Title image Fall 2019

Project 3: Reaction Timer

Purpose: to start exploring sequential digital circuits by creating a reaction timer game.


Problem Statement: The purpose of this project is to build a circuit that will test your reaction time. You will need a 7-segment display driver, a timer state machine, and a top-level graphic design file.

The circuit should work as follows. It begins in an idle state with two digits displaying zeros. When the user hits the start button, the circuit should light up a red LED and wait for a period of time. Then the circuit should display a green LED and start counting (approximate milliseconds), showing the count on the two digits. When the user hits the reaction button, the count should stop and freeze. If the user hits the reaction button before the green LED lights up, the counter should show FF and the system should go back to the idle state. When the user hits the start button, the digit display should be set back to zeros.

  1. Setup

    Make a new subdirectory for your project. Copy your 7-segment driver file from project 2 (bdf or vhd) to your new project directory.

  2. Make a new Quartus project

    Start Quartus and then create a new project. Call it reaction (you are welcome to call it whatever you like, but I will refer to the project and the top level file as reaction).

    Open your 7-segment driver file, then select Project->Add to project. Then select File->Create/Update->Make symbol file.

  3. Define the state machine behavior

    1. Define the entity and port for the circuit

      Create a new VHDL file with an entity called timer and name the file timer.vhd. Insert the Moore state machine template. The reaction circuit should have a clock, a reset, a start input, and a react input. It should have three outputs: one 8-bit std_logic_vector that sends the time (in ~ms) and two std_logic output signals that control the red and green LEDs.

    2. Define internal variables for the circuit

      Name the states for your state machine as sIdle, sWait, and sCount. Your circuit should initially be in the sIdle state. When the user hits the start button it should move to the sWait state, stay there for a while, and then move to the sCount state. When the user hits the react button, the sCount state should move back to the sIdle state. If the user hits the react button while the system is in the wait state, then the counter should be set to all 1s and the system should go back to the sIdle state.

      In order to both wait and count, you need an internal counter. Create an internal signal of type unsigned with 28 bits. Put its declaration between the architecture statement and the begin, along with the state signal declaration. You'll also need to add use ieee.numeric_std.all to your header section above the entity statement.

        signal count : unsigned (27 downto 0); 
    3. Define the behavior on reset

      Set up the reset condition so it activates on a '0'. It should set the state to sIdle and set the count to all zeros (28 of them).

    4. Define the behavior on a rising edge

      Set up the rest of the state machine. Use the count variable to both have the circuit wait a while and to count how long the user's reaction is. If you set count to what is effectively a large negative number and add one to it, you will eventually get to 0 (which is an easy test).

  4. Define the output behavior

    For the output, get rid of the second process statement in the template. Replace it with a few simple conditional signal assignments (remember, they all run in parallel all the time).

    1. Assign '1' to the green LED when state is equal to sCount and otherwise '0'.
    2. Assign a '1' to the red LED when state is equal to sWait, otherwise '0'.
    3. Assign a string of 8 zeros to mstime when the state is sWait, otherwise assign it bits 23 downto 16 of the internal counter. You'll need to cast it to a std_logic_vector using the function std_logic_vector().
  5. Connect the pieces of the circuit

    Create a new bdf file to be the top level file for your project. Call it reaction.bdf. Within it, place two instances of your 7-segment driver and one instance of the timer. Set up appropriate inputs and outputs for the circuit. (As an extension, make your top level file a VHDL file and use component and port map statements to connect the various elements.)

  6. Test your circuit

    Compile your circuit, assign pins, and then test it out. Document your circuit's behavior.



Create a wiki page with your report. For each task, write a short description of the task, in your own words.


Give your wiki page the label cs232f19project3.

Put your bdf and VHDL files in a folder called project3 in your CS232 private subdirectory on the Courses server.