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A project log for (AT) Mega Enigma, a 2560 Pro Mini Enigma Simulator

A minimalist 139x171x50mm Enigma Machine Simulator with working plugboard using an ATmega 2560 Pro Mini and a custom PCB.

Arduino EnigmaArduino Enigma 06/14/2019 at 06:020 Comments

The holes for the  TVS (Transient Voltage Suppression) diodes on the plugboard are a little too tight.

There are two ways to fix this.

1) find a new component with the correct hole size, replace and reroute the traces to each TVS.

2) increase the drill size in the gerber files.

Let's choose option 2.

Export the Gerbers and find the file ending in _drill.txt

The first lines define the tools to use and their type.

line 6 specifies tool T100, a circle of diameter 0.236221 inches. That's a big drill, probably the plugs. Why do we have T100 and T103? They differ by an insignificant amount. The manufacturer will probably use the same drill for these.

Of interest are drills T101 and T102. T1 is not through plated, so those must be the mounting holes on the corners.

Further down the file, looking at the holes drilled with T102, notice that the Y coordinates at the end do not change, so this must be the header at the top.

T101 must be the TVS diode legs then... Let's change Tool 101 to a bigger number, let's say 0.045"

Here is a rendering of the original plugboard:

Here is the new plugboard. The size of the copper ring around the plug has been reduced from 2mm to 1.5 in fritzing. But look at the size of the holes on the TVS diodes.

This is an early experiment. Next, let's measure the actual diode legs and select the final drill size.

This is the second time ever we have had to go into the Gerber files to manually change something. The first one was to correct some lines that were appearing on the production silkscreen on Sinclair boards. The fix was to increase the diameter of the tool used to paint the silkscreen layer. 

The lines at the top of the C letter, log and X were rendered in the production PCB.

The fix was to go in the silkscreen file and slightly increase the tool size so adjacent passes overlap and the line is gone...

Post under #GerberHacks

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