Lab Report Number 2


Performed by:

Group 8

Abude, Jhoana
Bulanon, Maria Gerardina C.
Raymundo, Tristan Joseph

Introduction

Every Yuletide season, there are remarkable developments to the otherwise plain "series" lights that adorn the Christmas trees, windows and Filipino homes. In the beginning, Christmas lights were just a string of yellow lights connected in series; hence the name "series" lights which it carries now. The "series" lights have evolved into different colors. However, the more remarkable innovation is the variations in the sequence by which the bulbs light up. These are done through integrated circuit (IC) chips and transistors, the first of which is the scope of this experiment.

Materials Used

NE 555 light emitting diodes (LEDs)

7490 counter variable resistor

7442 BCD to decimal decoder capacitor

7400 resistors

7402 breadboard

7447 seven-segment decoder wire

wire stripper

Analysis and Discussion

A. Operating the 7490 Counter

    1. What is the function of pins 2 and 3?

      2. Their function is to reset the count to zero. Together, they are connected to the black box (connection of 7400 and 7402). When a number signal is detected as an output from the black box, it sends a "1" and then the counter is reset to zero.

    2. What happens when any of these pins (2 or 3) are raised to logic "1"?

      3. When both pins are raised to logic "1" then the count is reset to zero. In other words, the outputs all become low or logic "0".

    3. What is the function of pins 6 and 7?

      4. Pins 6 and 7 reset the count to 9. Together, they are connected to the black box. When a number signal is detected as an output from the black box, it sends a "1" and then the counter is reset to nine.

    4. What happens when any of these pins (6 or 7) are raised to logic "1"?

      5. When both pins are raised to logic "1", the count is reset to 9. The outputs then become logic "1", "0", "0", and "1" on pins 12, 9, 8, and 11 respectively.

    5. What is the purpose of connecting pin 1 to pin 12?

      6. The output of pin 14 is pin 12, which is then connected to the second input pin, which is pin 1. This is because the 7490 has two separate flip-flops whose inputs are pins 14 and 1.

      The output of A is the input of B. For B, C and D to "count", there must be input. Thus, the connection of pin 1 and12.

      Note the following:

      7490 7442

      A à 12 15

      B à 9 14

      C à 8 13

      D à 11 12

    6. What are the output pins?

The output pins are pins 12, 9, 8, and 11.

B. Operating the 7442 BCD to decimal decoder

  1. What are the input pins of the 7442?

    2. The input pins are pins 12, 13, 14, and 15.

  2. How did you connect them to the 7490?

    3. The input pins 12, 13, 14, and 15 were connected to pins 11, 8, 9, and 12 of the 7490 respectively.

  3. Describe the behavior of the LEDs connected to the outputs of the 7442?

The light emitting diodes (LEDs) lit up in sequential order. Only one LED, at any time, was lighted. If the LEDs are arranged in a straight line, they light one after the other. Similarly, if arranged alternately, they light alternately.

C. Operating the 7447 seven-segment decoder

  1. What are the input pins of the 7447?

    2. The input pins are 1, 2, 6, and 7.

  2. How did you connect them to the 7490?

    3. The input pins 1, 2, 6, and 7 were connected to the output pins 9, 8, 11 and 12 of the 7490 respectively.

  3. Describe the behavior of the LEDs connected to the outputs of the 7447.

The LEDs connected to the output pins of the 7447 lighted up in a seemingly random order. This is because the output of the 7447 is connected to a light display (which lights up as it counts from 0 to 9). The LEDs would light up in a seemingly random order because of the linear positioning of the LEDs as compared to the lights of the seven-segment display.

D. General Observations

If you were to describe the experiment to your 12-year-old younger brother or sister, or to your mother, how would your description read?

Imagine that you are Harry Potter in your second year at Hogwarts School of Wizards. You are also the 7442 chip. NE555 is Headmaster Dumbledore. He tells the other chips, students of the school, when to "change" magic words (signals). 7490 is Potions Professor Snape who gets signals or "commands" from Dumbledore and he gives out 4 "commands" (output pins). The "commands" (signals) are given in a specific order (the order is in binary count). This combination of "commands" (signals) produces a "spell" which are then passed to you, Harry. Depending on the "spell" taught to you, you can produce only one potion (output of logic "1" on only one of 7442’s output pins). Now you can light up ten lights in succession as you speak a "command" (signal) to them. You can see a display (seven-segment LED) light up as well as you count from 0 to 9. [In parenthesis are comments which maybe a little too technical for a 12-year-old to understand.]