So below is a demo of the USB adapter for the 5200 where the Start/Pause/Reset/Keypad buttons are now working. However, I'm still having problems Getting the Joysticks to work properly. This is especially frustrating considering that someone else made a custom 5200 controller using the same DAC chip I'm using, and theirs seems to work just fine.

I've been aware of that project for awhile, but I didn't realize they used the same AD5242 DAC chip that I'm using until tonight while I was searching for solutions on YouTube.

Anyway, here is the video of my USB adapter:

People with a close eye will notice that Pac-Man isn't really going in the direction I am trying to steer him. This is because I tweeked the C++ code in this build, trying to find better DAC values... and obviously I got it wrong. Also, you may have noticed that I was confused as to which button was the "Reset" button. I kept pushing the Pause button at the start of the video when I was meaning to push the Reset button... eventually I figured it out... I guess those buttons need labels after all.

Function Buttons

Anyway, here is how the Start/Pause/Reset/Keypad buttons work.

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The function buttons "Start", "Pause", "Reset" are always usable.

Start - "Back" button (aka the button to the left of the glowing Atari Button)

Pause - Glowing Atari Button

Reset - "Ham" button (aka the button to the right of the glowing Atari Button)

I chose these buttons because they match the left-to-right order of the SPR buttons on the original 5200 controller.

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Keypad Buttons

To engage Keypad functionality, the user must press and release the Right Shoulder Button. When in Keypad mode the joystick and fire buttons do not work. To exit Keypad mode, the user must press and release the Left Shoulder Button.

The row selection of the keypad is done through use of the D-pad.

Centered  (C)  - Row 1

Up           (U)  - Row 2

Left          (L)  - Row 3 [Actually, Right also works]

Down       (D)  - Row 4

Column selection is through the use of the XYB fire buttons.

X - Column 1

Y - Column 2

B - Column 3

As such, the Keypad uses the following layout:

       X    Y   B 

     -------------

C   | 1 | 2 | 3 |

     -------------

U   | 4 | 5 | 6 |

     -------------

L    | 7 | 8 | 9 |

     -------------

D   | * | 0 | # |

     -------------

Anyway, even though that YouTube video about the making of custom 5200 controller is 4 years old, I posted on the group's forum hoping to get some feedback from them about what values they used to set the DAC.

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EDIT

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I should add that the fire buttons work perfectly, though you can't really demo that using Pac-Man. When not in Keypad mode, the A, X, and Left Trigger are the 5200 bottom fire button (as I read that most games usually use the bottom button as the main button), and the B, Y, and Right Trigger are the 5200 top fire button.