ECE383: Microprocessors Lab 9 Analog-to-Digital and Digital-to-Analog Conversion with I 2 C Serial EEPROM Data Storage

Transcription

1 ECE383: Microprocessors Lab 9 Analog-to-Digital and Digital-to-Analog Conversion with I 2 C Serial EEPROM Data Storage Goals: The goals of this lab are to introduce students to a PIC24-based hardware system capable of analog-to-digital (ADC) and digital-to-analog (DAC) conversion with I2C Serial EEPROM data storage. The lab will require students to expand the PIC24 reference schematic to include a MAXIM 548 DAC and a 24LC515 I 2 C serial EEPROM and additional components. The laboratory will require students to wire SPIbased MAXIM 548A DAC and I 2 C-based 24LC515 integrated circuits into their PIC24- based Microstick II system and program the system to act as a data acquisition and storage device. 1. Introduction This lab introduces basic analog to digital data conversion using ADC module on the PIC24 processor and digital to analog conversion using the SPI-based MAXIM 548 DAC. A 24LC515 I 2 C serial EEPROM will be used to store data collected from the ADC module. The tasks in this lab include: Modify the PIC24 reference system schematic and printed circuit board (PCB) layout to include the MAXIM 548A DAC, the 24LC515 EEPROM and associated hardware. Wire a MAXIM 548A integrated circuit to the PIC24-based Microstick II system on the protoboard. Wire a 24LC515 integrated circuit to the PIC24-based Microstick II on the protoboard. Write a C program to program the Microstick II to act as a data acquisition and storage device. 2. TASK 1: PIC24 Reference System Schematic and PCB with MAX548A and 24LC515 For this task we will modify the previously designed schematic and printed circuit board layout to include the MAX548A and 24LC515 components. These components may be found in the component library located on the class website. You will need to download all three files to a directory where you can include them in your schematic and PCB. When complete, your PIC24 system schematic should closely resemble the schematic given in Figure 1. 1 P age

2 Figure 1. Updated PIC24 Schematic. For this task we will create a printed circuit board layout from the PIC24 schematic created as a part of a previous lab. The board size should be 80mm x 80mm. The board part number should be ECE383-LAB9 and the Revision Number should be 001. These parameters can be set through the PCB wizard. Use the Settings->Grids function to set the Working Grid and the Screen Grid to 1mm x 1 mm. Use the Settings->Coordinates function to set the Coordinate System Origin to the lower left corner of the board. Left click on the bottom edge of the board, press the = key and note the Y coordinate value. Left click on the left edge of the board, press the = key and note the X coordinate value. Enter the X and Y values for the Coordinate System Origin using the Settings->Coordinates function. This should set the origin to the lower left corner of the board as indicated by a symbol. Another method for setting the system origin is to highlight an item (i.e. the bottom edge of the board), right click and select Origins->Set System Origin At Item. We will create four mounting holes for this PCB using the Add->Board->Circle function. The diameter for each mounting hole should be 3mm and they should be placed in the four corners of the board with each hole being exactly 2mm from each edge of the board. Use the Tools->Measure function to assist you in this layout. Each of the components should be placed in specific locations on the PCB. Highlight a component and press the = key. This will allow you to type in exact locations for the origins of each of the components. Table 1 gives the X and Y values for the location of each component in your design. Component X location Y location PIC24 (U1) LM (U2) MAX548A (U3) P age

3 24LC515 (U4) SW LED R R R R C C C C C Table 1. Expanded PIC24 System Component Locations. Use the PCB Artist Add Text tool to place the text ECE383 LAB9 and all the names of your design team near the bottom left corner of your design. Select the name of each component and orient the name (using the r key) such that the names are all oriented in the same direction. Use your experience from previous labs to create a PCB similar to the diagram shown in Figure 2 below. Figure 1. Expanded PIC24 System Printed Circuit Board. Use the Output->Reports tool within PCB Artist and create a Design Rule Check Report and a Component Positions Report. 3 P age

4 Most printed circuit boards intended for fabrication include a ground plane. A ground plane on a (PCB) is a large area or layer of copper connected to the circuit's ground point. It serves as the return path for current from many different components. A ground plane is often made as large as possible, covering most of the area of the PCB which is not occupied by circuit traces. In multilayer PCBs, it is often a separate layer covering the entire board. Copper Pour is used to flood areas of a PCB layout with copper, usually connected to a nominated signal through thermal connections, typically Ground (GND) or VCC. This facility will then create voids around tracks, component pads, vias and other electrical obstacles. From the Add menu, select Copper Pour Area> Rectangle Other Pour Area options are available for adding different shapes. We will add the pour area to the Top Copper layer. Pour areas and poured copper can be added to any electrical layer. Create a rectangle that is one millimeter inside the outer board edges. Once the rectangle is created, left click to select one of the rectangle edges. Right click and, from the popup shortcut menu, select Pour Copper. A dialog is displayed from where you can select parameters for the poured area, such as the net name association and thermal connections etc. Select the GND Net name. Figure 4 shows the result of the copper pour process. Figure 4. Expanded PIC24 System Printed Circuit Board with Copper Pour. 4 P age

5 TA check: As soon as you enter the lab, show the TA the schematic diagram and the printed circuit board you completed. Include a printout of your schematic diagram and PCB with the copper pour in your lab report. Include the Design Rule Check Report and the Component Positions Report in your lab report. 3. TASK 2: MAX548A Wiring Wire the MAX548A integrated circuit to your Microstick: 1. Connect all required Vdd and Vss (GND) pins on the MAX548A to your system power and ground rails respectively. 2. Connect the LDAC# pin (pin 6) to Vdd. 3. Connect the CS# pin (pin 3) to RB5 (pin 14) on the PIC24 Processor. 4. Connect the DIN pin (pin 4) on the MAX548A to SDO1/RP6 (pin 15) on the PIC24 processor. 5. Connect the SCLK pin (pin 5) in the MAX548A to SCK1/RP7 (pin 16) on the PIC24 processor. Connect the wiper terminal of a thumbwheel potentiometer to pin AN0 of the PIC24 processor. Connect the terminal one of the potentiometer to Vdd and terminal three of the potentiometer to GND. Use the chap11/adc_spidac_test.mcp MPLAB project from the code library as the starting point for this task. Compile this project and download it to the Microstick to verify operation of the MAX548A. Connect the OUTA pin of the MAX548A to the oscilloscope to verify the analog output can vary between 0-3.3V. TA check: Show the TA that your code functions as expected, capture a screenshot of the console output of your code. Use a screen capture tool to capture output windows and include them in your lab report. Include your source language programs in your lab report. 4. TASK 3: 24LC515 Wiring Wire the 24LC515 integrated circuit to your Microstick: 1. Connect all required Vdd and Vss pins on the 24LC515 to your system power and ground rails respectively. Vdd may be labeled Vcc on the 24LC515 pin diagram. 2. Connect A1 and A0 pins to Vss. Connect the A2 pin to Vdd. 3. The WP pin should be left unconnected. 4. Connect the SCL pin (pin 6) on the 24LC515 to SCL1 (pin 17) on the PIC24 processor. 5. Connect the SDA pin (pin 5) in the 24LC515 to SDA1 (pin 18) on the PIC24 processor. 6. The SDA1 (pin 18) and SCL1 (pin 17) I 2 C pins on your PIC24 µc must have external pull-up resistors Kohm) Use the chap10/mcp24lc515_i2c_eeprom.mcp MPLAB project from the code library as the starting point for this task. Compile this project and download it to the PIC24 processor to verify operation of the 24LC515. TA check: Show the TA that your code functions as expected, capture a screenshot of the console output of your code. Use a screen capture tool to capture output windows and include them in your lab report. Include your source language programs in your lab report. 5 P age

6 5. TASK 4: PIC24 Data Acquisition and Storage Device System Write a program that samples the analog value on the AN0 input every 0.1 seconds and outputs the sampled value to the MAX548A DAC (HINT: consider use of a timer-based interrupt). Provide a console output similar to that in the adc_spidac_test.mcp MPLAB project to verify operation of your system. Every 0.5 seconds an 8-bit value from the AN0 input should be written to the 24LC515 EEPROM. After one minute of data sampling, you system should stop sampling the data and output all the sampled values from the 24LC515 EEPROM to the console. TA check: Show the TA that your program functions as expected and capture a screenshot of the console output of your code for your program. 6. Laboratory Report No later than a week from the day the lab is performed, provide the TA a printed copy of the lab report following the ECE383 Lab report Template given on the class website. Each lab group will submit one joint lab report to the TA. Your report should have the reporting requirements needed for Tasks 1-4. The TA will take off a significant number of points (15 points from total lab grade) if your C source does not have the required comments. 7. GRADING POLICY 1. Completion of Task 1 with results included in lab report (20%) 2. Completion of Task 2 with results included in lab report (20%) 3. Completion of Task 3 with results included in lab report (20%) 4. Completion of Task 4 with results included in lab report (20%) 5. Completeness, quality, and correctness of the lab report (20%) 6 P age