A. What purpose do the resistors have in the Step 1 & Step 2 diagrams?
This is done so as to limit the current entering or exiting the LED's, to make sure they burn out. An LED will light up if the voltage across it is 1-1.2 volts. The voltage across the probe is 5 volts while the current is about 10 mA, if a 380 W is connected in series with the LED 3.8 volts will go across the resistor leaving 1.2 volts for the LED.
B. How do you recognize 1's and 0's using the circuit you built in Step 3? Give a brief explanation.
Step 3 was to be our logic probe. It would give visual confirmation whether we were at logic 1 or high voltage or logic 0 low voltage, because the LED's would only light up given the specific voltage of 1-1.2 volts. If we were at logic 0 or low voltage only the bottom LED attached to the negative terminal would light up. While if we were at high voltage or logic 1 the LED attached to the positive terminal would 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 resistor and capacitor connected in series act like a simple timer. The capacitor likened to a pail ensures that only a certain amount of current will be discharged. The resistor can be likened to a faucet valve, determining how fast the capacitor will charge. If there is little resistance then the current will be high and the capacitor will take less time to charge, thus making the change from 1 to 0 faster. While if there is large resistance then the current will be low and the capacitor will take longer to charge.
D. How does the 555 run an "oscillator"? Give a brief explanation.
The 555 IC is an oscillator. It separates the voltage into three parts, from pins 4 to 8. If the voltage in pin 2 goes below 1/3 it signals pin 3 to go high then output in pin 7 on the 555 will go high. If the voltage in pin 6 goes above 2/3, pin 3 is at low then the open collector output in pin 7 on the 555 will go low.
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