This past week, our team focused on finalizing the capacitive touch design, building the physical construction, and working on software features.
With the capacitive touch sensor, the original grid approach was fundamentally flawed due to how the MPR121 sensor operates. Each time the sensor initializes, it sets a default baseline capacitance, which is significantly influenced by materials in contact with the copper foil tape. To address this, we shifted the design by offsetting the row and column layers and introduced rubber bands for the top layer. However, the rubber bands proved to be too insulating for a finger to trigger a reliable capacitance change. We solved this by wrapping each of the 81 intersection points with small patches of copper foil tape, which made a significant difference and enabled consistent touch registration.
On the physical construction of our project, we needed a container to hold all our electronics, including the Raspberry Pi and MPR121s, and encompass the capacitive touch sensor and numpad. We decided to use a 1/4″ MDF sheet as the base and 1/8″ MDF sheets for the sides and top projection surface. We used a CAD program and a laser cutter at TechSpark to cut out the box joints. We ran into some difficulty because the 1/4″ MDF sheet did not cut easily and caught fire. We put it all together in the woodshop and it is mostly complete. We will have to laser cut holes on the top projection surface for the keypad and the capacitive touch sensor once we test all the components together.
With our software, we created the screen that will display text and give users more information on the game state. We also updated our hints algorithm so that instead of giving the number for a cell, it will first highlight the row, column, and 3×3 box with notes in our side screen telling the user what numbers can potentially go into the requested cell.