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

Photo Gallery:

               

            Not complete            

                                            

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.

Arduino Audio Spectrum Part 1

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Purpose:

The purpose of this project was to allow each of us to explore a project of our interest. I had wanted to make a spectrum analyzer for a while and this was the perfect opportunity to finally do it. The visual aspect of the project always interested me but recently I had the desire to understand how the project works. This project was also chosen to prepare me for university. I wanted to experience an assignment where little information existed and where it did there was no explanation on how or why it worked. 

Parts List:
*Note* These are only materials used for part 1 of the project

Quantity	Part	Description
1	Arduino (UNO)	http://tinyurl.com/bmr9ofd
1	Audio Cable 3.5mm	http://tinyurl.com/cc6l7vu
1	Audio Jack 3.5mm	http://tinyurl.com/co6mps2
1	Audio Jack Breakout	http://tinyurl.com/bwj4yd7
2	LM3914N	http://tinyurl.com/ccsznaa
1	MSGEQ7	http://tinyurl.com/btxznhl
1	4017 Decade Counter	http://tinyurl.com/c7czttc
2	3904 Transistor	http://tinyurl.com/79a3cuj
5	LED	http://tinyurl.com/c7lmqjc
4	LED Bargraphs	http://tinyurl.com/couynuv
2	0.1uF Capacitor	http://tinyurl.com/cypzca9
1	33pF Capacitor	http://tinyurl.com/bueuzpn
1	0.01uF Capacitor	http://tinyurl.com/d6jhhrk
1	220kΩ Resistor	http://tinyurl.com/brezm5m
8	2.2kΩ Resistor	http://tinyurl.com/brezm5m
1	20kΩ Resistor	http://tinyurl.com/brezm5m
3	10kΩResistor	http://tinyurl.com/brezm5m
1	47kΩResistor	http://tinyurl.com/brezm5m
40	1.3kΩResistor	http://tinyurl.com/brezm5m

Photo Gallery:

Version 1                     Version 2                   Version 3                    Version 4
            


Procedure:
I started by researching other spectrum analyzer projects to see what parts they used and how their code looked. I found two sites that were usefull and decided that it was time to start building. Because I was determined to use LED bargraphs and my desired height was 20 LEDs tall, I had to find a way to drive all of the LEDs. This is where the LM3914N's come into play.
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LM3914N

The LM3914 is a dot/bar display driver. this chip is a monolithic integrated circuit(set of circuits in one chip) that senses analog voltage levels and drives 10 LEDs based on the voltage level, providing a linear analog display. This chip also allows you to choose from a moving dot display or a bargraph display by simply connecting a single pin. These chips control the LEDs by grounding them so you can line them up beside your LED bargraphs and only need to supply your bargraphs with power. Because I am using two bargraphs I need two LM3914s. However instead of using two separate LM3914s you can wire them together creating a seamless display. The LM3914 also allows you to choose the voltage range you want to display by simply choosing resistors. This is because pins 7 and 8 on the LM914 act as a voltage regulator. You can set the voltage range based on this equation:

In my case because I am using two 10 segment LED bargraphs and want to have an overall voltage range between 0-5v I arrange the resistors so that each LM3914 has a voltage range of 0-2.5v and 2.6-5v. 

The LM3914 also allows you to set the brightness of the LEDs you are powering. You can determine the milliamps being supplied to your LEDs based on this equation:

In short, R1 determines the milliamps being supplied to the your LEDs and the ratio of R2:R1 determines the voltage range. If you are cascading the LM3914 chips like I am, all you need to do is give them the same resistor values, connect them together and they will automatically know that you want an overall voltage range between 0-5v (in my case). 

This is an example of how to cascade two LM3914s to drive 20 LEDs:

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After deciding how to drive the LEDs I had to figure out how to read and separate the frequencies. The websites I looked at both used the MSGEQ7 to achieve this task so I researched the chip and decided that it was the one for me. 

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MSGEQ7

The MSGEQ7 is a seven band graphic equalizer that divides the audio spectrum into seven frequencies, 63Hz, 160Hz, 400Hz, 1kHz, 2.5kHz, 6.25KHz and 16kHz. The frequencies are peak detected (only cares if the pin is high) and multiplexed to the output to provide a DC representation of the amplitude of each band. The chip requires an external strobe in order to work. This strobe can be delivered through hardware (a chip) or through software (I used this method). The strobe is what advances the multiplexor. When the strobe pin is high the multiplexor advances by one channel (one of the seven frequencies) and when the strobe is low the reading from that channel is passed through the output pin of the chip. The strobe pin will only work if the reset pin is low. If the reset pin is high, the multiplexor will return to the first channel and will wait until the reset pin is low and the strobe to start. 

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We can now drive a single column of our spectrum analyzer. Now the task is to find a way to drive the other six columns. There are multiple methods of doing this and the immediate thought is multiplexing. Multiplexing is a valid option but there is a simpler way. I used a 4017 CMOS counter or commonly called a decade counter. 

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4017 CMOS Counter

This chip has output pins from 0-9. The counter acts somewhat like the multiplexor inside the MSGEQ7. The chip has a clock pin which when it is high the output pin of the chip increases by one. The output pin will supply power to whatever is connected to it. A single output pin of the chip will be connected to all of the V+ pins of one column of our LED bargraphs. This chip is perfect because if we connect its clock pin to the same strobe as the MSGEQ7 when the MSGEQ7 outputs the measured frequency the 4017 will display that frequency on the appropriate column of bargraphs. Now because the 4017 is a decade counter and we only have 7 columns we connect the pin Out(7) of the 4017 to its reset. We do this because the 4017 will count from 0-6(giving us 7 outputs) and because the seventh pin is connected to the reset pin, when its high the counter will reset. One thing to note is that because the counter is running on a 1/7 duty cycle the LEDs will seem dimmer than usual because they are turning on and off so fast. 

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Putting it all together

This is an infinite cycle that happens extremely fast so it appears that all of the LED columns are on at the same time.