Here’s our progress as of week 10!
DAY 1
Wednesday, 17/7/24
Since we planned to start assembling our final prototype already, we decided to discuss the design for our bin’s door and chute (refer to the image below). 
We had some preliminary ideas about what the chute would look like. One of them was a ‘laptop’ shaped contraption, similar to that used in BigBelly bins. As the name suggests, such a chute would be shaped like a laptop opened at 120°, where one side of the ‘laptop’ would have a handle on its exterior for users to pull and open the chute, which would then form an “L” shape where users could then place their trash in, before closing the chute. The diagram below does a better job at illustrating how the ‘laptop’ works 🙂
We all really liked the idea and to confirm the design, we took a site visit to an actual BigBelly bin at Gaia. One of our main objectives of designing such a chute was to prevent users from throwing objects that would interfere with the bin’s ultrasonic distance/height sensors (i.e. long, thin objects), as these would lead to false indicators of the bin being full. Hence, we brought a metal pole down to the BigBelly bin to test whether it would fit in: it didn’t! Hence, our group decided to adopt a similar chute design, modifying it to be a ‘laptop’ instead of the more ‘excavator-bucket’ style used by BigBelly.
After further discussion and consideration of various other components such as the electromagnet, and the necessity of 3D printed parts, we finalised the chute’s design.
^ sketching and ideating
On this day, our ultrasonic transceivers also arrived. We intended to use them as ultrasonic beam break sensors, since we previously faced the issue of infrared beam break sensors being unable to detect transparent objects (Week 8), and based on previous experimentation, we knew that sound waves were not affected by transparent materials, we theorised that it would work. In Week 8 we tried using the existing HC-SR04 as an ultrasonic beam break sensor — taking 2 sensors and placing them across from one another, such that one could act as an emitter, and the other a receiver. However, the sensors were unable to function as hoped, and we theorised that it could be due to the incompatibility of frequencies emitted/received by each HC-SR04. Hence, we purchased ultrasonic transceivers, where a single module could emit and receive signals, instead of the dual sensors on HC-SR04.
Unfortunately, these sensors didn’t work either, as we were unable to connect them to the Arduino properly. Despite our efforts to consult the product’s instruction manual and online sources, it seemed like these sensors were incompatible with the Arduino system (oops!). We revisited the idea of using HC-SR04. This time, using the reflection of sound waves to determine the distance from one side of the bin to another. This is the fixed distance that will always be read when the bin is empty. When the bin is full, an object will block the path of the sound waves, causing a shorter than expected distance to be recorded by the ultrasonic sensor. By using an array of ultrasonic sensors arranged around the bin that emit sound waves in consecutive pulses (i.e. one sensor emitting sound waves at any one time), the bin will be considered full when all sensors detect a shorter/different distance than expected.
To test this, we used our mini prototype cardboard box bin with 1 ultrasonic sensor & the concept worked! The sensor constantly read the expected distance of 20cm as we continually threw trash into the box, until the height of the trash was just below the sensor, where it detected a distance <20cm.
DAY 2
Thursday, 18/7/24
We continued building our actual bin today! It was a tedious few hours of drilling holes in wood, finding appropriate screws & nuts, and attaching the wood to the metal frame, but we managed to do it! In total, we attached 4 pieces of wood – 3 along the sides & 1 for the base. The sturdy wood used was necessary for ensuring that all electrical components and sensors remain in place and do not move around when the bin’s chute is opened/closed/by any force in general, so that their functionalities would not be affected.
We also made a frame for the bin’s door out of the same metal poles, which we intend to leave hollow for the interior of our bin to be visible for presentation.
Lastly, as we were planning to place the load cells onto a sturdier piece of wood for the weight sensor in our final prototype, we decided to disconnect them from our rather flimsy Daiso wooden plank, and attach them to a piece of sturdy wood. This was to make sure that the sturdier material would not deform, thereby leading to more accurate mass readings. This however, was not the final piece of wood that we would be attaching the load cells to, but we did prove that a sturdier surface made for more accurate readings.
DAY 3
Friday, 19/7/24
A chopping board was obtained, which was meant to serve as the new surface for the load cells to be attached to — it was sturdy and fit perfectly in our bin’s base. We began work on transferring the load cells and wiring to the chopping board when disaster struck! One of the wires soldered onto one of the load cells and sealed with putty came loose! We fruitlessly attempted to solder it back, but to no avail. Additionally, we had no extra load cells, which meant that we would have to order new ones, and were unable to work on setting up the finalised load cell on this day.
Since we had to buy new load cells, we also bought an inner bin with appropriate dimensions that fit into our metal frame.
On the camera & software side, we managed to get the Raspberry Pi camera to take a picture with the prototype version of our app on an iOS simulator! The app was also able to display the picture taken after a slight delay (20s).
Additionally, we also 3D printed cases for the ultrasonic sensors to protect them from getting dirty when placed in the bin (by liquid splashes etc.).
