Digital Voltmeter. Embedded Systems lab University of Jordan. Spring 2012/2013

Transcription

1 Digital Voltmeter Spring 2012/2013 Embedded Systems lab University of Jordan Spring 2012/2013

2 Preferred Group Size Grading Project Due Date (3) Three is the allowed group size. The group can be from the same class (recommended), or from in between classes (allowed but highly discouraged) (15) 15 marks is the project weight, counted as part of the final examination. Project marks are not disclosed to students (21) Week starting 21st April General Description Have you ever wondered how the voltmeter that you used in the circuits or electronics labs works? In this project, you will design a digital voltmeter that can measure voltages from 0 to 15 volts. The block diagram of the system is shown in Fig. 1. Basically, and as in all voltmeters, the system has two probes that can be used to measure the voltage in some circuit. The positive probe is connected to three SPST switches that are used to select the voltage range. The voltage ranges that are supported by this voltmeter are 0-5, 0-10, and 0-15 V. The voltage read through this probe is fed to a conditioning circuit then to one of the analog channels of the PIC microcontroller which will be responsible for converting the value into digital format and displaying it on the LCD in decimal. The conditioning circuit is required in case the input voltage is expected to be greater than input voltage range of the A/D module of the PIC. Four pushbuttons are used in this voltmeter. Three of these are used to read the voltage after the corresponding range selection switch is closed. The fourth switch is the Power Save mode which basically puts the device in sleep mode to reduce power consumption. The voltmeter is equipped with a buzzer that is activated as long as the input voltage is outside the selected voltage range. Page 2 of 6

3 LCD Voltage Range Selection Switches Welcome to DVM! 0 5 V Conditioning Circuit 1 (+) Probe 0 10 V Conditioning Circuit V Conditioning Circuit 3 PIC16F877A Pushbuttons 0 5 V 0 10 V 0 15 V (-) Probe Power Save Buzzer Fig. 1. Block diagram of digital voltmeter. Project Details 1) Startup and Initialization When the system is powered up, the program should do all necessary initializations for the I/O ports, A/D module, and LCD. No measurements are allowed in the initialization phase until the LCD displays the message Welcome to DVM! even if one of the voltage range selection buttons is pressed. When the initialization phase is over, conversions can be started by pressing one of the range selection pushbuttons. 2) Voltage Range Selection Selecting the voltage range to be used is done by first closing the corresponding SPST switch then pressing the assigned pushbutton. This instructs the PIC to acquire the voltage from the assigned analog channel. The interface between the pushbuttons and the PIC should be done by using interrupts not polling. 3) Conditioning Circuit This circuit is required whenever the input voltage to be measured is expected to be greater than the reference voltage of the A/D; otherwise, the input voltage may damage the PIC input. In this project, the A/D module should be configured to use internal reference voltages (0-5V). Basically, this circuit should scale down the input voltage to match that of the A/D reference voltages. However, you should display the actual voltage on the LCD screen by writing the necessary code to reverse the scaling process on the converted value in your program. Page 3 of 6

4 4) A/D Conversion The A/D module is configured such that: a) Each input range is assigned to a different analog channel of the PIC. b) The reference voltages are internal c) You may use the eight most significant bits of the conversion result in your calculations. 5) LCD Display The LCD is primarily used to display the measured voltage. The displayed message on the LCD should contain the selected voltage range on the first line as well as the measured value on the second line. The measured value should be displayed using three decimal digits; two integers and one fractional digit, along with the decimal point. Additionally, the LCD should display the message Out of Range as long as the input value is greater than the selected voltage range. 6) Buzzer The buzzer is used to sound whenever the input value is greater than the selected input range. Turning off the buzzer should be done by selecting a different voltage range or entering the power saving mode. Remember that the LCD should also display Out of Range! when the buzzer is activated. 7) Power Save Mode In order to save the battery life of the device, the device can be put in sleep mode by pressing the Power Save pushbutton. Exiting this mode is done by resetting the PIC or by pressing any of the pushbuttons which should force the system to reinitialize. 8) Calculations Remember that value obtained from the A/D process is not actually the measured value! However, it is somehow related to it. Thus, you need to manipulate the value obtained after conversion in order to get the actual voltage in a 3-digit decimal number. In this project, you may only use the upper 8 bits of the 10-bit value produced by the A/D module. The code that you write to manipulate the converted value could be different, in part or in all, depending on the selected voltage range. Bonus 1. If any project is submitted before 10 th of April, 2 marks bonus is awarded. Any submissions before the official discussion dates will be awarded 1 mark. 2. If you expand the voltmeter to support measuring resistor values and it is fully working, 3 marks bonus is awarded for each student. Page 4 of 6

5 Important Notes Start as early as possible on your project, though the project description sounds simples, there is inherent complexity in both hardware and software aspects, so do not underestimate the time it needs, you will have many problems along the way which you will have to resolve! Never think of buying a model or commissioning someone to do it for you, not only will you get a zero in the project, but also your act will be considered as a direct violation to JU laws and your actions shall be reported as cheating in the final exam! Code sharing between groups is not allowed! If you acquire a part of your software from a book, website, etc kindly reference it properly, else it will be considered as plagiarism. You are free to use any material to build the model and the holding structure for the hardware devices you use. (You might use LEGO parts, wood, strengthened cartoon or even metallic components!!) All programming must be done in PIC ASSEMBLY language only; using high level languages in the project will get you a Zero. Your submitted work must be professional: 1. Hardware: you are submitting a product, all electrical and electronic components must be hidden from the user, only user-accessed components are visible, hide the wiring, be neat. Still, the instructor should be easily able to examine the internal components at the time of discussion when required! 2. Software: your work should be fully documented, all inputs/outputs should be listed, and each subroutine/macro should be fully documented! Use functional comments! Refer to the last section in Experiment 2 regarding documentation. You should submit two types of flowcharts: 1. An abstract general flowchart of the whole program. 2. A flowchart for each of your written subroutines/macros (LCD, Pushbuttons, Switches and/or those software codes taken from the lab experiments ARE NOT required) Students are not allowed to move between groups once they are formed, so choose your group carefully from the beginning! We are not responsible if your colleagues in the group chose to drop the class, we will not allow you to join another group! Divide the work such that each student is responsible for a specific task, YET EVERY student is required to answer for ANY QUESTIONS in relation to any submitted work of the Project. Page 5 of 6

6 Report Guidelines You should submit your report as a hard copy. Submission due date is on April, 21 st 2013 Your report should contain: 1. The flowcharts (as described above in the notes section) 2. Circuit diagram of your hardware (use Multisim or Proteus to draw the circuit, include the file as well) 3. Your calculations. 4. Any figures, tables which you find useful to include 5. The contribution of each student in the project! Other Project Proposals If you have another project idea which you would like to do instead! You should hand in a proposal (printed) describing in details the idea of your project, the hardware components you think you might use, number of students in this project to your direct engineer ONLY! She will notify you of the status of proposal acceptance/refusal! Proposals submissions deadline is March 28th, If you submit a project which has not been approved you will get a mark of Zero Good Luck and Have Fun Building the Project Page 6 of 6