A. What purpose do the resistors have in the Step 1 & Step 2 diagrams?
Resistors control the flow of current. The resistors in step 1 and step 2 limit the current that flows to the diodes. This is necessary for the diode to function properly and light up. If no resistors were included in the circuit, we will not be able to control the current entering the diode making it possible for it to break.
Let us further explain resistors by introducing Ohm's law. Ohm's law states that the voltage across a resistor is directly proportional to the current flowing through it (V=IR). Therefore, if the voltage is high, then the current running though the resistor is also high (and vice versa). This also tells us that resistance is indirectly proportional to current. Therefore, if the resistance of a specific resistor is high, then the current flowing though it is low (and vice versa).
B. How do you recognize 1's and 0's using the circuit you built in Step 3? Give a brief explanation.
Since the circuit on step 3 is designed where the top LED is connected to the power source and the bottom LED is connected to ground (with both having resistors), we can use this as a visual logic probe. We connect one end of a strip wire in between the two resistors and LEDs. The other end will be our probe tip. When the probe tip touches a 0, the current will only pass through the top LED. When the probe tip touches a 1, the current will pass through the lower LED. Therefore, if the top LED lights, it is a 1; and if the bottom LED lights, it is a 0.
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.
Like mentioned earlier, resistors limit the current that flows through a circuit. On the other hand, capacitors store up current. To better explain the purpose of a capacitor and a resistor, let us use a simple analog. Imaging a bucket (capacitor) being filled up with water (current) at a certain speed (resistor) then being drained. The capacitor acts like a storage. Current continuously flows to the capacitor causing it to fill up. The resistor, on the other hand, controls the speed of current that flows to the resistor. The smaller the resistance, the faster the flow of current through the resistor, into the capacitor and out of it. This makes the speed of the change from 1 to 0 faster. (and vice versa)
D. How does the 555 run an "oscillator"? Give a brief explanation.
The capacitor starts out with no voltage across it. Then, the capacitor is fed current through the resistors. When pin 6 on the 555 senses that the voltage on the capacitor reaches two thirds, it will bring pin 3 to low. This also causes the capacitor voltage to start discharging towards zero volts. When the capacitor reaches one third, the value of Vcc (sensed by pin 2 on the 555 chip), pin 3 will switch to high. This will cause the capacitor to start charging up again. The charge/discharge cycle repeats over and over giving us a repetative wave form.
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