Arduino Audio Spectrum Part 2

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Purpose:
This is a part two of my three-part Arduino Audio Spectrum project. The purpose of this part was to design and make a circuit board for the spectrum analyzer. This required a greater understanding of eagle and serious thought in designing the board.

Parts List:
*Note* These are only materials used for this part of the project

Quantity	Part	Description
2	Plastic Paper	http://tinyurl.com/blu8q5a
3	UV pre-sensitized copper clad board (single sided)	http://tinyurl.com/cb6j6px
1	Light etching kit	http://tinyurl.com/ptc3g9
1	ATTiny85 to replace Arduino Uno	http://tinyurl.com/buf8xwf

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Procedure:
There was no hurdle to get over in this part of the project. The only way to complete it was to put in the time and think about it constantly. The most difficult part was deciding how to create a circuit board to house all of the parts. My teacher presented the idea of using multiple boards and layering them on top of each other like using multiple arduino shields. The LEDs had to be on top. Because they LEDs took up so much room on a 3x4 board, the only other thing on the top board were seven male pin headers, each supplying one column of LEDs with power. To minimize the number of traces on one board we decided the second (middle) board will only supply ground from the LM3914's to the LEDs. The third (bottom) board houses all the main components such as the LM3914s, ATTiny85, MSGEQ7, 4017, DC jack, audio jack and transistors. We used the grid feature in Eagle to measure and record the placement of pin headers. Because we were stacking the boards and running power and ground from the bottom board to the top board we had to know that the pin headers would line up. I spent the most time on the layout of the bottom board because it had so many parts on it. After completing the board layout in Eagle we printed out the design on plastic paper, put the paper on top of the UV sensitive copper board and put the pair underneath a UV light for ten minutes. We then took the board and let it soak in the developer for five minutes or until we could see the board design showing on the copper. Then we put the board in acid to dissolve the copper not covered by the board design. After about half an hour the circuit board was successfully etched.