Digital Electronics Lab 2 Instructor: In this lab, we will discuss the fundamentals of digital electronics, and use logic and boolean algebra to design digital circuits. Winter Quarter

Analog Vs. Digital Instructor: First, we will discuss the difference between analog and digital signals. The top signal is an analog signal, and the bottom signal is digital. Note that the analog signal is continuous and can take on any value, while the digital signal can only take on certain discrete values. Winter Quarter

Analog Vs. Digital Analog Continuous Can take on any values in a given range Very susceptible to noise Digital Discrete Can only take on certain values in a given range Can be less susceptible to noise Instructor: An analog signal is continous, and can take on any value in a given range. However, analog signals are very susceptible to noise. A digital signal is discrete, and can only take on certain values in a given range. The advantage of this is that it can be less susceptible to noise. Winter Quarter

The Transistor Basic element of digital electronics Can act like a “switch” Instructor: The basic element of digital electronics is the transistor. It can act like a switch. For this type of transistor, called a bipolar junction transistor, there are three parts, called the base, collector, and emitter. When current flows to the base of the transistor, the “switch” is turned on, allowing current to flow from the collector to the emitter. Winter Quarter

Boolean Algebra Symbolic representation of logic statements Uses many basic arithmetic symbols: +, -, (), etc. Instructor: Boolean Algebra is used to help define digital electronic circuits. It is a symbolic representation of logic statements. Many basic arithmetic symbols, such as plus, minus, and parenthesis are used in boolean algebra. Winter Quarter

Basic Logic Circuits: AND Symbol Boolean Equation Y = A•B Truth Table 1 Y B A Instructor: One basic logic circuit is the AND gate. The truth table shows that the output “Y” will only be “true”, or logical “1” when inputs A and B are “true”. Otherwise the output will be “false” or “0”. The boolean equation is also shown. I means that Y is equal to A AND B. The dot or multiplication symbol means “AND” in boolean algebra. Winter Quarter

Basic Logic Circuits: OR Symbol Boolean Equation Y = A+B Truth Table 1 Y B A Instructor: This is the logical OR symbol. From the truth table, we can see that the output “Y” will be true when any of the inputs A or B are true. The boolean equation shown means that Y is equal to A OR B. The “plus” symbol means “OR” in boolean algebra. Winter Quarter

Basic Logic Circuits: NOT Symbol Boolean Equation _ Y = A Truth Table 1 Y A A Y Instructor: The NOT gate is also called an inverter, in that it inverts the input logic. The output Y is asserted true only when the input A is asserted false. The boolean equation says that Y is equal to NOT A,or Y is equal to A-bar. The bar over the letter means “not” in boolean algebra. Winter Quarter

Basic Logic Circuits: NAND NAND = “not AND” Commonly used to implement other logic circuits Symbol Boolean Equation _____ Y = (A•B) Truth Table 1 Y B A Instructor: The NAND gate means Not AND. It can be used to implement any other logic circuit. The truth table shows that the NAND gate is asserted “false” or “0” only when both inputs are asserted “true”. This is equivalent to taking the output of an AND gate and putting it through a NOT gate. This is reflected in the Boolean equation shown. Winter Quarter

Basic Logic Circuits: NOR NOR = “not OR” Symbol Boolean Equation _____ Y = (A+B) Truth Table 1 Y B A Instructor: The NOR gate means “not OR”. The truth table shows that it asserts a “false” output whenever either A or B is true. This is equivalent to taking the output of an OR gate and putting it through a NOT gate. This is reflected in the Boolean equation shown. Winter Quarter

Integrated Circuits (Chips) A collection of many transistors, resistors, and capacitors on a single silicon wafer The wafer is mounted to a carrier for ease of use and dissipation of heat 1 5 8 4 7 Notches mark pin 1 end or pin 1 of IC (highlighted for clarity) Some ICs are analog because they deal with continuously changing input. Some are digital because they are designed to deal only with binary (two state) inputs. They have various pin counts but 8, 14, 16, 18, 20, 24, 28, 40 are typical for dual-in-line-packages (DIP). The pins are numbered consecutively and counterclockwise around the IC. The pin 1 end or pin 1 itself is marked with a notch. However, there are many package designs for today’s many different ICs. Some are encased in plastic, some ceramic (heat transfer reasons). Surface mount are popular because they save board space, can be easily mounted by machines, and have good heat transfer character. We use standard plastic DIP packaged ICs in the labs. That type is illustrated above. Winter Quarter

Breadboards The “canvas” for laying out a circuit using discrete components (resistors, wires, chips, etc.) Instructor: A breadboard is the canvas a digital designer uses for layout out a circuit using discrete components, such as resistors, wires, and chips. Winter Quarter

Breadboards (continued) Power and ground terminal posts Instructor: The power and ground terminal posts are shown in the top left of the picture. These are connected to an external power supply that provides the needed voltage levels to power the circuit. Winter Quarter

Breadboards (continued) Each small row of holes is electrically connected inside the breadboard Instructor: On the breadboard, each small row of electrically connected inside the breadboard. In the picture, a set of five holes that is covered by the black line is electrically connected. Winter Quarter

Breadboards (continued) Power bus shown in red Ground bus shown in blue These columns of holes are connected electrically Breadboards also have power and ground buses. The power bus is shown in red, and the ground bus is shown in blue. These columns of holes are connected electrically. To provide the proper voltage to them, they must be connected to the power and ground posts. Winter Quarter

Light Emitting Diodes (LED) Function depends on orientation Allows current to flow only one way Illuminates when current is flowing through it Must have current limited by a resistor in series Instructor: Light Emitting Diodes, or LEDs, can be used to show the outputs of the digital circuits. The function of an LED depends on the orientation. They allow current to flow in one direction, and illuminate when current flows through it. They must have current limited by a resistor in series, or an unlimited amount of current will flow through it, burning it out. Winter Quarter

Power MOSFETs Allows control of high current DC loads by low-voltage digital signals With a ‘1’ signal at the gate, current may flow from drain to source. Otherwise, the path is closed Instructor: Power MOSFETs allow control of high current DC loads by low voltage digital signals. MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. This is a transistor build to handle large currents. When a digital “1” is at the gate, current may flow from the drain to the source. Otherwise, the path is closed. Winter Quarter

Laying Out the Circuit Chips “bridge” the gaps Devices in adjacent horizontal rows are connected Make sure power is turned off until circuit is finished! Instructor: When layout out circuits on the breadboard, chips will be used to bridge the gaps, so that each pin has it’s own row of electrically connected holes. Devices in adjacent horizontal rows are connected. Make sure the power is turned off until the circuit is finished. Winter Quarter

Today’s Goals Build digital circuits on your breadboards and determine their function Test the Mystery Circuit Build a circuit to operate a motor with a power MOSFET Winter Quarter