PLTW Engineering Digital Electronics Activity 1.1.6 Component Identification: Digital Worksheet Procedure Combinational Logic 1. Use a switch for the input X and a probe for the output Z. Toggle the switch to complete the truth table shown. Toggle means to change the state of the switch. One “toggle” of the switch changes the state of the switch from low (ground) to high (power). Another toggle of the switch changes the state of the switch from high to low. From analysis of the truth table, why do you think this is called an “INVERTER” gate? 2. Use switches for the inputs X and Y and a probe for the output Z. Toggle the switches to complete the truth table shown. From analysis of the truth table, why do you think this is called an “AND” gate? 3. Use switches for the inputs X and Y and a probe for the output Z. Toggle the switches to complete the truth table shown. From analysis of the truth table, why do you think this is called a “NAND” gate? (NOT AND) © 2021 Project Lead The Way, Inc. 1 PLTW Engineering Digital Electronics 4. Use switches for the inputs X and Y and a probe for the output Z. Toggle the switches to complete the truth table shown. From analysis of the truth table, why do you think this is called an “OR” gate? 5. Use switches for the inputs X and Y and a probe for the output Z. Toggle the switches to complete the truth table shown. From analysis of the truth table, why do you think this is called a “NOR” gate? (NOT OR) 6. Use switches for the inputs X and Y and a probe for the output Z. Toggle the switches to complete the truth table shown. From analysis of the truth table, why do you think this is called an “XOR” gate? (EXCLUSIVE OR) © 2021 Project Lead The Way, Inc. 2 PLTW Engineering Digital Electronics Sequential Logic 7. Using the Circuit Design Software (CDS), enter the 74LS74N test circuit shown. a) Toggle the input T several times until T is low and NOT_Que is low. b) Starting with the switch on GROUND, what happens to output Que when the switch is moved from GROUND to VCC (5V)? This is one toggle of the switch. c) What happens to output Que when the switch is moved from 5V to GROUND? This is one toggle of the switch. d) Toggle the switch one more time. What happened to output Que? What does this tell you about when Que changes (toggles) in relation to when the input at the CLK Changes. (Helpful hint: It might help to cycle through a number of changes to spot this relationship of when Que changes.) e) What is the relationship of D Data in to Que always? f) What is the relationship of Que to NOT_Que always? g) The 74LS74N is called a “flip-flop”. Based on your observations, can you explain the relationship between the D Data in, Que, NOT_Q, and the CLK signal? What does a flip-flop do? © 2021 Project Lead The Way, Inc. 3 PLTW Engineering Digital Electronics Clock Signals (The 555 Timer) 8. Using the Circuit Design Software (CDS), create the three LM555CN test circuits shown below on the same sheet. The 555 Timer Oscillator is one of the most common circuits used in introductory electronics. We will use this design to generate a clock signal in a Random Number Generator (our first full circuit design). We will look more closely at this circuit in the next lesson. In each of the three circuits, the only value that is changed is capacitor C2. a) When C2 is changed from 12μF to 6μF. What happens? b) When C2 is changed from 12μF to 24μF. What happens? © 2021 Project Lead The Way, Inc. 4
