Electrical and computer engineering come together in the design, implementation and testing of digital electronics. Digital circuits form the basis for computers, peripheral devices, process controllers and many other devices.

Digital circuits are based on Boolean algebra. In fact, digital electronic components are simply a realization of Boolean algebra functions. A digital circuit constructed by connecting the outputs of digital components to the inputs of other digital components is an implementation of a Boolean function.

In this lab, you will investigate the use of digital electronics in the control of an alarm buzzer in an automobile. Your circuit will use digital signals from sensors that detect when a door is open or the motor is running to determine when to sound the alarm.

The design of a digital circuit involves multiple steps. First, you will develop a written description of the operation of your circuit. Next, you’ll use a simulation program called LogicWorks to model your circuit. Simulations are often used to test circuit designs because (as you will discover) it’s typically much easier to draw the circuit on a computer than it is to build the circuit out of hardware and wires.

In this lab, you will first simulate your circuit design to verify that it is correct, and then you will implement your circuit in hardware and confirm that it functions correctly.

Design and construct a simulation for a digital circuit to control an alarm buzzer in a car. The alarm will warn about driving without buckling seatbelts, leaving the key in the ignition or leaving the lights on. Here is a more detailed description of the operation of your circuit:

To construct your digital circuit, assume you have five sensors that generate digital signals:

Signal name	Sensor	If signal = 1	If signal = 0
K	key	Key in ignition	Key not in ignition
D	door	Door open	Door closed
M	motor	Motor running	Motor not running
L	lights	Lights on	Lights off
B	seatbelt	Belt buckled	Belt not buckled

To complete the implementation of your digital circuit, use:

• AND, OR, NOT (inverter), NAND gates
• LEDs to demonstrate the output
• Switches to simulate signals from sensors (we will use wires for the switches in the implementation)

1. Five switches, representing the input from the digital sensors, will provide input to your digital circuit.
2. The signals from the five switches will be combined with digital logic components (AND, OR, NOT, NAND) into a control circuit.
3. The digital circuit will have a single output, which will be 1 to sound the alarm and 0 otherwise.

Record the work from each step below for inclusion in your lab notebook.

1. Develop a Boolean algebra expression that describes your digital circuit on paper. This expression should describe the three conditions under which the alarm should sound and the logic to cause the alarm to sound if any of the three conditions are true.
2. Convert the Boolean expression to several logic circuit diagrams, utilizing AND, OR, NOT, NAND gates. Read the section below on hardware implementation, and present at least three designs, using four ICs, three ICs, and two ICs.
3. Use LogicWorks to develop a simulation of your digital circuit for the case with two ICs (NAND gates). Annotate the components and signals in your digital circuit with brief text descriptions or explanations.
4. Test your digital circuit in LogicWorks to confirm that the buzzer sounds when (and only when) required by the problem specification. To ensure complete testing, write out the complete truth table for your Boolean expression, and verify that the circuit functions properly for each row. (Note that there will be 32 rows in your truth table!)
5. After testing, show your instructor your truth table, and give a brief demonstration of your LogicWorks simulation.
6. Print a copy of your LogicWorks simulation and put it in your lab notebook.

Decide which integrated circuits (ICs) or "chips" from Figure 1 you will use to implement your circuit. Note that a three-input OR gate is not available.

There is an obvious implementation that uses 4 ICs. Please find a more efficient implementation that uses only 3 ICs. Also, use NAND gates to find an implementation that uses only 2 ICs. We will simulate and implement the 2 IC solution.

1. Use scissors to cut out the ICs that you will use in your circuit implementation. Decide where you will place each IC on the circuit board in order to simplify and organize the wiring. There is no single right way to place the ICs, but some layouts will be more difficult to wire and debug than others.
2. Paste the ICs on a piece of paper using the layout that you will use on the circuit board. Draw lines to indicate all of the wires that you will need to connect in order to implement your circuit design. Include wires to Vcc (+5 volts) and GND (ground) to power the ICs, and also show the inputs K, D, M, L, B and the output to the LED.
3. Five long wires will be used to represent the input from the sensors. Each wire will be labeled with a piece of tape indicating K, D, M, L, B, and you can connect each wire to +5 volts or 0 volts (ground) to indicate various conditions.

The output of your logic circuit will be an LED, even though your description stated that a buzzer would sound. An LED is used because it is much easier to wire than the circuitry associated with a buzzer. An LED passes current in only one direction, so if it does not light for a logic "1", just turn it around. The resistor is needed to limit the amount of current that flows through the LED and the integrated circuit (IC) chip.

1. Review the circuit layout and wiring diagram that you prepared on paper before arriving at lab today.
2. Place the ICs on the circuit board according to your wiring diagram.
3. Using the supplied wires, connect the ICs according to your wiring diagram. Use a color-coding scheme to organize your wiring.
4. Use five long wires as your sensor inputs. Connect these wires to your logic circuit and to either +5 volts or 0 volts to test the various conditions. You might want to label these wires with K, D, M, L, B to simplify your testing.
5. Wire a Light-Emitting-Diode (LED) to serve as your buzzer and connect it to the output of your logic circuit.
6. Verify that the circuit operates as expected by testing all input combinations in the truth table that you completed in the first lab session.
7. Demonstrate your circuit to the instructor by showing correct operation for several test cases.

Your Boolean expression for the design, logic circuit diagrams that corresponds to your Boolean expression, the truth table, a printout of your LogicWorks simulation, and your layout/wiring diagram for the design that uses two ICs and NAND gates.