ECE 103 In-Class Exercise L1 Guide

Transcription

1 ECE 10 In-Class Exercise L1 Guide Hardware and software needed to complete this lab exercise LabJack U, USB cable, and screwdriver (Qty 1) Red LED (Light Emitting Diode) Short lead is cathode (negative) (Qty 2) 1 kω resistor, Color bands: BROWN, BLACK, RED (Qty 1) 74LS00 2-input NAND gate IC (Qty 2) Push-button switch Protoboard & Jumper Wires Microsoft Visual Studio on a computer with a LabJack driver + Programming Reference ljerror = eget (ljhandle, LJ_ioGET_DIGITAL_BIT, FIO#, &InState, 0); Read from digital FIO Write to digital FIO Read from analog FIO Write to analog DAC Example: Read the logic state on FIO5 and save it to variable ival ljerror = eget (ljhandle, LJ_ioGET_DIGITAL_BIT, 5, &ival, 0); Variable ival will be either 0 (logic Low) or 1 (logic High) as measured by channel FIO5 ljerror = eput (ljhandle, LJ_ioPUT_DIGITAL_BIT, FIO#, OutState, 0); Example: Output a 1 (logic High) on FIO4 ljerror = eput (ljhandle, LJ_ioPUT_DIGITAL_BIT, 4, 1, 0); Syntax for enabling a channel for analog input: ljerror = eput (ljhandle, LJ_ioPUT_ANALOG_ENABLE_BIT, FIO#, 1, 0); Syntax for reading from an analog channel: ljerror = eget (ljhandle, LJ_ioGET_AIN, FIO#, &InVolt, 0); Example: Read the analog voltage on FIO2 and assign the voltage to variable ival ljerror = eput (ljhandle, LJ_ioPUT_ANALOG_ENABLE_BIT, 2, 1, 0); ljerror = eget (ljhandle, LJ_ioGET_AIN, 2, &ival, 0); ljerror= eput (ljhandle, LJ_ioPUT_DAC, DAC#, VDAC, 0); Example: Generate 2.5V on DAC0 channel ljerror = eput (ljhandle, LJ_ioPUT_DAC, 0, 2.5, 0); Input args: FIO# = 0 to 19, DAC# = 0 or 1, VDAC = 0 to 5 V, OutState = 0 (low) or 1 (high) Output args: InState = 0 (low) or 1 (high), InVolt = 0 to 2.44 V ljhandle LabJack ID handle, ljerror error status after operation 1

2 A Note on Microsoft Visual C Language Extensions For this In-Class Exercise, you will use certain Microsoft Visual C functions to accomplish tasks that would be difficult or impossible to do with pure C90/C99 code. Prototypes for three useful extensions are: int _kbhit ( void ); Checks console for keyboard input. It examines the input buffer directly and does not pause. Parameters : None Returns : A nonzero value if a key has been pressed. Otherwise, it returns 0. Remarks : The _kbhit function checks the console for a recent keystroke. If the function returns a nonzero value, a keystroke is waiting in the buffer. The program can then call _getch or _getche to get the keystroke code value. Header : <conio.h> void Sleep ( unsigned long Timeout ); Suspends (pauses) the execution of the current thread until the time-out interval elapses. Parameters : Time-out interval in milliseconds Returns : None Header : <Windows.h> Example : Sleep(200); /* Pause program for 200 milliseconds */ unsigned long GetTickCount ( void ); Retrieves the number of milliseconds that have elapsed since the system was started (up to 49.7 days ago). Parameters : None Returns : Elapsed time in milliseconds Header : <Windows.h> Example : t = GetTickCount(); /* If t contained 1245, it would mean 12,45 ms */ /* had elapsed since the system was started. */ 2

3 Part 1: Monitor switches using a LabJack and a C program In this section, you will create a C program that controls a LabJack to monitor two mechanical pushbutton switches. One switch will be configured for digital input, while the other will use analog input. If the digital switch is pressed, the LED will turn on. If the analog switch is pressed, the LED will turn off. The program will also update a count up/down variable on each switch press. Exercise 1A: Use a digital input channel on the LabJack to sense Switch #1 Construct the first switch circuit and LED circuit (see Figure 1) on the protoboard. LabJack FIO4 Switch #1 R pull-up +. V FIO5 + Red LED Sense FIO4 Figure 1: Connection diagram Figure 2: Internal FIO circuit Figure : Switch Pinout How does the digital input switch circuit work? (See Figure 2) a) FIO4 is configured as a digital input channel. b) The momentary contact switch in the LabJack parts kit is a mini push-button. The switch is normally open, so no electrical current will flow through it until the button is pressed. c) When the switch is closed (button pressed), the ground connection pulls the FIO4 input level down to 0 V. This is sensed as a logic low state. d) When the switch is opened (button not pressed), the internal pull-up resistor in FIO4 pulls the input level up to +. V. This is sensed as a logic high state. Summary: Button pressed 0 (logic low) is sensed. Button not pressed 1 (logic high) is sensed. FIO5 is configured as digital output. A low output turns off the LED, while a high output turns on the LED. An extra resistor is not needed due to the channel s internal current-limiting resistor.

4 C Project Setup Create a Microsoft Visual C/C++ Project 1. If it is not already running, start Microsoft Visual Studio (or Visual Studio Express). 2. The main Visual Studio window will appear. If the Solution Explorer pane is not visible, select View Solution Explorer from the menu bar. Click the New Project option on the Start Page. (Alternate method: Select File New Project from the menu bar.). The New Project window will appear. On the left side of this window, select "Visual C++" under Templates. In the center section, select "Win2 Console Application". In the Name input box, enter a name you would like to use for your project. In the Location input box, enter a directory where you would like to save your project. Click [OK]. 4. The Win2 Application Wizard window will appear. Click [Next >] to show the next wizard page. On the left-side of this window, select Application Settings. Under Application type, select Console application. Under Additional options, check Empty project. (The Precompiled header option will be grayed-out automatically.) Click [Finish]. 5. The Solution Explorer pane will show your newly created project. These folders should be visible: Header Files, Resource Files, and Source Files. Right-click the Source Files folder in the solution explorer. Select Add New Item from the pop-up menu. 6. The Add New Item window will appear. On the left side of this window, select "Visual C++" under Installed. In the center section, select "C++ File (.cpp)". Note: Don t worry that you chose.cpp instead of.c. This is fixed in the next step. In the Name input box, enter a source filename with a.c extension (e.g., prog.c). Click [Add]. If the file is successfully added, you will see the name of the newly created file inside the Source Files folder. 4

5 Add the LabJack Library This step specifies that the LabJack library file should be linked to the project. The library contains the low-level code needed to interface your program to the LabJack hardware. 1. Right-click the name of your project in the Solution Explorer pane. 2. Select Add Existing Item from the pop-up menu.. The Add Existing Item window will appear. Using the pop-up window s browser, navigate to and select the following file: C:\Program Files\LabJack\Drivers\LabJackUD.lib Click [Add]. If a message appears that asks if you want to create a new rule file, click [No]. If the file is successfully added, you will see its name below (not inside) the Source Files folder. Get the following file from the course website: Switch_LED_program.c 1. Copy and paste the contents of the file into the editor window. 2. Select File Save from the menu bar to save the source code. Compiling the Program 1. If the Output pane is not visible, select View > Output from the menu bar. 2. To build (compile) your program, choose one of these methods: Select Build > Build Solution from the menu bar -or- press the F7 key on the keyboard. The output of the build is displayed in the Output pane. If the code compiled successfully, the last line should be: "Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped" If the code did not compile successfully, the Output pane will show a list of errors. Double-click an error in the list to move the cursor to the offending line in the source code. Fix any problems and rebuild. Running the Program For a console application, output will appear in a separate pop-up window. To run your program and keep the output window open after it is done: Select Debug > Start Without Debugging from the menu bar. Press CTRL+F5 on the keyboard. Verify that your circuit and the program work as expected. 5

6 Exercise 1B: Use an analog input channel on the LabJack to sense Switch #2 Add the second switch circuit (see Figure 4) to the other circuit you already built on the protoboard. VS = +5 V LabJack FIO6 Rpull-up = 1 kω Switch #2 Figure 4: (Other switch & LED not shown) How does the analog input switch circuit work? a) FIO6 is configured as an analog input channel. b) When the switch is closed (button pressed), the ground connection pulls the FIO6 input level down to 0 V. c) When the switch is opened (button not pressed), the external resistor pulls the FIO6 input level up to +5 V. Note: When a LabJack U-LV FIO channel is configured for analog input, it is designed to accept overvoltages of up to +10 V without damage. However, the LV model can only accurately read voltages up to V. Hence, the +5 V input level will register as between 2.44 to 2.5 V. The LabJack U-HV AIN channel is designed to accept over-voltages of up to+40 V without damage. However, the HV model can only accurately read voltages up to +10 V. The +5 V input level should register as about 5 V. Since an analog input is used, it will sense the actual voltage present on the channel. To decide whether the switch is open or closed, you need to test if the measured voltage is above or below a selected threshold value (e.g., midway between 0 V and the maximum expected voltage). Perform the Part 1 Exercise 1B tasks in the Exercise Worksheet. 6

7 Part 2: Monitor a NAND Gate Circuit You will make the LabJack sense the output logic state of a 2-input NAND gate Exercise 2A Disassemble and remove the components from Part 1. Construct the circuit below (see Figure 5) on the protoboard. VS Switch #1 1 kω 1 kω 74LS FIO4 LabJack DAC0 Red LED + Switch #2 Figure 5: Connection diagram o o o Use two push-button switches for the NAND gate inputs. Add 1 kω resistors to the NAND inputs to pull the voltage high when the switches are open. Use one of the 2-input NAND gates in the 74LS00 IC chip (see Figure 5). For example, use Pin 1 and Pin 2 as the NAND inputs and Pin as the NAND output. notch V CC Figure 6: 74LS00 NAND gate pinout Connect Pin 14 (V CC) to VS (+5 V) on the LabJack. Connect Pin 7 () to on the LabJack. Do not connect VS to the output pins on the gate. It will damage the IC chip! Get the following file from the course website: NAND_program.c 1. Copy and paste the contents of the file into the editor window. 2. Select File Save from the menu bar to save the source code. Perform the Part 2 Exercise 2A tasks in the Exercise Worksheet. 7