Week Four

Week Four


This Week's Overview:

We constructed the "window's" mechanism with our stepping motor and 3D printed gears and actuator. We also created a structure to help demonstrate how our system operates. It is composed of 2 parts: an enclosed box housing our circuit (to indicate that our system is embedded inside the car) and an acrylic box that acts as a gas chamber to help us test our system in a closed environment.


Main Tasks:

1) We changed our air quality sensor to another calibrated sensor: 

Figure 1: MQ-135 Gas Sensor [1].


This MQ-135 measures the CO2 and other organic compounds that are found in the air. As opposed our old MQ-135 sensor, we were able to measure sensible values because it was pre-calibrated. 


We used this equation in the code:


CO2 (ppm) = A x (R_s / R_0)^(-B)


R_s = ((V_in - V_out) / V_out) / RL


where R_s: sensor resistance at a certain gas level

           R_0: sensor resistance in clean air

           A and B: calibration constants


All of these values can be found on the component's data sheet.


2) We were able to make our code run on the Raspberry Pi Pico 2 W automatically when it connects to a power source.


-  We achieved this by naming our source code (main.py).


3) We were able to create a mechanism that simulates a car's window:

- We received our 3D printed gears and actuator to construct the mechanism:



- The actuator and the rack were tightly held together, so we had to loosen them up with a hair dryer so that the rack can slide through the mechanism without an excessive of friction.

- We constructed an acrylic box (to simulate a gas chamber that we can use to test our system in an enclosed environment). The mechanism above and our stepping motor were then secured inside the box. The acrylic box's lid was partially secured to simulate the window.


- We faced difficulty trying to align the motor with the mechanism, but we measured and cut pieces of cardboard to secure the motor to the box.


4) We constructed a structure composed of 2 parts to aid in our demonstration: 

a) To indicate that this system is meant to be embedded inside a car, we placed our circuit in an enclosed box and fed our sensors' wires through the small openings on top of the box. Then, we secured the sensors to the top with tape to stop them from moving around.

b) We placed the acrylic box on top of the box with our circuit to create a gas chamber that tests our sensors in an enclosed environment.



5) We tested our code with this new structure and it worked as intended. 



Next steps:

- Creating our poster for the bench bench inspection



References:

[1]     A-Z Delivery, "MQ-135 Gas sensor air quality sensor,"  A-Z Delivery. [Online]. Available: https://www.az-delivery.uk/products/mq-135-gas-sensor-modul. [Accessed: Feb. 20, 2025].


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