LED Dice 2 - Dice Printed Circuit Board
Abstract
The objective of this project was to design and assemble a printed circuit board (PCB) for a kit sold by Carl’s Electronics called LED dice with slowdown (CK900). A button on the board is pressed, leading a 14017 IC to randomize the number eventually displayed on the LEDs, and a 555 IC timer to slow down the speed of the number displayed. An array of 7 LEDs was used to display the number in the same format as that of a die. The circuit was based of a schematic provided in the kit, which was then replicated in DipTrace to produce a new PCB. The final PCB was manufactured then shipped to Cal Poly for final soldering and assembly.
Project Description
This project utilized various components in a kit from Carl’s Electronics to form a circuit representing a die (Table I). Some components were not used from the original kit including mounting screws, a PCB mounted switch, and a case for the original PCB.
All of the components were measured and modeled in DipTrace to create a component library. The component library was used to create a schematic based of the circuit diagram given with the kit (Appendix 1).
The schematic was used to create a board layout (Figure 1), which was rigorously tested to insure that all the traces connected the correct components. An error in the component library would cause later problems (both of the ICs were modeled with the pins in the wrong order).
Figure 1: DipTrace was used to create a layout of the board. The green areas are screen printed white in the final board, while the black (top side) and gray (back side) represent the conductive traces, vias, and pads of the board.
After the PCB layout was complete, files for the traces, screen-printing, pads, vias, and mounting holes was sent to a manufacturer to be created. The board as received is shown in Figure 2.
Figure 2: Final board produced from layout, note the fiducial marker in the lower right part of the board (silver plus sign).
The board was assembled with all of the components (Figure 3) with the ICs on the back of the board to solve the problem of reversing the IC leads. The lead spacing for the transistors could be reduced to allow the transistors to sit closer to the board, increasing the reliability of the board (less probability of leads being bent during use).
Figure 3: Final assembled board; the ICs are attached on the back of the board. The LEDs currently show the number 3.
Conclusion
This project did an excellent job of demonstrating basic PCB manufacturing techniques. The relative complexity of the project required more thought when designing the PCB, leading to a more dense board when compared to other simpler projects. Although this project required attention to detail and a significant amount of effort, the reward in the form of future confidence to create a PCB from scratch was well worth the energy.
In the future, I would recommend purchasing two kits instead of one. The original kit purchased was short one BC557 transistor, delaying the project. In addition, the original assembly of the circuit (inserting the ICs backwards) caused IC damage, which would have been less of a problem had backup parts been immediately available. With my project specifically, more attention should have been paid to the pin layout of the ICs, however I was lucky that simply inserting the ICs from the back of the board solved the problem. Although not a huge issue, increasing the resistor lead spacing would allow for greater ease during the assembly of the final board.
Downloads
- Presentation (PDF)
- BOM (PDF)
- Schematic (PDF)
- Layout (PDF)