Computer Science and Mechatronics Department Electrical and Electronics Engineering Partial 1 – Lab assignment 3: Kirchhoff and Ohm’s Laws NAME: Salvador Monsalvo Paz ID: A01705019 NAME: Juan Pablo Domínguez Souza ID: A01704911 NAME: Alan Santoyo Mares ID: A01209626 NAME: Santiago Miranda Suarez ID: A01703250 INSTRUCTIONS: In groups of 4 people, work on this assignment. See the “People” section in Canvas to find out who your teammates are for this assignment. Whenever asked, write down your procedure, including formulas, diagrams and calculations, as well as the corresponding units in the final answers, otherwise your work will not be considered. ATTENTION! Points will be deducted in the following situations: a) b) c) d) If procedure is not included in the required situations (analysis and calculations) If electric diagrams are not included (when required) If COMPLETE data (name, ID, date, etc.) is not included above If corresponding units are not included in the answers OBJECTIVE: to design and implement a circuit that illustrates Kirchhoff and Ohm’s Laws. Part 1 - Design LEDs (acronym for Light Emitting Diode; read as “El-E-Dee”) are electronic components capable of emitting energy in form of light when a current is passed through their terminals. LEDs exist in various colors, each with particular electrical characteristics. Red LEDs, for example, have an operating voltage range that goes from 1.8V up to 2.4V, and they can withstand up to 120 mA without being damaged, although a nominal current of 20mA is recommended for normal operation. The brightness of an LED is directly dependent on how much current it draws. However, too much current (i.e., above 120mA), can destroy the diode. If you connect an LED DIRECTLY to a current source, it will try to dissipate as much power as it’s allowed to draw, but it will most likely reduce its lifetime or worst, destroy itself, if current is just too much. Thus, it is important to limit the amount of current flowing across the LED. In order to make an LED work without damage, an alternative is the use of resistors, which will naturally limit the flow of electrons in the circuit and protect the LED from trying to draw too much current, as well as limit the voltage. Consider the circuit shown in figure 1, where a resistor is connected in series with the LED and to a DC voltage source. When the power is on, current starts flowing from the source from the positive pole, and goes through the resistor and the LED, and then goes back to the source and on and on continuously. 1Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering Figure 1. Protection circuit to power an LED. 1.1. Ideal values Considering that the circuit in figure 1 is powered by a 9V power supply, compute the value of the resistor R1 to make the LED light with a voltage drop of 2V (which is within its specified operating range), and run with the recommended nominal current. Use Kirchhoff’s and Ohm’s Laws as needed. Draw the circuit below and also CLEARLY annotate your calculations (this, is, literally, all your calculations, equations and explanations must be clear). INCLUDE explanations and/or comments as necessary. Write down the final values in the corresponding blanks. Calculations to find the value of the protection resistor Include your calculations and explanations here (10 pts.): at first place to find the voltage, we have to use kirchoof´s voltage law, in order to find the voltage drop in the resistor we need to use the 9V from the source and 2V that are the ones that our LED will need: 9V-2V=7V The 7V are the ones that will be in the resistor, as they´re connected in series, the current will be the same in the LED and in the resistor so we need to use 20 mA as it said in the problem explanation. R = V /I R = 7v/0.02A = 350 Ohms Theoretical value of R1 (2 pts.): 350 ohms Theoretical LED voltage ( V L ) (2 pts.): 2 volts Theoretical current value ( I ) (2 pts.) : 20 mA 2Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering Part 2 – Simulation and Implementation 2.1. Simulating the circuit Use the Falstad simulator to simulate the circuit shown in figure 1. If everything is properly set, you should see the current through the LED to be around 20mA, as desired. Paste a picture of the simulation clearly showing the current through the LED (5 pts.): 3Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering 2.2. “Implementing” the circuit Now use Tinkercad to build the circuit in figure 1, using the values computed in part 1. Once you have it correctly working, your job is to validate Kirchhoff’s Laws by doing some measurements (if everything is correct, the amount of current that the circuit is demanding should be about 20mA). IMPORTANT: use the 9V battery from the available power devices to power the circuit. Please follow the pinout in fig. 2 to properly connect the LED. Figure 2. LED pinout. IMPORTANT: remember to follow these considerations, so everything runs smoothly: ● Build your circuit before you connect to the power supply ● Configure the power supply. Set the voltage to the required value, and set the current limit to 0.1A. ● Make sure that the power supply is OFF before connecting it to your circuit. ● Connect the power supply to your circuit, and turn it ON. If everything is working properly, you should see in the power supply the amount of current being demanded by the circuit, which in this case should be approximately 20mA, as desired. Also, you should see the LED light. 4Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering (5 pts.) Take a screenshot of your circuit, CLEARLY showing every component (text must be legible): 2.3. Measurements Now, it is time to measure the real values in the circuit. For this, connect the multimeter to measure the voltage drop in the LED and the current being drawn by it. Take a screenshot of the measurements and write down the measured value. (4 pts.) Picture of the measurement (voltage in the LED): (1 pts.) Real LED voltage: 2.07V Read the current value and write it down. (5 pts.) Picture of the measurement (current through the LED): 5Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering (1 pts.) Real LED current: 19.7mA Part 2 – Error calculation 2.1 In real implementations, normally there will be some differences when comparing the theoretical values against the real values observed. To know to what extent, please fill in the following table computing the percentage error of the values in the LED. (6 pts) Include your calculations for both errors (voltage and current): Voltage Current THEORETICAL (2 pts) 2V 20mA REAL (2 pts) 2.07V 19.7mA Error (%)(4 pts) 3.3% 1.52% Part 3 – Reflection 3.1 Answer the following reflection questions a) (6 pts.) Do the values obtained in the theoretical calculations equal the values observed in the implementation? Why? Explain giving at least 3 different reasons for such differences, if any. The values obtained in theoretical and implementation are not equal, there is a 3.5% difference between both calculations produced by the precision capacity of measuring instruments and the appreciation errors in an experimental practice. Systematic errors in components such as the resistors may affect the overall calculations. 6Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering b) What is the minimum value of the resistor that you have to use, so the LED does not surpass the maximum current, according to the values given in the description at the beginning of this document? Please include your calculations and explanation, and 4 pictures of the simulation in Tinkercad, according to the following tables: Calculations to find the minimum value of the resistance, so the LED does not break Include your calculations and explanations here to find the minimum value of the resistance (8 pts.): In order to get the minimum value that our resistance can have, we need to use the minimum voltage where a LED can work (1.8v) and the minimum current (20mA). 90 Ohms is the minimum value for our resistance, meaning that is the value where our LED will break. Pictures of 4 simulations in Tinkercad, measuring (showing) both the voltage and the current in the LED (CONNECT TWO MULTIMETERS, one for each variable) Picture 1, using the ideal, nominal value of the resistor (2 pts.). Value of resistor used (1 pt.): Picture 2, using a resistor with value above the nominal value of the resistor (2 pts.). Value of resistor used (1 pt.): _____ R= 350 ohms R= 450 ohms 7Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering Picture 3, using a resistor with value below the nominal value of the resistor, but above the minimum value (2 pts.). Value of resistor used (1 pt.): _____ Picture 4, using a resistor with the minimum value, when the LED breaks (2 pts.). Value of resistor used (1 pt.): _____ R= 50 ohms R= 250 ohms What can you conclude from these 4 values in the resistor with respect to the effect in the LED, in terms of the current and voltage observed? Broadly explain (6 pts.): the different values that the resistance adopt affect directly in the LED behaviour, the less resistance the more current crossing to the component, the same happens with voltage. So, as a conclusion, the less resistance we have, the more voltage and current the LED will have to take and eventually it will break when the resistance is nearly 50 ohms or less. c) When the circuit is running, the voltage source is delivering power to the electrical components found in it. In turn, each passive component uses (dissipates) an amount of this power. Using the REAL values measured in number 3, compute the power dissipated through the LED in form of heat and light (annotate as necessary filling in the table with your calculations): Power= Current*Voltaje CALCULATIONS and explanations for the power in the LED Theoretical Power Real Power % Error Include your calculations and Include your calculations and Include your calculations and explanations here (3 pts.): explanations here: (3 pts.) explanations here: (3 pts.) 8Roberto Hernández – robertohj@gmail.com Computer Science and Mechatronics Department Electrical and Electronics Engineering The Theoretical Power was obtained with calculations, using the values of 2 Volts and 20 mA, we get 40 mW of power. P=0.020*2=0.04 The Real Power was obtained with simulations, using the values of 2.07 Volts and 19.7 mA, we get 40 mW of power. P=0.0197*2.07=0.040779 for the error we use the next formula: Theoretical Power (1 pts.): 40mW Real Power (1 pts.): 40mW % Error (1 pts.): 1.91% [(0.040779-0.04)/0.040779] *100 = 1.91% Part 4 – Conclusions Write your conclusions on this experiment, elaborating (explaining in detail) on technical and practical aspects, as well as teamwork (6 pts.): As we begin to study new and more complex topics we come to the conclusion that we are just seeing the basics, this is what we need to understand in order to solve harder problems and have a better understanding of electronics. Kirchhof’s law is very useful, and thus requires a deep understanding to use it, we tried and for the most part were successful. As a team we worked as closely as possible from one another and tried to do this practice as was told, we managed to communicate and execute our report. Using the simulators really helps us to put in practices what we’ve seen in class and to make visual connections with the theory. One of the biggest challenges was to find the resistor value, we needed more reading comprehension because we fought a lot to find what values we should use in order to find the correct value for the resistance, after that everything was quite easy, since we already notice what values we have to use. put them in the simulations was rutinary and getting the results wasn't complex. 9Roberto Hernández – robertohj@gmail.com
