Lab_5_Report

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Texas A&M University *

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214

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Electrical Engineering

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Apr 3, 2024

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ECEN 214 – ELECTRIC CIRCUIT THEORY SPRING 2024 Lab 5: Operational Amplifier Application: Electronic Security System Design: Part 2 of 2 Submitted by: Student Name UIN: Section # Group # Sterling Light 232007010 506 N/A Rushi Penki 532002417 TA Name: Nicholas Jeon

Date Performed: Mar 8 th , 2024 I. OBJECTIVE This laboratory aims to increase the group’s understanding of the functionality of an operational amplifier by combining all of the components designed in the previous lab into one interconnected circuit. II. PROCEDURE First, the group constructed every circuit featured in Figure 5.5 from the laboratory manual, starting from the left and moving to the right. To do this, the group first constructed the infrared emitter circuit featured in the first part of Figure 4.10 from Lab 4’s manual. Proceeding down the list in Figure 5.5, the group proceeded to construct the photodetector circuit (Figure 4.12), current to voltage converter (Figure 4.6), signal amplifier (“inverting” diagram in Figure 4.13), and comparator (Figure 4.14). After constructing the circuit, the group tested to ensure that the output voltage was high when the connection between the photodetector and IR emitter was unobstructed, and low when the connection was obstructed. Subsequently, the group constructed the latch, detailed in Figure 5.6. To ensure the functionality of the latch, the output voltage of the latch was measured (in order of the following conditions) after the latch was reset, after the light beam was obstructed, after the obstruction was removed, and after the latch was reset once again. Upon confirming the functionality of the latch, the group constructed the LED circuit featured in Figure 5.7. Using this new circuit, the security system as a whole was tested, and it was found that the system functioned as intended. III. DIFFICULTIES Extensive debugging revealed that there was something wrong with the laboratory equipment utilized during the experiment; either the provided breadboard had subpar connections, or one of the chips issued to the group behaved irregularly. This issue prevented the circuit from functioning properly upon initial construction and forced the group to change chips and swap breadboards during the laboratory. IV. RESULTS All of the measurements recorded during this laboratory were taken to ensure the proper functioning of the circuit, and the process did not require the recording of these measurements. Task 1: In Task 1, after all of the component circuits were constructed and combined, the group measured that the output of the circuit was high when the connection between the emitter and detector was unobstructed and that the output was low when the connection was obstructed. Task 2:

For Task 2, the group made the following measurements: ● After resetting the latch when the emitter/detector connection was unobstructed, the output voltage of the latch was high. ● When the emitter/detector connection was subsequently obstructed, the output voltage of the latch was low. ● After removing the obstruction from the previous measurement, the output voltage of the latch remained low. ● Once the latch was reset a second time, the output voltage of the latch reverted to high. Task 3: Once the LEDs were installed, the group ensured that the green light was illuminated in situations where the emitter/detector connection had not been obstructed and that the red light was illuminated during and after any obstruction violated the emitter/detector connection. V. DISCUSSION As a whole, the security system functions by detecting if/when an obstruction appears between the infrared emitter and the photodetector. At all times before an obstruction appears, the circuit indicates that everything is as expected, and the green LED is illuminated. Once an obstruction appears and for all times after the appearance of the obstruction before the circuit is reset, the circuit detects that something is amiss and the red LED is illuminated. A brief description of each component of the circuit is as follows. ● The infrared emitter generates infrared light that is detected by the photo emitter. ● The photodetector detects the infrared light that is generated by the infrared emitter. ● The current to voltage converter takes the current generated by the photodetector taking in the infrared emitter’s light and converts it to a proportional voltage value. ● The signal amplifier takes the voltage from the current to the voltage converter and amplifies it by a value determined by the value of the resistors used in the circuit. ● The comparator compares the output voltage of the signal amplifier to a reference voltage. If the signal amplifier’s output voltage is less than the reference voltage, then the comparator’s output voltage is low; if the reference voltage is less than the signal amplifier’s output voltage, then the comparator’s output voltage is high. ● The latch permits the circuit to keep track of whether or not the comparator’s output voltage shifts from high to low; this allows the circuit to “remember” that the connection between the emitter and detector was interrupted until the circuit is manually reset. ● The LED lights serve as a visual indicator of the status of the circuit. If the connection between the emitter and detector has not been interrupted, the green light is illuminated; if at any point the connection is obstructed, the green light is switched off and the red light is switched on until the circuit is manually reset. The emitter circuit’s resistor had a value of 100 Ω to prevent a current of greater than 50 mA. This is to ensure that the emitter is not damaged by an exceedingly large current. The group constructed the current-to-voltage converter using a resistor and operational amplifier. Within this circuit, the infinite gain of the amplifier means that the voltage drop across the resistor is V = IR , allowing the circuit to convert input voltage I to output voltage V . The resistor itself had a value of 470 kΩ to ensure the proper output voltage for the circuit. For the signal amplifier, the group used an inverting amplifier, as the non-inverting amplifier would have reached saturation voltage when working with the input values used during

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this experiment. An amplification factor of -2 was selected, as this was sufficient to raise the output voltage of the current-to-voltage converter to an acceptable value for usage in the rest of the circuit. To achieve an amplification factor of -2, R 1 was chosen to have a resistance value of 1 kΩ, and R 2 was chosen to be 2 kΩ. The comparator’s reference voltage was chosen to be 2.5 V. The reference voltage was connected to the negative terminal of the amplifier, and the input voltage was connected to the positive terminal. With this orientation, the output of the comparator was low when the input voltage was less than the reference voltage, and high when the input voltage was greater than the reference voltage. The group determined that this was the most intuitive way to set up the relationship between the comparator’s inputs and output. The group needed some help putting the circuit together. Extensive debugging revealed that the equipment used was likely faulty in some manner; despite not adjusting the construction, some problems were solved by swapping the chips used for different, identical ones and shifting the circuit elements to an alternative breadboard during the experiment. Beyond that, a careful review of the diagrams included in the laboratory manual, and some assistance from the TA, eventually allowed the group to identify and eliminate all of the issues with the circuit’s construction. After the laboratory, the circuit functioned as intended. Furthermore, during testing, the group did not make note of any missed detections or false alarms, although these occurrences are possible in theory. The most likely cause of false alarms is probably unintentional interruptions in the emitter/detector connection, and the most likely cause of missed detections is insufficient obstruction of the aforementioned connection. The ideal way to fix it would be to improve the quality of the equipment; basic components plugged into a breadboard will function, but not necessarily reliably. However, if limitations existed such that the quality of the equipment itself could not be improved, the best way to limit the issues described above would be to take great care to find the optimal position for both the emitter and detector; this will be the most effective way to limit the chance of both the connection being unintentionally interrupted and the circuit failing to recognize an interruption when it occurs. VI. CONCLUSION All of the measurements taken throughout the experiment indicated that the circuit functioned as intended. The completion of the laboratory resulted in the creation of a circuit that offered a practical benefit, which provided a tangible display of the practical applications of an operational amplifier. VII. APPENDIX

The signed laboratory notebook page is included in the photograph below.