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Sudoku Teardown

Creative Commons License Michael Stanley & EE HomePage.com
This report is licensed under a Creative Commons Attribution 3.0 Unported License.

Introduction

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Figure 1: Electronic Sudoku
Sudoku is a game of logic played on a 3X3 grid, each of which contains a smaller 3X3 grid. The object of the game is to insert numbers in the squares of the overall grid such that each row, column, and 3X3 smaller region will contain the digits 1 through 9 exactly once. The game is initialized with a subset of the final solution, and the user has to fill in the rest.

I first came acquainted with the game when my wife had a brief Sudoku addiction a couple of years ago. So I bought several when I caught them on sale at my local Harbor Freight store last Christmas. And of course, I couldn't help but sacrifice one to be the victim of one of my periodic teardowns.

Theory

This is an extremely simple microcontroller-based design. There are only three controls: a reset switch on the back of unit, a power switch on the top of the unit, and the touch panel by which the user plays the game. Feedback is via an LCD display and Piezo-electric speaker. I'll discuss the individual components and design tradeoffs in the teardown below.
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Figure 2: Rear view of the game.

Teardown

As is the case with other EEHP teardown reports, you can see higher resolution versions of most of the photos simply by clicking on the photo.

The design is straightforward. Mechanical components include:

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Figure 3: Reset switch
Electronic components include: Figure 2 shows the back of the unit with the touchscreen stylus extracted part of the way from the unit. The cover to the battery compartment (upper right) is secured via a single screw. The small yellow dot about 1/3 of the way from the left is the reset button, which is shown in further detail in Figure 3.
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Figure 4: Power switch
Not easily seen in Figure 2 is the power switch along the top of the unit (left of that photo). This is shown in Figure 4. Figures 5 and 6 shown the interior of the battery compartment, and a closeup of the single CR2032 Lithium battery which powers the unit.

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Figure 5: The battery compartment
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Figure 6: The power source is a CR2032 Lithium battery

In figure 7, I've removed the battery, and you can now see down to the bracket (mounted directly on the PCB) which holds the battery in place. This is clearer in Figure 8, where I've removed the back of the case. You can now see the black blob of epoxy which encapsulates the single microcontroller which provides the intelligence for the unit. This type of packaging is called "chip-on-board", and we've seen it in earlier EEHP teardowns.

Notice how the PCB is held tightly in place by a number of posts projecting from the front of the unit.

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Figure 7: The PCB is visible below the battery compartment
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Figure 8: The PCB

When we opened the case, the rubber portion of the reset button dropped right out. This is shown in Figure 9. The bottom of the button is conductive. Pressing down on the button forces the bottom portion to come into contact with the PCB, bridging two connectors (Figure 10). Again, this is a commonly used method for constructing controls on all types of electronic equipment.

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Figure 9: The reset button
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Figure 10: Switch contact pattern

In Figure 11, we've flipped the PCB and LCD panels to the right to reveal the touch panel still in place on the front of the package. The PCB and touch panel are connected via a plastic ribbon connector shown in Figure 12. The ribbon connector was mounted to the PCB using Scotch Tape!

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Figure 11: PCB to touch screen connections
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Figure 12: Closeup of the ribbon connector

Backing up a bit, Figure 13 takes the configuration shown in Figure 8, and removes the PCB, but leaves the LCD in place. Notice the elastometric Zebra connectors along two sides of the LCD. The LCD is held in place via pressure using the Zebra connectors, which also provide connections to the LCD. The connector pitch of the Zebra is smaller than the pitch of the PCB pattern, resulting in an assembly process that is self-aligning.

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Figure 13: The back of the LCD
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Figure 14: Closeup of one of the Zebra connectors

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Figure 15: LCD, PCB & Zebras
Figure 15 illustrates the connecting sides of the PCB and LCD, laid side by side, with one Zebra in place on the LCD, another on the PCB.

In Figure 16, we've removed the LCD. You can now see the touch screen. You also get a better look at the black plastic retainer that keeps the LCD in place above the touch screen.

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Figure 16: Note placement the plastic guide for the touch screen

The bracket has been removed in Figure 17, and we are left with only the touch screen in place adjacent to the front of the unit (Figure 18).

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Figure 17: Only the touch screen remains
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Figure 18: The front panel

Figure 19 is a detailed shot of the touch screen, showing some of the conductive patterns on the screen. This technology is known as "Film-on-Glass".

Finally, let's flip over the back of the unit detached earlier. That gives us Figure 20, where you can see the piezoelectric speaker used for sound effects.

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Figure 19: Patterns on the Touch Screen
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Figure 20: Patterns on the Touch Screen

Concluding Remarks

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Figure 21: The fully disassembled unit
This game design is simple and elegant. There are no extra components, and cost has been reduced to a minimum (I think I only paid around $6 for my unit last Christmas).

Finally, Figure 22 animates the disassembly process to give you a better idea of how the various parts fit together.

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Figure 22: EEHP "Automated" Disassembly

To Learn More

You can improve your learning experience by investigating the following resources:

Re-Use

Creative Commons License Michael Stanley & EE HomePage.com, June 2008

The original publication of this report resides at http://www.eehomepage.com/report.php?report=20080620.

This report is licensed under a Creative Commons Attribution 3.0 Unported License.

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