ENG H192: Hands on Labs Lab 2: Digital Electronics Engineering Disciplines Explored: Electrical Introduction Purpose The purpose of this lab is to familiarize students with the fundamentals of digital circuits including Boolean algebra, logic gates, and transistors as well as introduce the use of integrated circuits. Basic Principles This lab write-up will cover the following basic principles:  Digital vs. Analog signals  Advantages of digital logic  Building blocks of digital electronics  Basic logic gates  Boolean algebra  LED’s  Power MOSFETs Lab Experience The lab experience will include experimentation with:  Basic logic gates  Building digital circuits using transistors  Building digital circuits using MOSFETs Fundamentals Digital vs. Analog A digital signal is either on or off whereas an analog signal may take on infinite values. If an analog signal source fades over time, information gets lost in the background noise, just as videotape loses definition over multiple viewings. A digital signal is more robust as its discrete levels (high or low) can be discerned reliably from even poor sources. Analog information is by no means extinct, but it is certainly declining in use. CRT-based televisions, AM/FM radios, and 35mm film all carry analog information. Even now, though, liquid crystal displays, satellite radio, digital cable, and digital cameras are increasing in use. Sound is heard through the vibrations of air molecules. These vibrations are easily converted into electrical signals, which can be transmitted in an FM broadcast. Since audio signals are inherently analog it is efficient to transmit them in the same form. However, there is noise introduced with every analog device (amplifiers, modulators,transmitters, receivers, antennas) that the signal goes through. Noise is variation from the transmitted signal that changes the appearance of the signal. If the noise significantly changes the signal, the unfiltered data being received can be read incorrectly. If the signal was digitally sampled and then converted back to analog at the user end, there could be a lot less noise introduced to the signal. Advantages of Digital Logic Digital electronic devices are much more popular than traditional analog devices because of the added versatility. Digital devices can easily interface with computers, which not only simplifies data manipulation, but also storage and analysis of data. When selected correctly digital devices offer the same precision as an analog counterpart typically with greater reliability and almost always a smaller package Building Blocks of Digital Electronics All computers are built upon the most basic element of digital electronics: the transistor. A transistor can be thought of as a valve, when it is open (or gated) electricity can flow, when it is closed, no electricity can flow. For the circuit shown below, if no current were supplied at the base then the 'gate' would remain closed and no current would flow from 5 volts to ground through the transistor. Since no current could flow through the transistor, no current would be flowing through the resistor and so the output voltage would be equal to 5 volts (binary 1). If current was supplied at the base then the transistor would 'open' and current could flow from 5 volts down to ground through the transistor. This would connect the output line directly to ground (through the transistor) and make the output voltage equal to zero (binary 0). This electrically controlled switch is the basic building block of all digital electronics. Collections of these transistors can be used to create devices called logic gates which are used to manipulate digitally stored numbers. Basic Logic Gates Digital numbers are stored using a system called binary. A binary digit (bit) can be either a 1 or a 0 which also may be referred to as “True” and “False”, respectively. In order to manipulate pairs of True and False values a logic gate is used. Some of these gates are shown below. When a signal or a set of signals enters these gates the output is set according to the logical truth of the signals.AND ORNOT -An AND gate takes in multiple pieces of information and passes on the value true (binary 1) only if all of its inputs were true. The statement Donald Trump is rich AND he is a male is true, however the statement Ohio State University is huge AND worms have sharp fangs is false (binary 0). -An OR gate will set its output as true if either of its inputs are true. The statement ice cream is sweet OR gymnasts have no balance is true because at least one of the statements is true. -A NOT gate simply inverts the truth of the input. This is also called an inverter. NAND and NOR gates act just as like AND and OR gates with a NOT gate attached to the output. NAND gates are especially significant because in most processes they are the simplest two-input gate to construct. The symbols for these gates are shown below. NAND NOR There are several other types of gates such as XOR and XNOR, but these and any other gate can be broken down to simpler gates. In fact, every gate can be implemented using just NAND gates. Truth Tables The following are the truth tables for each of the gates described previously. It is important to note that binary 1 indicates true and binary 0 indicates false, but these do not necessarily correspond to high and low voltage. Some circuits use negative true logic, where a low voltage at an input corresponds to binary 1. Such gates are not used in this lab, however.AB AB000 000100 101010 011111 111AB AB001 001101 100011 010110 110INPUTSOUTPUT0110NOTNANDINPUTSOUTPUTNORINPUTSOUTPUTANDINPUTSOUTPUTORINPUTSOUTPUT Boolean Algebra Simple digital electronic components carry out the functions of Boolean algebra. Boolean algebra is the manipulation of logical statements to determine truth or false. Used in Boolean algebra, are the following three basic symbols: + Represents an OR • Represents an AND To overbar an equation means to NOT it. The Boolean algebraic formula for the basic logic gates are as follows: AND: BAY⋅= or ABY= OR: BAY+= NOT: AY= NAND: ()ABY = NOR: ()BAY += Example: Hydraulic Pump Circuit Turn on the hydraulic pump if and only if the system is enabled, the operator is pressing both palm buttons, the emergency stop button is not pressed and the proximity sensor does not sense probable