Memory

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Board

Schematic 

Purpose:

The purpose of this exam was to test all of the skills we learned this year. The main focus of the year was creating standalone projects. These standalone projects required us to know how to breadboard, read a circuit diagram, read data sheets, make board layouts in Eagle, read circuits developed in Eagle, etch boards, drill boards, and solder. We also had to know basic functions of common parts, like transistors and SPST switches. This project tests all of these skills by requiring us to read an Eagle circuit diagram, breadboard, and solder.

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Reference:

Final Exam: Memory

Memory:

The goal of this exam is to construct a permanent working version of Memory. Memory is a recreational activity based on an electronic circuit in which the user is required to remember and recall a random sequence of four red and green flashes in quick succession from a bicolor LED.  The user has up to 10s at the end of the sequence to reproduce it by setting each of four switches, from left to right, before submitting his response for confirmation by pressing the TEST switch. If the user’s response is correct, the bicolor LED displays green, otherwise it displays red. A potentiometer (SKILL) can be used to adjust the difficulty of the game by influencing the interval of time between flashes.  A RESET switch is used to reboot the microcontroller.

Task:

1.     You are to breadboard a standalone prototype of the Memory game from the schematic that appears on the next page using the supplied components.  The software has been uploaded to the microcontroller. Raise your hand when you have completed this stage before bringing your circuit to my desk for a demonstration. Take a photo and video of your working prototype for later inclusion in your ER.

2.     Dismantle the prototype and assemble a permanent circuit on the printed circuit board provided for you. Again, raise your hand when you have completed this stage before bringing your circuit to my desk for a demonstration.  

Procedure:

We were given the three-page exam booklet and allowed ten minutes to read it over. After reviewing the task and having an understanding of the circuit we were given a bag containing all the parts needed as well as an ATMEGA328P-PU chip with working code pre-programed on it. We were then set to breadboard a prototype. Breadboarding the circuit from the Eagle Diagram added a few more challenges as opposed to reading a traditional circuit diagram. Because Eagle’s main purpose is to provide a board view to arrange parts, its circuit view has a number of shortcuts that are meant to allow the user to complete the wiring quickly. Eagle designs the parts to be easy to connect, meaning that often the pin layout will be modified so that all wires come out of one side of the part. This means when breadboarding from the Eagle schematic we had to pay extra attention to the pin numbers in case Eagle had rearranged them to allow for easier wiring. The second challenge Eagle presented was its shorthand wiring. To save time wiring a circuit in schematic view, Eagle allows the user to add Vdd and Vss like they are parts. This means that parts that are supposed to have a common ground, for example, never connect in the circuit diagram because they all have separate Vss “parts” connected to them. After we either successfully wired the breadboard or decided to move on due to the time restraint, we were given a pre-etched and drilled PCB and had to solder all the components on to make a standalone version of the game. Soldering was fairly trivial because the holes were already drilled so we just had to put the parts where they fit. However because of the Vdd and Vss problem stated above, adding the voltage regulator to the board required a fair amount of thinking. Because the voltage regulator had to be properly oriented and the capacitors were polarized we had to know which ones went where and how they should be oriented. When I was confident my board would work, I plugged in a 9v power source into the DC jack and was pleased to see that my board worked properly. When I finished, Mr. D’Arcy replaced my ATMEGA328P-PU chip with one that had a higher difficulty level. Because my difficulty level didn’t change as dramatically as it should have both of us realized that I had a 10k resistor where a 1k resistor should be and vice versa. After removing and soldering the resistors in their correct positions my circuit worked perfectly.

Parts List:

Part	Value	Device	Package	Description	Important
328P		DIL28-3	DIL28-3	Dual In Line	Datasheet Pins
C1	10uF	CPOL-USTAP5-70	TAP5-70	POLARIZED CAPACITOR, American
C2	1uF	CPOL-USTAP5-70	TAP5-70	POLARIZED CAPACITOR, American
DCJACK	DCJ0202	DCJ0202	DCJ0202	DC POWER JACK
L7805		78XXL	78XXL	VOLTAGE REGULATOR	Datasheet
LD1		DUOLED-RG-C	DUOLED-C-5MM	DUO LED
LD2		DUOLED-RG-C	DUOLED-C-5MM	DUO LED
LD3		DUOLED-RG-C	DUOLED-C-5MM	DUO LED
LD4		DUOLED-RG-C	DUOLED-C-5MM	DUO LED
LD5		DUOLED-RG-C	DUOLED-C-5MM	DUO LED
R1	220	R-US_0207/10	0207/10	RESISTOR, American symbol
R2	220	R-US_0207/10	0207/10	RESISTOR, American symbol
R3	220	R-US_0207/10	0207/10	RESISTOR, American symbol
R4	220	R-US_0207/10	0207/10	RESISTOR, American symbol
R5	1k	R-US_0207/10	0207/10	RESISTOR, American symbol
R6	10k	R-US_0207/10	0207/10	RESISTOR, American symbol
R7	220	R-US_0207/10	0207/10	RESISTOR, American symbol
S1	TL32PO	TL32PO	TL32PO	TINY SWITCH ON – MOM
S2	TL32PO	TL32PO	TL32PO	TINY SWITCH ON – MOM
S3	TL32PO	TL32PO	TL32PO	TINY SWITCH ON – MOM
S4	TL32PO	TL32PO	TL32PO	TINY SWITCH ON – MOM
S5		10-XX	B3F-10XX	OMRON SWITCH
S6	RACON12	RACON12	RACON12	ITT SWITCH
VR5	10K	TRIM_US-B64Y	B64Y	POTENTIOMETER
XTAL1	16MHZ	10G7A-12.5KHZ	HC49U	Resonator	Datasheet Purpose

Conclusion:

I thought this exam did an excellent job of testing us on the important skills we learned during the year. Soldering under a time limit really pushes you to keep your hand still, solder fast but make sure you are soldering the right things. Reading off of an Eagle schematic requires you to consciously think about the flow of the circuit, understanding how the pins are numbered on the chip and how parts should be wired. This exam also tested our time management skills because there was no set time on how long you should spend on your breadboard or circuit board. Time management was the hardest part of the exam. Everything the exam asked of us we had done before but it had taken days or weeks to complete it. Doing it in two hours really showed how well we understood what had to be done and what we took from our year of work. If I could do this exam over again I would clean up the wiring and placement of parts on my breadboard. At the time I knew we were getting graded on the appearance of our breadboard but because I knew there was a time limit I just put parts on without thinking of the best place they should go. I would also pay more attention when soldering parts onto my circuit board. I had them in the correct place on my breadboard but because of the time limit I was rushing and carelessly mixed them up in the transfer between my breadboard and circuit board.  In conclusion I thought this exam tested us on everything we needed to be tested on and even taught us a new skill, time management. Testing us on writing code would be been a little inappropriate because although hardware needs coding, we did not learn to code this year. As I am very excited to finish high school and embark on new university hardware projects next year I will miss these types of projects as well as the setting, style and person teaching them.