COVID-19 Circuit

Design Parameters

For our week one project on bioengineering and electrical engineering, we created a circuit that served as an early warning system for COVID-19 infection. Using switches to simulate inputs on testing for three different COVID-19 symptoms (fever, cough, and low oxygen levels), we created a circuit that output different indications based on how many of these "symptoms" were triggered.

The circuit included green, yellow, and red LEDs. If none of the symptoms were detected, the green LED would light up. If one symptom is detected, the system would light up the yellow LED. If two of the symptoms were detected, the red LED would light up. Detection of all three of the symptoms would sound an audible alarm.

Truth Table and Equation

After learning about truth tables and logic equations, we could accurately create our own truth table and logic equations for our COVID-19 symptom tracker. While our green and alarm logic equations are as simple as possible, our yellow and red logic equations could've been simplified for ease of manufacturing while physically building our circuit.

Complete Design

Fig. 1: Our complete circuit diagram

Fig. 2: Our timer circuit

Circuit Diagram

This diagram show in Figure 1 was created on Tinkercad to digitally mimic what we wanted to create on our breadboards. The section shown in Figure 2 is our timer circuit and the rest of the circuit is our logic circuit.

For our timer circuit, we have two resistors, one of of 2k (top) and one of 300k (bottom), and two capacitors that output a cycle time that is extremely fast in between cycles. The output is powered to the flip flops (this is what also allows for our LEDs to light up at a specific time as well). This is transmitted to the speaker, allowing for it to sound.

Figs. 3 and 4: Our complete circuit schematics

Circuit Schematics

The schematics depicted in Figures 3 and 4 depict our circuit schematics that were generated from Tinkercad. These schematics are for our logic and timing circuits. These schematics helped us to build our circuit in real life because we could easily decipher where we needed different gates, transistors, resistors, etc.

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Video 1: This video showcases our physical alarm system performing its function when it recieves an electrical input. It will later be connected directly to the logic system of the COVID Symptom Tester.

Our alarm system works with two resistors, one of of 2k and one of 300k, and two capacitors that output a charge for three seconds before recharging for another three. In other words, the timer is a cyclic charge of three seconds on and three seconds off. We also used a 555 chip to manage this timing and sound the alarm.

Fig. 6: The diagram we used to build our alarm circuit. We had a couple of issues with the alarm working in real time, but in the end, we were able to make our alarm functional.

Alarm System

For our logic circuit to be fully functional, we needed to start with creating a different circuit for our alarm system. That way, once three symptoms of COVID-19 are detected, that information will be sent to the alarm circuit and the alarm will sound (as shown in Video 1). However, we made sure to have our alarm circuit only work in intervals of three seconds so we could minimize error (ex. someone has been running so their oxygen levels are low).

Fig. 5: Our alarm circuit

Final Circuit

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Video 2: This is our final circuit video. As you can see, we were able to get the logic circuit to work mostly. However, sometimes the yellow light was on when the red light was supposed to be on. Additonally, we also explained in the video how our alarm circuit wasn't connected. All we would've had to do was connect our power wires to positive/negative power and connect one of the gates that triggered the alarm circuit to the alarm/flip flops.

Fig. 7: Our picture of our final circuit. We had to build it on different breadboards for ease of manufacture. However, in retrospect, it would be better for user experience to keep everything on multiple combined breadboards.

We also specifically color coded our circuit to make it as easy as possibly to debug (which was extremely necessary). We also did this because we had the most stock of these particular wires, and they were the longest of the wires, making it easier for us to keep constant with colors instead of having to switch to multiple different colors.

Green: positive

Green with black piece of tape: negative

Green (as well): logic to green LED

Yellow: logic to yellow LED

Orange: logic to red LED

Blue: miscecllaenous

Error Analysis

Even though our design worked perfectly in Tinkcad, we ran into many issues with our logic circuit in the building process. At first, we couldn't figure out why our green light wasn't turning on with the simple NOT and AND gates. After using the multimeter and finding power all throughout the circuit, we figured that starting over was the best way we could fix the problem. However, after taking it apart, we realized that our connections to the positive, negative, and power for our switches were incorrect, meaning a simple switch in wire placement would've fixed our issues. We learned that we should never take things apart to fix problems- we should work as best as we can to find the root of the issue and fix that instead. Additionally, since we took so long to try and fix that one issue, we didn't have a lot of time to test our other components of the logic circuit as well as the timing circuit. And even though our alarm circuit did work, we weren't able to connect it to the circuit system in time. This led to numerous issues within our logic circuit as well as lack of an alarm system. In the future, we will be sure to troubleshoot more efficiently and not start projects anew especially when there's a time constraint.

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