Reverse Engineering Project
The purpose of our analysis was to learn how the Casio fx-300 ES Plus calculator functions, as well as understand the mechanical operations of the circuit board and adjoining parts. We started with an understanding of the purpose of the function, which was to output accurate answers in an efficient manner. It was clear to us that the hand-held calculator was designed for portability, but we deemed it necessary to investigate this further, using the reverse engineering process.
Content
We began the disassembly process by physically taking apart the calculator, cataloging each part, and creating an accurate diagram to depict how each component fits together.
The circuit board fits into the back case with the metal plate facing down. Then the key receptor lays on top of the circuit board with the black receptors down. The key/buttons go in between the front shell casing and the silicon key receptor. The display and solar panel should fit into the front shell casing in the designated spaces. Both the back and front casing snap together and the whole calculator is held together by a few screws.
Functional Analysis
The function of the calculator is to output accurate values after an equation is input. To do this, the process begins with the action of pressing the buttons on the face of the calculator. When the button is pressed, the conductive film on the back of the button makes contact with electrodes. This contact activates a flow of electricity from the battery, or solar panel as an alternative power source. This completes the circuit, and the capacitance is read. The electrical signal is then directed through the integrated circuit, where transistors are turned on and off by the electrical impulses to translate the signal into binary. This binary is outputted by the integrated circuit and sent through a second series of transistors to turn lights on and off so that the value is accurately represented on the display.
Structural Analysis
The circuit board fits into the plastic back casing, with the metal plate face down. The circuit board and display are connected by two strips of tape, one is a conductive tape and the other an electrical tape. Then the silicon key membrane lays on top of the circuit board with the black receptors touching the circuit board and its electrodes. The keys of the calculator go in between the front plastic casing and the silicon membrane in their designated spots. The display and solar panel should fit into the front plastic casing, with the glass facing up. Once completed, the two plastic shells snap into place and are screwed together.
Moreover, the plastic casings protect the circuit board and display from being distorted or damaged. They also help keep all of the pieces in place, and its size is small for easy transportation, as it is hand-held.
Materials Analysis
While simply looking at our calculator, we were able to deduce what basic materials it was made out of: plastic, metals, and glass. However, through researching online we were able to identify the specific materials used for the individual parts of our calculator. Below we have listed various parts of our calculator, along with the material used to make each part.
Casing: The protective casing and frame of the calculator are made of acrylonitrile butadiene styrene (ABS), which is an engineering thermoplastic. It is known to be impact resistant, as well as very rigid, and therefore is a perfect polymer to use to protect the circuitry of the calculator. It creates a protective case that can handle hits while still being lightweight.
Battery: The battery used for the calculator is a 1.5 V, LR44 Alkaline battery. For most devices that use single-use batteries, the two primary types of batteries used are alkaline and lithium. Casio used an alkaline battery for their calculator because alkaline batteries are cheaper, and therefore their calculators can be manufactured for less money. Another advantage of alkaline batteries is that they are not as powerful as lithium batteries. This may seem like a downside, but for a device like this calculator, a lithium battery would most likely be too powerful and would damage the circuitry.
Solar panel: The dominant solar panel technology currently is the formation of solar cells using crystalline silicon. This same technology is used for the solar panel in this Casio calculator. These solar cells made up of the crystalline silicon trap solar energy and convert it into electricity to transmit to the LCD display.
Liquid-Crystal Display (LCD) screen: Liquid-crystal display is a very common technology used for screens on any device. LCD technology allows for screens to be much thinner than cathode ray tube technology, and is more energy efficient in comparison to gas plasma and LED displays. The liquid crystals of an LCD screen use backlights, as well as an active matrix display grid to produce an image.
Conductive Rubber Keypad: This part of the calculator connects the plastic buttons to the PCB inside the calculator. The conductive rubber keypad is made of silicone rubber that is durable, yet flexible enough to allow contact between the buttons and the PCB. On the keypad there is conductive film located where each button makes contact. This conductive film is made up of
Wiring: It was not clear whether the wiring inside the calculator was made of aluminum or copper. According to our research the PCB has copper circuitry to connect the capacitors and transistors to the integrated circuit, and then the integrated circuit to the LCD screen. However, we also found that the wiring connecting the battery and solar panel to the PCB may be made of aluminum.
Buttons: The buttons that input the functions for the calculator are made of a soft plastic. Unfortunately the specific plastic used for the buttons could not be identified.
Screws: There are six steel screws used to hold the casing of the calculator together and ensure the circuitry inside the calculator remains protected.
Manufacturing Analysis
Casio's main factory is located in Japan; however, the company has broadened to include factories in Thailand as well. A printed circuit board (PCB) generally consists of four layers, which are heat laminated together into a single layer. The different types of PCB materials used in circuit boards from top to bottom include Silkscreen, Soldermask, Copper and Substrate.
Steps of manufacturing a pcb chip:
Step 1 – The Design
Step 2 – Printing the Design
Step 3 – Creating the Substrate
Step 4 – Printing the Inner Layers
Step 5 – Ultraviolet Light
Step 6 – Removing Unwanted Copper
Step 7 – Inspection
Step 8 – Laminating the Layers
Step 9 – Pressing the Layers
Step 10 – Drilling
Step 11 – Plating
Step 12 – Outer Layer Imaging
Step 13 – Plating
Step 14 – Etching
Step 15 – Solder Mask Application
Step 16 – Silkscreening
Step 17 – Surface Finish
Step 18 – Testing
Conclusion
After completing our analysis of the Casio fx-300 ES Plus, we have concluded that we were correct in our hypothesis that the purpose of this calculator was to output accurate answers in an efficient manner. We came to this conclusion after successfully completing the reverse engineering process, and answering the question of how the calculator functions. Examining each part, discovering how components interact with each other, and understanding the flow of electricity within the calculator were essential to our arrival at our conclusion. During our analysis, the greatest challenge we encountered was identifying miniscule pieces of the printed circuit board, and understanding their function and how they affected the operation of the calculator. After overcoming this particular aspect of understanding the function, we were able to form accurate connections between parts and their purposes, and how the calculator operates as a whole. The Casio fx-300 ES Plus proved to be safe, produce reliable answers, be cost efficient, and convenient.
Reflection
During this project, we were able to collaborate with three other group members. We found a new way of doing this through the use of a Gantt chart, which was a fantastic way to organize and split up our work as a group. Using the chart, we were able to complete the project on time, and communicate effectively as a team. This was an advantage to our productivity, and something that we will be using in future projects as well.
If we were to improve on any aspect of this project, I would recommend we develop a more efficient way of sharing photos we want to include in the report. We had some difficulty making sure that all of the images we wanted to include would upload, and for this reason, I will keep this in mind for the next project as something I will try to improve upon.