Lab 4

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Texas A&M University *

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214

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Electrical Engineering

Date

Jan 9, 2024

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ECEN 214 - Lab Report Lab Number: 4 Lab Title: Operational Amplifier Application: Electronic Security System (1/2) Purpose/Objectives: In this lab, we created a system that uses an infrared emitter, a photo detector, operation amplifiers, resistors, a comparator, a latch, and light emitting diodes. By creating this system, we are able to familiarize ourselves with each component and determine which components would lead to the desired results. The main goal of this lab is to learn how to use op-amps to do various activities, by making a system that is able to detect an interruption in a light beam and trigger an indication. ● Build a circuit that detects an interruption in a light beam and triggers an indicator.

● Learn the applications of op-amps. Procedure: The purpose of this lab was to understand all the components of the circuit before putting them all together to create an electric security system. This lab is broken down into three parts based on the three components: the IR emitter and detector, the signal voltage amplifier, and the comparator. For the first component, we are going to be testing the emitter and detector. Starting with the emitter, create the circuit in Figure 4.9 and change the value of the resistor while measuring the voltage across the resistor to be able to infer the current that is flowing through the emitter. Next, is working with the detector and essentially repeating the same process as the emitter. Figure 4.9: Emitter and Detector Circuit Built in Lab Figure 4.5: Bench equipment for op-amps positive and negative supply The second component is a signal voltage amplifier that will help amplify the signal to create a noticeable difference between low and high voltages. Create an inverting amplifier as seen in Figure 4.12 with chosen values for the resistors that will provide a high amplification to the circuit with saturating it. Measure the output voltage for different input voltages and display where the saturation occurs. Repeat this process with the non inverting amplifier and explain which one would work best with the detector from the previous task.

Figure 4.12a: Inverting Op-amp Figure 4.12b: Non-Inverting Op-amp The last component is a comparator that takes two output voltages and converts to a digital logic level. Start by creating the circuit in Figure 4.13. The next part is to calculate the value of the two resistors that create a voltage divider that is going into the inverting input of the op amp. Similar to the last task, measure the output voltage for different inputs.

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Figure 4.13: Voltage Comparator in lab. Discussion, Data Tables, and Data Plots: Task 1: IR Emitter and Detector Resistor (Ohms) IR Emitter (V) Resistor Voltage (V) Current (Amps) 100 1.37 3.42 .0342 500 1.23 3.76 .00752 1000 1.20 3.80 .0038 2000 1.17 3.82 .00191 3000 1.16 3.83 .001277 Table 1: IR Emitter Data (as the resistor value increases, the current decreases in the circuit)

Resistor (Ohms) Detector (V) Resistor Voltage (V) 100 4.89 .082 500 4.64 .361 1000 4.35 .820 2000 3.23 1.165 470000 0.565 5.45 Table 2: Detector Data (as the resistance increases, the voltage drop across the resistor increases and the detector decreases) Figure 1: I vs. R (Emitter) Graph Figure 2:I vs. R (Detector) Graph The emitter and detector were approximately two inches apart from each other during the lab that led to these results Obstructions: Rd = 470 kOhms, Re = 100 Ohm Obstruction: 0.892 V, Unobstructed: 5.500 V We decided on a 100 because it produced the highest current allowing it to emit more IR light for the detector. The detector had a 470,000 Ohm resistor because it allowed for the highest voltage to be created with the voltage that was going through the detector. The distance that allowed for our circuit to work was approximately 12 inches apart from one another. The closer the emitter and detector were to one another allowed for a high voltage to be created.

After implementing the op-amp based detector, it allowed for a much greater voltage (8.8 V) to be measured across the resistor, this would help in creating a much more distinct difference between the low and high voltages in the circuit. Task 2: Signal Voltage Amplifier Vin (V) Vout (V) 0.5 0.99 1 1.98 1.25 -2.49 1.5 -2.99 1.75 -3.48 2 -3.54 2.5 -3.54 Table 3: Inverting Op-Amp Data Vin (V) Vout (V) 0.5 1.49 1 2.99 1.25 3.74 1.50 4.20 1.75 4.20 Table 4: Non-inverting Op-Amp Data

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Vout vs. Vin (Inverting Amplifier) Vout vs. Vin (Non inverting Amplifier) For the inverting amplifier, we chose R1 to be 1000 Ohms and R2 to be 2000 Ohms. This is because it gave us a decent gain that would allow for us to get a difference between the highs and the lows. For the non-inverting, we chose R1 as 1000, R2 as 2000, and R3 as 100. With the data provided, it shows that the non inverting circuit was better than the inverting amplifier as it resulted in negative voltage, but also the voltage difference is greater in the non inverting. Task 3: Signal Voltage Amplifier The resistance values we chose for R4 and R5 were 3.3k Ω and 1kΩ resistors respectively. The reasoning for these resistors values is that we want to keep the voltage out (Vr) in between the 1V to 2.5V range. Using the voltage divider equation , and setting Vr equal to 𝑉 𝑟 = 𝑉 𝑖? 𝑅 5 𝑅 4 +𝑅 5 any value between 1V to 2.5V we can get our desired resistors. These values of voltage are chosen to avoid saturation in the comparator. The input voltages to produce a negative 5V the voltage must be lower than 2.5V, while to produce a positive 5V the voltage must be greater than 2.5V. Vout vs. Vin (comparator)

Discussion: To determine what resistor values to use in task 1 (Figure 4.9), we need to understand how the IR emitter and the detector work. By having a higher current in the IR emitter circuit, it allows it to emit more IR light for the detector. Therefore having a lower resistance will result in a higher current in the circuit, leading us to use 100 Ohms. This can be supported by Ohm’s law represented by Equation 2. For the detector, we used the higher given resistor (470,000 Ohms) because it allowed for the highest voltage to be created through the detector. This was found through testing in the lab with a range of resistors. To choose the resistor values in the inverting amplifier, we use Equation 3, where it shows that having a higher R2 value than R1 results in a larger gain. By choosing R1 to be 1000 Ohms and R2 to be 2000 Ohms, we get a decent gain. For non-inverting, we chose the values R1 as 1000, R2 as 2000, and R3 as 100 Ohms for the same reasoning. The detector data in task 1 does fit within the linear range of the op-amp we designed. For Task 3, we want to choose resistor values that result in an output voltage between 1V and 2.5V. To find the resistances, we can use Equation 1 which results in R4 and R5 equalling 3.3kOhms and 1kOhms respectively. Equations: Equation 1, the voltage divider equation, is used to determine the value of resistors needed to avoid saturation in the comparator. Vr represents the intended voltage output, Vin is the voltage through the comparator, and R4 and R5 can be found plugging in resistor values we are given. (1) 𝑉 𝑟 = 𝑉 𝑖? 𝑅 5 𝑅 4 +𝑅 5 Equation 2, Ohm's Law, shows the relationship between voltage and current in a resistor. If solving strictly for current, it can be rearranged to I = V/R. To have a higher current, you can either increase the voltage or decrease the resistance. V = IR (2) Equation 3, op-amp gain equation, where Vout is the output of the op-amp, Vin is the voltage into the op-amp input, R2 is the feedback resistor, and R1 is the resistor connected to the input. (3) 𝑉 ??? 𝑉 𝑖? =− 𝑅 2 𝑅 1 Conclusion: In conclusion, we were able to test all the different components for the system and discuss which option would help us the next lab to be successful in putting the alarm system together. It also helped understand how the components worked and see how they each would

connect to each other in the next lab. We were able to build a circuit that detects an interruption in a light beam and triggers an indicator. Doing so allowed us to learn how to use an op-amp to amplify the voltage or create a voltage comparator. Therefore, both lab goals were met. Signatures:

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