Lab Report Number 3
 Date: February 5, 2002

Performed by:

Group 8

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

Introduction

Have you ever tried thinking about how something is capable of shutting down and restarting on its own, exactly at the time you told it to perform the action? Often, we take for granted the comfort electronic things gives us, like the turning off of a television based on the time we wish for it to turn off. We don’t try to figure out how the process goes on because we tell ourselves that it probably is beyond our comprehension. However, it doesn’t hurt to wonder how things resets and goes back to the very beginning. The following report tries to explain the simple concept of counting and recounting, which has been made abstract by the physical makeup of the things we use.

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

 

Schematic Diagram

Analysis and Discussion
  1. Description of the Black Box

    2. The black box is composed of a NAND chip, 7400 and a NOR chip, 7402 connected in such a way that it (black box) only outputs a "1" when the binary input to it is 0110. Following is the schematic diagram of the connection:

    For the 7400 chip, the input pins are 1 and 2 with its output, pin 3; 4, 5 with its output pin 6; 8, 9 with its output pin 10; and 11, 12 with its output pin 13. Pins 7 and 14 are connected to ground and to +5V, respectively.

    On the other hand, the 7402 chip has input pins 2 and 3 with output at pin 1; 5 and 6 with output at pin 4; 9 and 10 with output at pin 8; and 12 and 13 with output at pin 11. Pins 7 and 14 are at ground and +5V, respectively.

  2. Operation of the Black Box

    3. The function of the black box is to ensure that the 7490 counter resets at a particular number. In the case of the experiment, the black box is so connected such that it resets at 6. Four output pins (12, 9, 8, 11) of the 7490, sends a binary combination to the black box. Our black box was configured so that it sends a "1" when "0", "1", "1", "0" are the inputs to it. In some other applications though, it may be configured to send a "1" for a different binary number.

  3. From the Black Box to the 7490 Counter and Back

    4. The input pins of the black box are pins 1 and 2 of the 7400 and pins 2 and 3 of 7402. These pins are connected to A, B, C and D.

    7490 counter 7442 decoder

    The output of the black box is connected to pins 2 and 3 of the 7490. This is because the function of these pins is to reset the counter.

     

  4. What happens then?

Once the binary input "fed" into it is 0110, the black box sends a "1", signalling for pins 2 and 3 to reset the counter. For a fraction of a moment, the number 6 is displayed in the seven-segment light emitting diode (LED). Afterwards, the count is back to 0.

Also, out of the ten LEDs, only the first six (in linear order) lights up.