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?
As we know, when enough current passes through a circuit and into a light emitting diode, that diode will light up. However, if the current passing through the diode is too much (the voltage at the diode is too much), it will cause the diode to overheat or get destroyed. Thus, we use resistors in step 1 and 2 so that they may control or limit the current passing through the diodes to prevent any damage to the diodes.
B. How do you recognize 1's and 0's using the circuit you built in Step 3? Give a brief explanation.
There will be a junction between the two diodes which will serve as a "fork in the road" where current either passes through the top or the bottom; and then with a probe on the junction, you will be able to recognize 1's and 0's. When the probe is set to logic 1, which is a "high", current passes through the top, causing the diode at the top to light up. When the probe is set to logic 0, which is a low, current passes through the bottom, causing the diode at the bottom to light up. By connecting or setting the probe to different parts of the circuit, you will be able to know whether that part of the circuit is emitting a 1 signal or a 0 signal depending on which diode lights 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 resistor is there again to control the current passing through the circuit. In this case, it slows down the time it takes up to "fill up" the capacitor because it lessens the current that passes through the capacitor. The capacitor, on the other hand, is like a pail. When current goes to the capacitor, it charges or fills up. And then when it reaches a certain point, it suddenly discharges all the electricity that is has stored (amounts depending on what kind of capacitor). This process of charging up and then suddenly discharging current continues on and on and produces an oscillating or alternating effect of 1's and 0's. Therefor we can say that the combination of the resistor and capacitor has the ability to control the speed of change from 1 to 0, also affecting the current that passes through the chip. (see #4)
D. How does the 555 run an "oscillator"? Give a brief explanation.
4. The 555 is a chip that changes state at 1/3 and 2/3 of the voltage. If the pin 2 goes to a voltage of less than 1/3, then this will signal a high to pin 3. If the pin 6 goes to a voltage of more than 2/3, then this will signal a low to pin 3. With the help of the capacitor, the chip will then signal a high and then a low alternately, producing an oscillating effect that will make the diodes blink alternately. (see #2)
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Laboratory Report 2 - Counting Up and Down
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A. Operating the 7490 counter
The 7490 IC is what we like to call a "counting chip," simply because it is used for counting. It "counts" by using the binary system (not our usual decimal system). It does this by sending out signals from four pins, each corresponding to a certain digit. When a pin sends out a HI signal, it effectively transmits a "1" and when it sends a LOW signal, it transmits a "0." The four pins (in order from right to left, when represented in binary) are pin 12, pin 9, pin 8, and pin 11. So if pin 8 outputs a HI, pin 9 outputs a LOW, pin 11 outputs a LOW and pin 12 outputs a LOW, we end up with the chip transmitting "0100" (or simply "4" in decimal).
Pins 2 and 3 on the 7490 chip are used as a sort of "reset to 0" trigger. Whenever a HI signal is sent to them, all output pins are automatically assigned to send a LOW signal (hence, starting over from "0"). Pins 6 and 7, on the other hand, are used as a "reset to 9" trigger. So, whenever a HI signal is sent to them, a signal "1001" is sent out (hence, sending a "9"). The 7490 IC is actually a "dual flip-flop," or a counter with two parts (A and BCD). This means that pin 1 had to be connected to pin 12, because the second flip-flop (BCD) will only count if pin 1 detects a signal. This signal comes from pin 12, which is the first flip-flop.
B. Operating the 7442 BCD-to-Decimal decoder
The 7442 IC is used to "convert" binary numbers to decimal numbers (well, sort of). It works by receiving four inputs (usually from the 7490, in our case) and "converting" them to their corresponding decimal numbers, represented by specific pins. So if the chip receives a "0001" signal, the pin assigned as "1" will send out a HI signal.
The input pins of the 7442 are pins (from left to right if you want to write it down in binary) 12, 13, 14, and 15. So, let's say pin 12 receives a HI, pin 13 receives a LOW, pin 14 receives a LOW and pin 15 receives a HI. This combination of signals will make the 7442 send a HI signal from the pin assigned to "9" (which is pin 7, by the way). So how does this work with the 7490? Well, since the 7490 sends out FOUR outputs, and the 7442 requires FOUR inputs, all we did was to match the corresponding output to the corresponding input. So, the 7490's pin 12 connects with the 7442's pin 15, 7490's pin 9 connects with 7442's pin 14, and so on.
Since the 7490 IC simply counts, the 7442 IC will also appear to count. Connecting LEDs to corresponding pins, and lining them up in a straight line (in order), will give us "running lights." However, randomizing the placement of the LEDs will give a more random impression.
C. Operating the 7447 seven-segment decoder.
The 7447 IC is also used to "convert" binary numbers into a different set of outputs. The chip has four input pins (which, you would have guessed by now, also connect to the 7490) and 7 output pins, which connect to the "special" LED (which looks like the light on a digital clock).
The input pins of the 7447 are pins 1, 2, 6, and 7 (I forgot the arrangement). But anyway, the way the input pins are connected to the 7490 IC is quite similar to the way the 7442 IC pins are connected to the 7490 IC. Simply match the pins and connect them to each other.
The LED connected to the 7447 lights up the same way a digital clock would. So, let's say the 7447 receives a "0110" signal. It would then send a signal to the LED so that the lights on the LED would form a "6" (which is all lights on, except for the one on the upper-right).
D. How would you explain this experiment to your little brother?
The experiment we conducted consists of four basic parts - a counter, two decoders, and some lights. You can think of the counter (7490), as someone who just counts except no one can understand him. So we need the decoders (7442 & 7447) to "translate" what the counter is saying. Now, each decoder can be seen as a "translator" for the counter, but they translate in different languages. The 7442 IC "translates" for simple running lights, while the 7447 IC "translates" for the special seven-segment LED.
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Laboratory Report 3 - Making Decisions (logic gates / selectors / multiplexer / demultiplexer)
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Overview
The black box is a device that can detect certain input/s and then produce an output of 1 when this happens. This is accomplished by configuring the setup of two chips, the 7400 (a NAND chip) and the 7402 (a NOR chip) in a certain way so that only certain inputs will produce an output of 1. We can "calculate" for this configuration by using the truth table, carno-mapping and other methods.
1. In this case, the black box was configured to detect a 0110, or a 6 through a certain configuration of the NAND and NOR gates.
2. When it detected this number, it gave an output of 1. For all the other numbers, it gave an output of 0.
3. The 4 output pins of the 7490 were connected to the 4 input pins of the black box. While the output pin of the black box was connected to the reset pin of the 7490.
4. What this does is when the 7490 starts to count, it sends corresponding counting outputs to the input of the black box. When the black box detects the input 0110, or a 6, it sends an output of 1 to the reset pin of the 7490. This being done, the counting of the 7490 resets back to 0 and then starts its counting all over again.
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