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Laboratory Report 1 - Who are 1's and 0's anyway?
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A. What purpose do the resistors have in the Step 1 & Step 2 diagrams?
The purpose of the resistors in the Step 1 and Step 2 diagrams are to lower the current passing through the LED such that it is within the safe amount of current. This is to done in order to prevent the LED from burning up due to excessive current. We did burn up one bulb during the course of the experiment. It glowed intensely and heated up for almost half a minute before dying out. We discovered it to have been caused by misconnections on our part.
B. How do you recognize 1's and 0's using the circuit you built in Step 3? Give a brief explanation.
The LED that lights up when the probe is connected to a positive source is the logic 1 while the LED that lights up when the probe is connected to a ground is the logic 0. The connection of the probe in between the two LED setups plays an important role in determining the two logics. Upon connection to a positive source, the current will flow from it to the LED circuit closest to the negative end. This will cause logic 1, the one close to the ground, to light up. Upon connection to a ground, current will pass from the LED circuit connected to the positive end and through the probe, bypassing the other circuit. This will allow the circuit at the positive end, which is logic 0, to light up.
C. What is the purpose of the capacitor and resistor to control the speed of the change from "1" and "0" in the diagram. Give a brief explanation.
The change between 1 and 0 depends on how much the capacitor is filled up at a given instance. The resistor controls the speed at which the capacitor is filled up. The higher the rating of the resistor, the slower the capacitor gets filled up, thereby changing the rate at which 1 and 0 change. Further enhancement activities regarding manipulation of pin 7 could not be performed as desired. This was due to extensive technical difficulties involving human and equipment error
D. How does the 555 run an "oscillator"? Give a brief explanation.
The ne555 runs an oscillator in the following manner: A given current runs through the circuit and fills up the capacitor. Pins 6 and 2 monitor how much the capacitor is filled up. When pin 2 detects the capacitor to be at 1/3 charge, it sets pin 3 to a high signal and sets pin 7 to non-conduction. This will set the probe to ground and cause logic 1 LED to light up. Upon reaching 2/3s, pin 6 will set pin 3 to low and allow pin 7 to conduct. This will set the probe to positive and cause the logic 0 LED to light up. Once the capacitor fills up, it expends its charge and goes back to 1. The process then repeats itself. .
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Laboratory Report 2 - Counting Up and Down
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Part A. Operating the 7490 counter
- The function of pins 2 and 3 of the 7490 counter are to reset it to 0. Normally, this is set to 0, or grounded. This is usually true unless there is a special need to reset the counter at a given condition.
- When any of the pins are set to 1, the 7490 counter is forcibly reset to 0. this will cause the 7490 chip’s output to all emit 0’s.
- The function of pins 6 and 7 is to reset the counter to 9. Normally, this is also set to 0, or grounded. Unless, of course, there is a need to control the counter at a certain condition.
- When any of the pins are set to 1, the 7490 counter is set to 9 and the output pins will emit 1, 0, 0, 1 respectively. This is the binary equivalent of the decimal value 9.
- Pin 1 emits the signal A, from which B,C and D are dependent. The purpose of connecting pin 1 to pin 12 is to loop back the signal A to pin 12 in order to produce signals B, C, and D.
- The output pins of the 7490 counter are pins 1, 8, 9, and 11.
Part B. Operating the 7442 BCD-to-decimal decoder.
- The input pins of the 7442 BCD-to-decimal decoder are pins 15, 14, 13 , and 12.
- They are connected in the respective manner: A to A, B to B, C to C, and D to D. The signals match up respectively.
- The LEDs lighted up in sequence one by one, following the count of the 7490. On signal 0001, the first LED lit up, on 0010, the second LED lit up, and so on and so forth. Once it reached the last bulb, the first light lit up anew and the entire cycle repeated.
Part C. Operating the 7447 seven-segment decoder.
- The input pins of the 7447 seven-segment decoder are pins 1, 2, 6, and 7.
- Linking up the 7447 with the rest of the circuit is as follows: Another connection is made from the output of the 7490 that goes to the 7442. This connection is then directed to the 7447. This is done so that the counter signal from the 7490 can be used by the 7447.
- When configured correctly, the LED connected to the 7447 was able to display the position of the currently lit bulb in decimal form. It was a bit troublesome trying to find the correct pins that corresponded with the correct segment. It was further complicated by human error.
Part D. General Observations.
This experiment is about making the little light bulbs light up in a certain order. This is made possible by a chip that can actually perform simple counting. Another chip translates the counting of the other chip lights up the appropriate bulb.
Even better, the whole setup can be made to cycle not only after completing the entire set of bulbs, but also after a certain number of bulbs have lit. Another group of chips working together produces a signal that tells the counting chip to "reset" back to 0 once a given number is met.
A little display can also tell you, in numbers, the position of the bulb that is currently lighting up. This is made possible by another chip that deciphers the signals of the counting chip into the format understood by the numerical display and passes it to the said display for the number to be shown.
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