CSC 405 Lab 1 - Building a Simple Combinatorial Circuit

1. CSC 405 Lab 1 - Building a Simple Combinatorial Circuit In this laboratory exercise you will learn about the layout of some small-scale integrated circuits (SSI ICs), light-emitting diodes (LEDs), and the electronic experimenter’s socket board (breadboard) as you design and build a simple combinational circuit. 1. First lets get familiar with the breadboard. The bread board has many strips of metal (copper usually) which run underneath the board. The metal strips are laid out as shown below. Bottom View Top View These strips connect the holes on the top of the board. This makes it easy to connect components together to build circuits. To use the bread board, the legs of components are placed in the holes (the sockets). The holes are made so that they will hold the component in place. Each hole is connected to one of the metal strips running underneath the board. Each wire forms a node. A node is a point in a circuit where two components are connected. Connections between different components are formed by putting their legs in a common node. On the bread board, a node is the row of holes that are connected by the strip of metal underneath. The long top and bottom row of holes are usually used for power supply connections. On some boards these long strips run the entire length of the board. On others they only run halfway. The rest of the circuit is built by placing components and connecting them together with jumper wires. For chips with many legs (ICs), place them in the middle of the board so that half of the legs are on one side of the middle line and half are on the other side. 2. Now we will examine the light-emitting diode (LED). The important thing to remember about diodes (including LEDs) is that current can only flow in one direction. When the proper voltage is applied to the leads of the LED it will glow. To make an LED work, you need a voltage supply and a resistor. If you try to use an LED without a resistor, you will probably burn out the LED. The LED has very little resistance so large amounts of current will try to flow through it unless you limit the current with a resistor. As a test we will make our LED light up using the simple circuit below. Look closely at the leads of the LED. The longer lead is the one that must be connected to the positive side of the power source.

2. A B A AND B 0 0 0 1 1 0 1 1 A B A OR B 0 0 0 1 1 0 1 1 A NOT A 0 1 3. Next we will identify the integrated circuits (ICs) used in this exercise. We will be using TTL (transistor-transistor logic) ICs containing NOT gates (7406), AND gates (7408) and OR gates (7432). Your particular ICs may include other letters or numbers within the 7400 series number, such as 74LS06 or 74F32. 7408 7432 7406 Looking down at the top of an IC, find the end with the notch (or possibly a small dot) and place this end to the left. The gates inside the IC are connected to the IC pins (legs) as shown in the diagrams above. In addition to the gate connections each IC will have connections for power (VCC) and ground (GND). If you are unfamiliar with the proper use of the breadboard or how the ICs should be placed on the breadboard please ask the lab instructor for help. 4. Insert each of the ICs into the breadboard leaving at least 5 columns of holes between ICs. Choose one of the long rows at the top as your +5V line and one of the long rows on the bottom as your ground line. Connect each VCC pin to the +5V line and each GND pin to the ground line. 5. Test one of the gates in each IC by connecting the gate output to the positive lead of the LED circuit and then connecting +5V or ground to the gate inputs. Verify the functions of the NOT, OR and AND by recording your observations in the tables below. +5V or Gnd +5V or Gnd Connect gate inputs to +5 volts or to the ground line. +5 V = true Gnd = false 330 Ohms

3. BC A 00 01 11 10 0 1 A B C F(A,B,C) Your Circuit 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 6. Simplify the following Boolean expression: F(A,B,C) = ABC’ + AB’ + A’BC + ABC + A’B’C’ F(A,B,C) = 7. Draw the circuit diagram for the simplified Boolean expression. C A B 8. Implement your circuit using the necessary ICs and test it to verify your design. Did your circuit output match the function for F(A,B,C) for all values of A, B and C? ____________ Discuss your results ________________ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ _________________________________ Ref: Notes on breadboards and LEDs from http://www.proaxis.com/~iguanalabs/