. The //Analog Control Input// on the Basys MX3 processor board will be used as the variable input control. Figure 7.1 shows that the potentiometer is connected to PORT B pin 2 of the PIC32MX370. To use the PIC32 analog input connected to the potentiometer, we will need to assign RB2 as an analog input and then read the analog channel on a periodic basis. Analog channel 2 (AN2) is assigned to read the analog input on RB2. The ADC value of AN2 will vary from 0 to 1023 when the potentiometer output is varied from 0 to 3.3VDC. Initializing the ADC10 is not a trivial matter and following examples is the best approach rather than starting by attempting to unravel the data sheets.((Analog to Digital Conversion”, [[http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/adc|http://umassamherstm5.org/tech-tutorials/pic32-tutorials/pic32mx220-tutorials/adc]])) The ADC10 example in the Microchip PIC32 Peripheral Library of the MPLAB X Help can be used as a reference for developing the code to read one or more ADC channels.
  
-{{ :learn:courses:unit-6:fig-7-1.png?nolink&600 |Figure 7.1. Analog Input Control schematic diagram.}}+{{ :learn:courses:unit-6:unit_6_fig_7.1.jpg?nolink&700 |Figure 7.1. Analog Input Control schematic diagram.}}
 //Figure 7.1. Analog Input Control schematic diagram.// //Figure 7.1. Analog Input Control schematic diagram.//
 +
  
 Considering that the PIC32 ADC is connected to a potentiometer under manual control, the speed at which the analog voltage can change is relatively low. In Lab 6a and 6b we will run the PIC32 ADC at a high rate of speed so that the most recent ADC conversion will accurately reflect the current potentiometer setting. As Fig. 7.2 illustrates, the process of completing a single conversion consists of two phases: the sample phase and the conversion phase. The parameter $T_{AD}$ is the period on the ADC clock that can be an internal RC oscillator or the peripheral bus clock. From Fig. 7.1, we see that the input resistance is 10K ohms. According to the PIC32MX370 data sheet, the minimum $T_{AD}$ is 65 ns when the input resistance is 500 ohms. We will compensate for the elevated input resistance by extending the conversion time. Using a peripheral bus clock of 10 MHz, $T_{AD}$ is 100 ns and requires the minimum sample interval of 2 $T_{AD}$. Longer sample intervals result in more accurate conversions. If we set the sample rate to 250 KHz, then the conversion time, $T_C$, will be 4 µs, or 40 $T_{AD}$ clock cycles. TC is the sum of the conversion time and sample time as expressed by Eq. 7.1. Considering that the PIC32 ADC is connected to a potentiometer under manual control, the speed at which the analog voltage can change is relatively low. In Lab 6a and 6b we will run the PIC32 ADC at a high rate of speed so that the most recent ADC conversion will accurately reflect the current potentiometer setting. As Fig. 7.2 illustrates, the process of completing a single conversion consists of two phases: the sample phase and the conversion phase. The parameter $T_{AD}$ is the period on the ADC clock that can be an internal RC oscillator or the peripheral bus clock. From Fig. 7.1, we see that the input resistance is 10K ohms. According to the PIC32MX370 data sheet, the minimum $T_{AD}$ is 65 ns when the input resistance is 500 ohms. We will compensate for the elevated input resistance by extending the conversion time. Using a peripheral bus clock of 10 MHz, $T_{AD}$ is 100 ns and requires the minimum sample interval of 2 $T_{AD}$. Longer sample intervals result in more accurate conversions. If we set the sample rate to 250 KHz, then the conversion time, $T_C$, will be 4 µs, or 40 $T_{AD}$ clock cycles. TC is the sum of the conversion time and sample time as expressed by Eq. 7.1.
Line 200: Line 204:
  
 === 7.2.2. Analog Output: Pulse-width Modulation === === 7.2.2. Analog Output: Pulse-width Modulation ===
-In [[https://reference.digilentinc.com/learn/courses/unit-5-lab5a/start|Lab 5]], we used [[https://en.wikipedia.org/wiki/Pulse-width_modulation|pulse-width modulation]] to generate a communications signal of a constant frequency pulse train where the carrier frequency was turned on by setting the PWM output ratio to 9%, and off by setting the output PWM ratio to 100%. The information used to modulate the IR beam is contained in the amplitude modulation of the PWM carrier signal. In Labs 6a and 6b, the information is contained in the duty cycle of the PWM signal, which is a form of frequency modulation. This signal will be demodulated with low pass filtering to generate an analog control signal.+In [[/learn/courses/unit-5-lab5a/start|Lab 5]], we used [[https://en.wikipedia.org/wiki/Pulse-width_modulation|pulse-width modulation]] to generate a communications signal of a constant frequency pulse train where the carrier frequency was turned on by setting the PWM output ratio to 9%, and off by setting the output PWM ratio to 100%. The information used to modulate the IR beam is contained in the amplitude modulation of the PWM carrier signal. In Labs 6a and 6b, the information is contained in the duty cycle of the PWM signal, which is a form of frequency modulation. This signal will be demodulated with low pass filtering to generate an analog control signal.
      
 Lab 5 discussed the details of how to set up a PWM output using the output compare special function of the PIC32 processor. However, Lab 6a and 6b will require that we set up two PWM outputs that all use a common timer if the motor is to be capable of reversing direction. After initializing the timer to be used with the output compare and initializing the two output-compare channels, the PWM duty cycle of each individual channel is easily changed using the instruction //SetDCOCxPWM(DC);// where x denotes the PWM channel and DC is the compare setting. DC is computed by multiplying timer period register by the percent PWM. Provided that the two instructions used to modify the PWM duty cycle are completed within the PWM period, both outputs will simultaneously change their duty cycle at the end of the next PWM period.    Lab 5 discussed the details of how to set up a PWM output using the output compare special function of the PIC32 processor. However, Lab 6a and 6b will require that we set up two PWM outputs that all use a common timer if the motor is to be capable of reversing direction. After initializing the timer to be used with the output compare and initializing the two output-compare channels, the PWM duty cycle of each individual channel is easily changed using the instruction //SetDCOCxPWM(DC);// where x denotes the PWM channel and DC is the compare setting. DC is computed by multiplying timer period register by the percent PWM. Provided that the two instructions used to modify the PWM duty cycle are completed within the PWM period, both outputs will simultaneously change their duty cycle at the end of the next PWM period.   
Line 217: Line 221:
 Figure 7.10 shows the electric model of a permanent magnet brushed DC motor, such as the one shown in Fig. 7.3. The torque of the motor is proportional to the armature current labeled //Ia//. The armature winding resistance, Ra, and winding inductance, //La//, are fixed. The back electromotive force (EMF) is proportional to the speed of the motor.  Figure 7.10 shows the electric model of a permanent magnet brushed DC motor, such as the one shown in Fig. 7.3. The torque of the motor is proportional to the armature current labeled //Ia//. The armature winding resistance, Ra, and winding inductance, //La//, are fixed. The back electromotive force (EMF) is proportional to the speed of the motor. 
  
-{{ :learn:courses:unit-6:fig-7-10.png?nolink&600 |Figure 7.10. Electric model of a brushed DC motor.}}+{{ :learn:courses:unit-6:fig-7-10.png?nolink&400 |Figure 7.10. Electric model of a brushed DC motor.}}
 //Figure 7.10. Electric model of a brushed DC motor.// //Figure 7.10. Electric model of a brushed DC motor.//
  
Line 225: Line 229:
 The motor driver IC on the Basys MX3 processor platform is shown in Fig. 7.11. The motor wires used for power input and tachometer output are identified in Fig. 7.12. A 5.0 V external power supply is required to be connected to J11, marked as VBAR on the Basys MX3 processor board. A jumper must be used on JP1 to connect the 5V power, VBAR, to the motor supply, VM. The motor driver IC on the Basys MX3 processor platform is shown in Fig. 7.11. The motor wires used for power input and tachometer output are identified in Fig. 7.12. A 5.0 V external power supply is required to be connected to J11, marked as VBAR on the Basys MX3 processor board. A jumper must be used on JP1 to connect the 5V power, VBAR, to the motor supply, VM.
  
-{{ :learn:courses:unit-6:fig-7-11.png?nolink&600 |Figure 7.11. Basys MX3 Motor driver circuit.}}+{{ :learn:courses:unit-6:unit_6_fig_7_11.jpg?nolink&700 |Figure 7.11. Basys MX3 Motor driver circuit.}}
 //Figure 7.11. Basys MX3 Motor driver circuit.// //Figure 7.11. Basys MX3 Motor driver circuit.//
 +
  
 {{ :learn:courses:unit-6:unit_6_-_photo_4.jpg?nolink&600 |Figure 7.12. Basys MX3 connection to motor power wiring.}} {{ :learn:courses:unit-6:unit_6_-_photo_4.jpg?nolink&600 |Figure 7.12. Basys MX3 connection to motor power wiring.}}
Line 332: Line 337:
 Thus, the control signal is proportional to the integral of the error signal, and in part, directly to the magnitude of the error signal itself. Because of this, this approach to control is referred to as PI (proportional-integral) control. A distinct advantage of PI control is that using it results in zero steady state error for a first order plant (G1(s) = k/s). Now computers can’t solve equations in the continuous domain, therefore we must transform to a discrete domain that allows us to use samples of continuous signals. Eq. C.8 is the transformation from continuous to discrete time domain that is based upon rectangular integration. Ts is the interval between samples of the input. Thus, the control signal is proportional to the integral of the error signal, and in part, directly to the magnitude of the error signal itself. Because of this, this approach to control is referred to as PI (proportional-integral) control. A distinct advantage of PI control is that using it results in zero steady state error for a first order plant (G1(s) = k/s). Now computers can’t solve equations in the continuous domain, therefore we must transform to a discrete domain that allows us to use samples of continuous signals. Eq. C.8 is the transformation from continuous to discrete time domain that is based upon rectangular integration. Ts is the interval between samples of the input.
  
-$$s = ( \frac{1-z^{-1}}{T_s} ) \qquad (Eq. C.8)$$+$$s = \bigg( \frac{1-z^{-1}}{T_s} \bigg) \qquad (Eq. C.8)$$
  
 Completing the appropriate computations after substituting Eq. C.8 into Eq. C.7, we end up with a discrete time equation shown in Eq. C.9. Completing the appropriate computations after substituting Eq. C.8 into Eq. C.7, we end up with a discrete time equation shown in Eq. C.9.
Line 385: Line 390:
  
  
 +----
 +
 +[[{}/learn/courses/unit-5/start|Back to Unit 5]]
 +[[{}/learn/courses/unit-6-lab6a/start|Go to Lab 6a]]
 +[[{}/learn/courses/unit-6-lab6b/start|Go to Lab 6b]]
 +[[{}/learn/courses/unit-7/start|Go to Unit 7]]
  
 {{tag>reference learn microprocessor courses basys-mx3}} {{tag>reference learn microprocessor courses basys-mx3}}