Electronic Digit I

ELECTRONIC DIGIT I

LAB 3: DECODERS

OBJECTIVES

1. To expose the student with one of the combinational logic circuits application. 2. To understand the operation of decoder. 3. To design and construct a type of decoder.

EQUIPMENTS/COMPONENTS

 DC power supply capable of 5V DC output  Pattern generator  Multimeter  Logic Gate ICs : 7404 (1pc), 7432 (2pc), 7448 (1pc), 7490 (1pc)  Seven Segment Display (1pc)  Resistors : 330Ω (1pc)  Switches (4pc)

INTRODUCTION

A decoder is a circuit that creates an output based on the binary states of a given input. It is used in many applications. One example is in computers for input/output selection. Computers must communicate with a variety of external devices (e.g. printers, disk drives, modem etc.) by sending and/or receiving data through what is known as input/output ports. In this case, a decoder is used to select the I/O port as determined by the computer so that data can be sent or received from a specific external device. Other than that, systems such as digital watches, calculators and cellular phones use decoders for multi-segment display. In this case, decoders are needed in these systems to decode the binary data into the multi-segment data to drive the display.

In this session, you will first create a normal BCD counter using a BCD-to-seven segment display and its decoder by using existing logic ICs. The display should show the following :

The second part will enhance your decoding system and let you study further the addition of other decoding ICs into your construction.

KOLEJ UNIVERSITI KEJURUTERAAN UTARA MALAYSIA ELECTRONIC DIGIT I

PROCEDURE

Part A

In this lab you will experiment with a decoder and associated hardware to derive a BCD counter onto a seven-segment LED display. Your job for this lab is to design and test a circuit to convert a 4-bit BCD signal into a 7-bit control signal according to the following figure:

Fig Figure 3.1 : BCD counter schematic diagram

1. Construct the circuit in Figure 3.1 onto your breadboard. From the output of your 7448 BCD-to-7 segment decode, wire the pins to the 7 seven segment display as shown in Figure 3.2 below.

Figure 3.2 : 7 Segment display schematic diagram

2. Study the light emitted on every value shown based from the decoder connector. Fill in the table 3.1.

Table 3.1 : The 7-segment output truth table

Part B

1. Instead of using the 7448 BCD decoder, create your own combinational logic decoder that will only display the following counting sequence.

2. Prepare the necessary steps using the K-map technique and obtain the Boolean equation. Take note to consider unwanted values as don’t care states and redundant for any current values.

3. Construct your design onto the breadboard. Use the switches first as your inputs. Verify with your instructor on your design.

4. Replace your input switches with the 7490 decade counter IC. Verify the counting sequence with your instructor. Take note to remember where your inputs are. This is important when wiring between your two systems.

5. For your experiment data sheet, submit your Part B :

(a) Truth table (b) K-Map (c) Schematic Design

CAUTION !!! Marks will be deducted for messy submissions.

REPORT REQUIREMENT

The lab report should include the following:

1. Summary of each experiment done. 2. Results of each experiment. 3. Discussions on each operation. 4. For Part B, include your K-Map table, the simplified Boolean equation, include the circuit diagram and the truth table. 5. Remarks on any possible failures and measures done to overcome this problem. 6. Conclusion for the experiments.

EKT 121 DIGITAL ELECTRONICS I EXPERIMENT DATA SHEET

NAME :______METRIC NO.:______COURSE :______LAB EXPERIMENT : ______

Part A

Table 3.1 : The 7-segment output truth table

Circuit construction verification

Instructor’s signature : ______

Part B

1. Attach together with this experiment sheet are your

Counting sequence truth table CAUTION !!! K-Map Marks will be deducted for messy submissions Schematic Design

2. Counting sequence using switches.

Is the circuit construction OK? ______

Instructor’s signature :______

3. Counting sequence using the 7490 decade counter.

Is the circuit construction OK? ______

Instructor’s signature :______

KOLEJ UNIVERSITI KEJURUTERAAN UTARA MALAYSIA