ECEN 1400 - Introduction to Digital and Analog Electronics

Peter Mathys, Spring 2014

Lab 10: The Digital Clock Project

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Goals of this Lab

The digital clock project is an individual effort. Each student has to design and implement their own clock, demo the working of the clock, and turn in an individual final project report. Feel free to discuss your plans with others and help others or get help from them. But you will not get credit for a design that is just a copy of someone else's design.


Milestone M1: Functional Block Diagram (2 points, 0.5 point extra for being on time). In labs 7, 8 and 9 you built basic versions of all the essential pieces needed for a digital clock. To start on the design of your clock, break the whole system down into functional blocks such as the seconds, minutes, and hours counter, the timing oscillator, the display, the set logic, the power supply, etc. Specify how the functional blocks interface with each other, e.g., the counters represent minutes and hours as binary coded decimals (BCD), the counters all run from a common clock and are enabled and disabled using a separate signal generated by the preceding stage, the power supply delivers 5Vdc with a maximum current of 1A, etc. Start from a sketch of how the functional blocks will be interconnected and then use Multisim to draw a schematic. You may want to verify the correct operation of some crucial functional blocks by setting up a simulation for individual blocks in Multisim. Some points to consider are:

Milestone M2: Complete Design and Bill of Materials (2 points, 0.5 point extra for being on time). At this point you should have a completed design with a full schematic in Multisim. Now you need to decide how to implement the design, either using WireWrap, soldering on a general purpose PCB, soldering on a custom designed PCB, or using a combination of implementation methods. Use the reporting tool in Multisim to create a bill of materials (BOM) and check this with your TA to make sure you have the right parts (so you can order them) and in the right form factors (so they will fit on the circuit board).

After you complete this milestone, start getting all of your parts, either from the EE store, another local source like RadioShack or J.B. Saunders, or by ordering them. Consider combining orders with other students to cut down on shipping costs and take advantage of higher volume discounts. If you make your own PCB get it designed, checked, and ordered. Keep in mind that the turnaround time for a custom PCB is about 1 week.

Milestone M3: Parts in Hand, Started Building and Testing Modules (2 points, 0.5 point extra for being on time). At this point you should have all parts purchased and in-hand, including either a general purpose or a custom designed printed circuit board, and you should have started the process of building and testing parts of your clock design. A good approach is to build each of your functional blocks from milestone M1 and test them independently. For example, use a function generator as input signal for a block and look at the output of the block using the oscilloscope. Compare the output of each block to your simulated or calculated results. Test for special conditions such as the rollover from 11:59 to 12:00. Test the function of input and output devices (switches and LEDs). Test aggressively to try to find problems, not meekly in the hopes of not finding any.

Demonstration of Working Clock. You must demonstrate your working clock to your TA in the lab (or by special arrangement) on or before the last day of classes. The TA will instruct you to demonstrate specific features of the clock and/or make measurements, e.g., of the timing frequency.

Final Report. The last part of the project is to complete the final report. The main function of this report is to describe how you designed your circuit, document how you implemented it in the form of a complete schematic, and indicate how well it performed or what would have to be changed in a future version. Imagine that a year from now you are the TA for ECEN 1400 and you need to tell your students what you did in your project. Your report should be written in such a way that you could easily get that information in 15-20 minutes by reading the report.


Hierarchical Design in Multisim

You can start a functional block diagram in Multisim by making use of hierarchical blocks, see Section 4.2 of the Multisim User Guide. An example for a 4-digit clock display is shown in this schematic which was saved as ClockDesign001.

Hierarchical Block Schematic for Clock Design in Multisim

The block labeled BCDto7Seg is a separate design that is used as a functional block in ClockDesign001. Initially, this design may be empty except for the connection pins as shown below.

BCDto7Seg Block Placeholder in Multisim

The detailed circuitry can then be added later to the BCDto7Seg design and will automatically be incorporated through the hierarchical block feature in the ClockDesign001 design. In this way you can start with a high level design and fill in more details later on.

Grading and Extra Credit

Download the Clock Project Score Sheet.

Grading Rubric. The clock project is worth 25 points (25% of 100 points for the semester). After completing the milestones you will have 6 points already (7.5 points with extra credit). The remaining 19 points are split up as follows:

  1. 9 pts: Hours and Minutes Display. Your clock has to display hours and minutes in some fashion. Each digit should roll over at the appropriate time if you are using a digital display.
  2. 3 pts: Accurate Oscillator. We will measure the frequency of your oscillator to determine if the timing frequency is accurate to within a factor of 0.995 to 1.005.
  3. 3 pts: Time Set. You must be able to set the time of your clock. There are various ways to achieve this and grading will reflect the sophistication of the method you choose.
  4. 4 pts: Working Power Supply. Your power supply must supply the required voltage(s) and current(s) for your clock.
  5. -3 (minus 3!) pts: Breadboard Only. You don't wire-wrap, solder, and/or create your own circuit board, but the clock still works on one or more breadboards.
  6. -5 pts (minus 1...5!): Project Report Problems. Points will be subtracted for incomplete or inadequate project reports.

The basic clock must display hours and minutes and accept a time (i.e., you can set the clock) to moderate accuracy. Full credit also includes:

Extra Credit. Extra credit is available, up to a total maximum score of 35 points (out of 25). If you have other good ideas than the ones listed below, ask and we'll include them in the list.

Project Report

Each student needs to write his or her own project report. This should be a concise document that describes the design process and contains the schematics of all parts with an explanation of how each part works. You also need to state how well each part of the design worked and what measurements you took to judge the success of your project. If some part is not working as expected, describe what changes you would propose to correct the problem. In the conclusion state what you learned from the project and what you would do different next time.

Specific Project Report Requirements:

  1. Description of your project.
  2. Full schematic with labeled blocks.
  3. Complete parts list.
  4. Answers to design issue questions.
  5. Important simulation results.
  6. Debugging problems and solutions.
  7. Characterization of the overall performance of your project implementation.
  8. What did you learn and what would you do different next time.
  9. Advice for future students.


Resources and Examples

Electronic Component Distributors

Clock Projects on the WWW: