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Design Process: To design this project, we brainstormed ideas about what would make a cool soldering kit. After tossing several ideas around that included speakers, solar power and LEDs, we decided to make a board that cycles 16 LED’s in a circle. We originally planned to have one circle with LED’s at opposite ends cycling counter clockwise and clockwise. This evolved into having two circles with LEDs circling in opposite directions. However, when designing the layout, it became apparent that 16 LEDs were too complicated, so we reduced that design to only 8 LEDs. To cut costs for ordering the boards, we decided to shrink the board from a 4 by 6 to a 2 by 3 and to order big boards and cut them into smaller boards. In order to verify the schematic, we built a breadboard version. At first, the breadboard did not work. We tried changing resistors and capacitors, but nothing happened. Then we were introduced to the idea of using a transistor to control several pins on the shift register. After adding the transistor to the circuit, the board still did not work until we discovered that what we thought was a 100k resistor was a 100M resistor. Next we etched another prototype board by laying down tape and putting the board into a solution of FeCl2. Our first board was etched poorly and many of the traces were cut off. Our second board etched properly, but the layout was incorrect and the holes for the components were too large. The third board worked perfectly on the first try after getting a smaller drill and triple checking the layout. This led the way to ordering the real boards from PCB123. We decided to duplicate the design four times and paste the design on a 4 by 6 and when the boards arrived, we were going to cut them. We also had to mass order components to make the kits. When our orders arrived, we noticed that the boards had the capacitor print different. Instead of C1, C2 and C3, there was C4-12. Apparently PCB123 had changed the numbering, but the other components were fine. We decided to make several versions of the instruction booklet. We soldered a board, but it didn’t work. We checked the layout and schematic, and oscilloscoped the board, but didn’t find anything except we forgot to ground the shift register. Later we found the transistors we ordered were slightly different than the transistors we were using before and the transistor had to be put in backward. We built another breadboard and oscilloscoped it and compared it to the non working board. There were no major problems and we were beginning to get frustrated. When the breadboard was meticulously compared to the non working board, we found that DS2 was the problem. We changed a resistor and the board worked. |
For questions and comments contact prhsinventeam@gmail.com.
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