Week 3 Lab Notebook (1)

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Electrical Engineering

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Dec 6, 2023

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Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 Lab 3 Notebook Statement of Purpose ● Anticipate the time-varying voltage output of an AC operational amplifier (op-amp) circuit by analyzing its construction and the characteristics of the input signal. ● Determine the cutoff frequencies and devise filtering circuits with the goal of eliminating undesired electrical signals. ● Comprehend and articulate the functioning principles of photodiodes. ● Generate Bode plots to assess the frequency response of circuits, subsequently drawing comparisons between experimental results and theoretical expectations. ● Apply signal modulation techniques to enhance signals emanating from a photodiode circuit, showcasing an adept utilization of modulation principles for signal improvement. Pre-Lab Calculations 1. Come up with a pair of values of R and C that could be used to make a low-pass filter that will pass through a DC voltage signal while rejecting (>95% attenuation) a 1 kHz interference signal. What is the cutoff frequency for that circuit? Show an equation that describes how you arrived at this answer. 𝑓 𝑐 = 1 2π 𝑅𝐶 Pick R = 1 kΩ and C = 1000 nF Then, 𝑓 𝑐 = 1 2π 𝑅𝐶 = 1 2π (1 𝑥 10 3 ) (1000 𝑥 10 −9 ) = 159 𝐻𝑧 With this cutoff frequency, any frequencies below 159 Hz will be passed and those above 159 Hz will be eliminated. Thus, this pair of resistor and capacitor will be able to reject 1 kHz signal. 2. What is the time constant for the combination of R and C that you chose above? Show an equation that describes how you arrived at this answer. Time constant Г = RC = (1 x 10 3 ) (1000 x 10 -9 ) = 0.001 sec 3. What is a transimpedance amplifier , and how will it be used in this experiment?

Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 A transimpedance amplifier is an electronic device designed to convert a current signal into a voltage signal. It is particularly useful in applications involving photodiodes, where the output is a current proportional to the incident light intensity. The transimpedance amplifier helps convert this current into a voltage, making it easier to process and analyze the calibration curve. Part 1 Two sets of different R and C have been chosen to test out the time constant of an RC circuit. Uncertainty for resistors is 5% and uncertainty for capacitors is 10%. Set 1: R = 1.00 ± 0.05 kΩ and C = 100 ± 10 nF => Г (theo) = RC = 0.0004 sec Set 2: R = 10.0 ± 0.5 kΩ and C = 100 ± 10 nF => Г (theo) = RC = 0.003 sec

Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 R ( kΩ) C (nF) V source (V) V C (V) delta V (V) experimental time constant 1 100 4.88 V -240 mV 5.12 V 200 μs 10 100 4.60 V 560 mV 4.04 V 1800 μs The experimental time constant is determined by the time needed for the voltage to grow ⅔ of it. Set 1 oscilloscope display screen: Observation: the two waves look to overlap if they’re not zoomed in Set 2 oscilloscope display screen: Observation: this set of R and C displays a great example for cutoff frequency

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Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 Part 2 This experiment is trying to create a low pass filter. Our pair of R and C: R = 10.5 ± 0.5 kΩ and C = 100 ± 10 nF The frequency we want to filter out: 159 Hz Obs: It takes us a lot of time to reach the cutoff frequency. Frequency (Hz) Vsource ( V) V out (V) log (Frequency) Gain (dB) 149.512 4.24 3.64 2.174676051 -1.325289459 150.116 4.24 3.68 2.176426984 -1.230360758 151.640 4.24 3.64 2.180813776 -1.325289459 152.744 4.24 3.64 2.18396416 -1.325289459 153.866 4.24 3.64 2.187142664 -1.325289459 155.665 4.24 3.64 2.192190976 -1.325289459 156.596 4.24 3.60 2.194780664 -1.421267117 157.584 4.12 3.52 2.19751212 -1.367091051 158.398 4.20 3.48 2.199749694 -1.633400929 159.694 4.20 3.52 2.203288599 -1.534132538 161.324 4.16 3.52 2.207698982 -1.451013343 164.777 4.16 3.52 2.216896592 -1.451013343 168.417 4.12 3.44 2.226385927 -1.566775469 172.356 4.12 3.36 2.236426407 -1.771158773 175.188 4.12 3.32 2.243504355 -1.875182647 177.786 4.12 3.36 2.249897559 -1.771158773 181.436 4.00 3.32 2.258723463 -1.618438152 183.777 4.00 3.28 2.264291158 -1.723722952 189.567 3.98 3.08 2.277762737 -2.226647111 190.768 3.96 3.00 2.280505527 -2.411478624 192.745 3.96 2.96 2.284983121 -2.528069497 196.456 3.98 2.92 2.293265297 -2.690004413 252.067 3.64 2.44 2.401515993 -3.474231146 280.543 3.48 2.16 2.447999437 -4.142509856 315.675 3.28 1.96 2.499240189 -4.472355447

Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 The Bode Plot is created by plotting log(frequency) on the x-axis, and gain = 20* log (Vout/Vsource) on the y-axis. Part 3 The setup circuit: The cuvette with the solution is placed between the photodiode and the LED light. The photodiode detects the light that shines through the solution in the cuvette. For different concentrations of the solution, it gives out the different voltages. Thus, we make the calibration curve by plotting concentrations (mg/L) vs. voltages (V).

Name: Thao Le Group members: Kaylee Chiou, Payton Steen Experiment: AC Circuits and Light Detection Date: Oct 19, 2023 Since absorbance is proportional to voltage, we don’t have to find absorbance for the calibration curve. Observation: The output voltages are not very consistent when we try to measure the same concentrated solution at different times. Conc. (mg/L) voltage (V) 100 0.78 40 1.82 16 3.11 6.4 3.2 2.56 3.59 Voltage for the blank: 3.64 V Voltage for the unknown: 0.86 V

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