ENGG1015: Lab 7. In Search of Light

Transcription

1 ENGG0: Lab 7 In Search of Light st Semester $ ' The goal of this lab is to complete the basic construction of the last stage of your project a light tracker. By doing so, you will learn to use an analog-to-digital converter (ADC) to bridge between the digital logic world of an FPGA and the analog circuit world. You will then combine the ADC circuit with the DAC circuit from last week to form the complete signal path. & % ' $ This lab is part of your project. The circuit you construct in this lab will be used directly in the project. Therefore: the equipment you will be using in the lab (breadboard, hardware tools, FPGA board, etc.) is also equipment for your project. the circuits and software design for this lab will be reused in the project. & % Equipment you ll use in this lab AND in project. Do not return them after this lab. You need to sign an equipment loaning form to keep them. (a) Multi-meter (b) Wire Kit (c) Breadboard 2 (d) ADC Module (e) DAC Module Figure : Materials for this lab (f) FPGA Cable

2 ENGG0 lab 7 Equipment you will use in this lab, but need to return after lab. (a) Light Tracking Head (b) FPGA Connector (c) Potentiometer Figure 2: Materials for this lab that must be returned.... You already know your lab partner You will be working with your project groupmate. To find your assigned lab partner and the assigned table,. Log in to Moodle. 2. Select the assignment Lab 7 Partner Please proceed to your assigned table Getting the Files Download the files for this lab from 3 Analog-to-Digital Conversion In this lab, you will connect an analog-to-digital converter (ADC) to the FPGA board. In contrast to the digital-to-analog converter (DAC) from last week, an ADC converts the value of an input analog signal to a digital representation for use in the system. Figure 3(a) shows the ADC module you will use for this lab. It has two connectors. The J connector on the ADC module should be inserted into JC I/O port of the Basys2 board. The J2 connector should be connected to the breadboard using an FPGA connector. Pin (a) ADC Module Name A0 GND A GND GND VCC Description Analog Input A0 Ground Analog Input A Ground Ground 3.3V (b) Pinout for J2 on the ADC module Figure 3: ADC module used to convert analog signals into digital values in the FPGA Page 2 of 8

3 ENGG0 lab 7 DO NOT connect to the FPGA yet. You will get the board once your TA has checked your circuit a b c d e f g h i j Pin Figure 4: Connection of the ADC module on the breadboard. 3. Hardware Construct the circuit in Figure 4 on the breadboard. Then connect the ADC module to the breadboard using an FPGA connector. Note the following: VCC of the FPGA connector is connected to the + row on top of the breadboard; GND of the FPGA connector is connected to the row on top of the breadboard The row at the top and bottom are connected together. 3.2 Getting the FPGA Board Show your constructed circuit on the breadboard to your TA and answer the following questions: The analog input of the ADC module is located at pin A0. Where is that connected to on the breadboard? What is the maximum value and minimum value of the analog input? Minimum Voltage: Maximum Voltage: You can take an FPGA from the TAs once you can answer the above questions. 3.3 Loading Software Open the file adc.xise in Xilinx ISE tools. It has the necessary controller for the ADC module (adctls8 already included). The adctls8 controls the ADC module to read the analog voltage value at the input A0. The voltage is represented digitally as an 8-bit data. The value of the 8-bit data n is computed such that V in n V cc 26 where V cc is the power supply to the ADC. In your case, it is 3.3V. Page 3 of 8

4 ENGG0 lab 7 In adc.sch, the output from adctls8 is connected to the special display module (displaydecm) that shows the value n in one of the 2 ways. By default, it displays the value n as a number between 0 and 2. When button 3 is pressed, it displays the voltage that should be present at the input. Now, using the Xilinx ISE tools, implement and download the design to the FPGA. Use a DMM to measure the input voltage Vin on the breadboard. Adjust the potentiometer and complete the following table: Vin dout (dec) 3.4 Checkoff Demonstrate the working ADC circuit to your TA and answer the following questions: Are the voltage values you measured the same as the display? Why/Why not? If the input voltage at Vin is Vcc /2, what is the value of dout? If the value of dout is 2, what is the voltage in Vin?... 4 Seeing the World In this section, you will experiment with a special laser head that you will use in the project as the final stage. A laser head is shown in Figure. Figure : Photo of a Laser Head There are two photoresistors located on the laser head. These photoresistors are the same as the one used in the ball counting tunnel from Lab 4. As a reminder, the resistance of a photoresistor decreases when the light intensity shining on it increases. Also included in the laser head is a laser module that you will use in the project. Figure 6 shows the schematic of the laser head as well as the connector pin assignment. 4. Left or Right? With the two photoresistors positioned at 90 to each other they are used as a way to detect the direction of a light source. In the following space, the laser head connector is shown with the 2 photoresistors on the laser head connected. Page 4 of 8

5 ENGG0 lab 7 Cable Connector 9 0 RR Laser Head Cable Laser Head Internal R R COM RL L+ 2 L- 00 Ω R L Figure 6: Connector pin assignment of the laser head Label the pin with VCC, GND, and VIN such that: When the light source is 0 in front of the laser head, V in should be V cc /2; When the light source is 4 to the RIGHT of the head, V in should be 0V; When the light source is 4 to the LEFT of the head, V in should be V cc. R L R R 4.2 Connect it up Remove the POT from your breadboard. Based on your circuit above, connect the laser head to the breadboard such that VIN is connected to the input of the ADC module. 4.3 Relating Angle to Voltage Complete the following table that relates the angle of the light source and V in. The polarity of the angle is defined in Figure 7. Page of 8

6 ENGG0 lab 7 θ 4 4 Figure 7: Defining angle of light source relative to the laser head Angle θ (degree) dout (dec) Plot the results in the following graph: Page 6 of 8

7 ENGG0 lab Checkoff 2 Show to your TA your complete circuit and the measurements above. Answer the following questions: In what range of θ is the voltage V in linearly proportional to θ? Assume V in = k s θ, what is the approximate value of k s from your measurement? Part and Part 6 can be proceeded in parallel. Split your group into 2 such that your group can work on both parts at the same time. The goal for these two parts is to connect the ADC circuit your have constructed so far with the DAC circuit from lab 6. The result will be a complete system that can control the speed of a motor by the angle of the light on the laser head Driving Motor Software This part is an extension to the FPGA design from last week. Open the project file adda.xise using Xilinx ISE tools. In this project, open the schematic file adda.sch. adda.sch contains the same ADC controller from above. Your task is to pass the digital value dout directly as din to the DAC from last week. Recall that you need to use the block dactls to control the DAC module. Display the value dout to the display module displaydecm like before. Refer to the project dac.xise from last week s lab for reference Driving Motor Hardware This part is almost identical to the hardware part of last week s lab. The goal is to connect the DAC module to the breadboard, and use an op-amp to drive a motor. Instead of using the switches to serve as input to the DAC, your partner is using the input from the ADC module to control the speed of the motor. Figure 8 shows a similar breadboard connection to the one from last week. Construct the circuit as an extension to the ADC circuit already on the breadboard. A few points to remember: Connect only VCC from FPGA to the top row marked +. It is 3.3V. Connect only 6V to the bottom row marked +. Only the op-amp requires 6V as power. Connect the row from top and bottom. They represent GND. Use a separate motor without the laser head in this step to test the connection. You will eventually connect to the motor of the laser head next week. Page 7 of 8

8 ENGG0 lab a b c d e f g h i j To Power Supply CH2 (6V) Pin Pin Pin Figure 8: Full circuit with ADC, DAC, laser head, and motor connections. 6. Checkoff 3 Show to your TA the complete circuit with ADC and DAC working to drive a motor. Answer the following questions: When the light source is on the LEFT side of the laser head, what direction is the motor turning? Suggest one way to reverse the rotation direction of the motor by changing the connection on the breadboard. Without changing the breadboard connection, can you reverse the direction of rotation of the motor? Save all your work! ISE project files breadboard connection They will be used in your project. Page 8 of 8