Sunday, January 26, 2020

Mega Enigma Assembly Steps

1) Power Jack
2) Keys
3) Arduino Mega
4) 16 Segment Displays
5) Lamp Field
6) Plugboard sockets
7) Shorting PCB
8) TVS Diodes
9) Copper bus on common side of TVS Diodes
10) Header
11) Bend Header
12) Solder Plugboard Header to Main Board

Saturday, January 18, 2020

Mega Enigma Software V12 Released

This version focuses on operational realism of the enigma machine.

Sometimes, modules get a little hacky from adding features one at a time. Once all the features are defined, it is better to rewrite a function from the ground up and it comes out cleaner.

ProcessEnigma() in EnigmaGUI.ino has been rewritten, particularly case 2 in the finite state machine.

The machine has been designed to operate as follows:

Pressing a key first moves the rotors then lights up the correct result. While the rotors are moving, the contacts are not making, so nothing is illuminated.

A key must be held pressed down to illuminate a result, releasing the key turns off the lamp.

Two keys can be pressed at the same time. The way the keyboard circuit is arranged, the two top rows are in the same zone, while the bottom row is on a separate zone. The rotor up and down keys are in a separate zone. The menu key is in the same zone as the bottom row. Pushing two keys in the same zone corrupts what is displayed. Pushing keys in separate zones does not corrupt the display. Normally, only one key is pushed at a time in an enigma machine, so this zone arrangement is not part of the normal operating procedure.

If the menu key is pressed while a key is being held down and its result is illuminated in the lamp field, exiting the menu restores the current position of the rotors and the illuminated result.

While holding a key down, the rotors can be changed. The lever mechanism of the enigma machine allows each rotor to be advanced while a key is held down, but the ratchet mechanism does not allow an engaged rotor to be moved backwards while a key is pressed.

The fast rotor always turns, so if a key is pressed, it cannot be moved back to the initial position, only advanced. The middle rotors can be moved back until the stepping notch is engaged.

Changing a rotor with a key pressed down changes the output shown in the lampfield.

The plugboard is scanned dynamically. Changing a plug with a key pressed down changes the result shown in the lampfield.

The original Enigma Machine uses a two way switch in each key. If a key is not pressed, it is connected to its corresponding lamp in the lamp field. Pressing a key down connects the battery to the key and sends it to the entry rotor (ETW). The current goes through the rotor maze in and out of the reflector (UKW), and back through the rotor maze into the ETW and through an unpressed key it connects to the lamp field.

Lets use the default settings for an M4 machine with a B UKW and a Beta thin wheel and the rotors at AAAA. Pressing the V key results in E lighting up. V and E are in different zones, so both keys can be pushed down simultaneously without display corruption.

If, while holding V down, the E key is pressed, the path to the lamps would be disconnected in both ends in a real enigma machine, nothing lights up. In this simulator, this behaviour is modeled in software.

Releasing only the V key lights up the V lamp, releasing only the E key lights up the E lamp. Changing the rotors with both V and E pressed illuminates two different lamps in the lampfield. Installing or changing a plug from V or E to any other plug will illuminate two lamps in the lampfield.

So, generally, pressing a key and the key corresponding to its result simultaneously results in both lamps turning off as there is no path to the lamps.

The sequence to illuminate a key in an external USB lamp field is sent out the serial port when a key is pressed.

If the Mega Enigma Machine Simulator is connected to a computer, the Arduino IDE Serial Port Monitor can be opened used to interact with the simulator.

Sending !aaaa sets the rotors to position AAAA. Sending text encodes it. Changes to the machine configuration cannot be made through the serial port, only the rotor position can be changed.

Other unchanged features are:

Holding down the menu key results in an emergency zeroisation. All the settings are cleared and returned to a default M4 machine with B UKW and Beta additional wheel. The ring is reset to AAAA and the rotor position is changed to XXXX to indicate the settings have been cleared. Any physically installed plugs would need to be removed to complete the key erasing procedure. If software plugs were in use, they are cleared. The built in UKWD is reset to 0 as well.

The menu key is ignored for a fraction of a second when the simulator exits out of the menu and returns to the operational mode. This makes it easier to not reenter the menu and stay in operational mode if the menu key is pressed rapidly to advance through the menus and exit.

A hex uploader can be downloaded below:

Full Source Code:

Monday, January 13, 2020

Measuring Battery Run Time By Writing Checkpoints to EEPROM

One way to measure how long a device runs on batteries is to use another Arduino with a Light Sensitive Resistor. Can we do better than that and have the device self monitor without using any external attachments?

How to measure how long will a device run on batteries by writing time stamps to EEPROM.

The key to this algorithm is to either use an external stimuli to set a ram variable or use a different sketch to write a special variable to EEPROM to enter a special routine that writes the value of millis() to EEPROM. Once this special routine is entered, the EEPROM flag that was used to enter is cleared. This way when the device under test runs out of batteries and starts rebooting, the recording routine is not entered again. In EEPROM we will have a series of ever increasing 32 bit values. The only thing remaining is to read all the values and find the maximum. In case the device reboots while writing to EEPROM, an additional check is that the maximum value must equal to the second greatest value plus whatever the time increment used. 

In order to implement a wear leveling algotithm, the time values are written to an EEPROM zone in a circular buffer fashion.

Check out the actual code used to implement this functionality:

The timing routine was run with a used battery and the recorded values were displayed. EEPROM address 701 contains the value of millis() when the recording function was first entered, subsequent values are recorded every minute.

This 9V battery was used, so after 58 minutes, the machine rebooted and stopped recording values. The remainder of the buffer contains 0 left over from the initialization procedure.

Trying again with a fresh set of batteries. After the batteries are allowed to run down, connecting to the device shows a message stating that the endurance test has been run.

This time the test ran for a longer time. The circular buffer was configured from addresses 701 to 3501, storing a 4 byte values lets us write 700 values before reaching the end of the buffer. If a value is stored every minute, the buffer will store 11 and a half hours of data. 

Memory location 3133 contains the highest value recorded, 78540001 milliseconds or 21.8 hours. The value in 3137 is lower, indicating that the code was in its second pass over the circular buffer. By using the wear leveling algorithm, each memory location was used once or twice.

The configuration values of the timing routine were changed to use a larger buffer after the test was run. Memory locations starting at 3501 were left uninitialized at 255 and show the maximum possible number for an unsigned long.

This throws the report off. One can go back and look by hand for the tell tale incrementing values followed by a lower value.

Here are the values for the larger buffer:

If we change that to match the size of the original bufffer:

Now the report runs right and finds the correct value:

58 minutes for a used 9V battery and 21.8 hours for a fresh set of AAA batteries. A fresh 9V battery should run about 8 hours.

And the standby runtime for the Mega Enigma on a fresh set of AAA batteries is a respectable 21 hours. Pressing keys and illuminating results in the lampfield will reduce that time, but code would have to be written to simulate keypresses and illuminate results.

 Now the question is, how long will the device run on a fresh set of AA batteries. The bigger the batteries, the longer the runtime...

How to put a battery compartment inside a laser cut enclosure.

Designing the battery compartment:

A template with all the pieces for an AAA battery holder.

An AA battery holder.

The laser cut files for an enclosure:

How the battery compartment looks like 

A hex nut piece was used as the first one to allow a small piece of plastic to keep the screws captive in the lid. The actual hex nut is sandwiched further down the stack in between two pieces with small holes.

coupled with a 9V plug, a device can be powered by the built in bateries or an external 9V battery.

A two way power switch selects between the internal and external power sources. Selecting the external source when there is nothing connected or the internal source when the battery box is empty turns off the machine.

Download the design files here:

Friday, October 25, 2019

Get your head out of the Cloud(s) and design complex shapes PCB using Free and Open Source Tools

This post will show how to use the CAD program Sketchup to design an arbitrarily complex PCB shape that will be post processed with Inkscape so that Fritzing will accept it as a board outline and produce Gerber files that can be sent to a PCB Fab for production.

The 2019 Saintcon Cybersecurity Conference Badge is an Enigma Machine.

The badges can be interconnected and form a circle in the shape of an Enigma Machine Rotor Wheel when 26 of them are put together.

We are currently designing a new Universal Enigma Machine Simulator.

Let's design a new PCB shape for this project. Fritzing accepts specially designed SVG files as PCB outlines. We need a way to design the SVG files first.

Sketchup is a 2-D and 3-D capable CAD program that's easy to use and can produce dimensionally accurate designs ready for laser cutting or 3D printing.

Sketchup has recently stopped updating the downloadable version and gone to the cloud. The free cloud version does not support exporting to SVG or downloading from the Extensions Warehouse.

Been using Sketchup to design enclosures for a while

Once an enclosure is designed and the finger joints drawn, the faces are selected, exported to SVG and placed in a Ponoko template for laser cutting in 3mm Birch Plywood.

Recently I have started using Sketchup to design objects for 3D printing as well.

The goal is to make a new PCB Shape for this. The dimensions of the rectangle are 139mm by 171mm.

This post expands upon a previous one showing how to do a custom shape using Inkscape and Fritzing. First, Inkscape is used to generate an SVG file with three layers (board, silkscreen, silkscreen0). Fritzing will use this SVG file as the PCB outline.

Let's get started...


Use the circle tool to draw a 26 segment circle. Press C, type a number, then type S26 to select 26 segments and finally draw the circle. The semicircular shape is drawn by first drawing a circle and then attaching two circle segments to the sides. The portions of the circle that are not needed are erased and we are left with a wavy contour.


The same technique is used to draw a 26 side circle, the width of the segment is set to 140mm by measuring it with the tape tool and then 140 is typed to resize the measurement to the desired value. The height of the PCB shape is set to 171mm. Then the width of the top of the shape is measured and the wavy shape in step 1 is resized by using the tape tool and copied and pasted to this file.

The bottom of the shape is flat but it can be made into a semi-circle by selecting the circle and specifying that it will have 96 segments instead of 26.


Here is the final shape. The width at the bottom is 140 mm and the height of the rectangle is 171mm.


Using an export plugin, the shape is saved as an SVG file.


Open Inkscape and load the SVG file generated in the step before.


Go to File-> Document Properties and click on Resize Page to Drawing or Selection. This step can be omitted.


Using the Fill and Stroke tool, color the inside of the PCB. Any color is fine. Select something easy on the eyes. The PCB is rotated as well. (Rotating the PCB is also optional, it can be done at the end in Fritizng). Add three layers, name them "board", "silkscreen" and "silkscreen0". These names are for display only, the file will need to be edited to locate the XML "id" property and set it to match the display names.


Fritzing does not use the XML label property. It needs the ID property set. For that we need to edit the XML that makes the SVG file and change the layer ID properties.

Go to Edit->XML Editor, or press CTRL+SHIFT+X

Look for a line that says  inkscape:label="board", click on it.

Click on the "id" attribute on the right, click below the 'Set' button and type "board" without quotation marks and then click on the "Set" button.


Repeat for "silkscreen" and "silkscreen0" The layer attributes should now be as shown below.


Open Fritzing, Click on the PCB tab, click on the default PCB and on the Inspector window, click the "load image file" button.


Navigate to where you saved the Inkscape SVG file and select it.


A warning dialog will be shown, click OK and the PCB should be displayed. If it is sideways, click on "rotation" on the Inspector window and set it to -90


An existing design is copied from another file into this. Notice that the shape of the PCB is accurately dimensioned.


Rearrange any parts, save the file and export for production, select "Extended Gerber..."


I prefer the look of tented vias, covering with soldermask the plated holes that connect traces in different layers.

This article shows the difference between tented and exposed vias.

The steps:

-Save Work
-File->Export->For Production->Extended Gerber, create "tented" folder
-Routing->Select All Vias
-Press Delete key
-Export Gerbers to no-vias folder

-Copy maskTop and maskBottom, silkTop and silkBottom files from no-vias to tented folder


The mask and silkscreen files from the no-vias folder are copied to the vias-folder. This will ensure that the vias are covered with soldermask and if text is drawn above them, the silkscreen will show.


The Gerber files are put together in one ZIP file and uploaded to

And it is a fail. Instead of a purple board, we get a white one. The contour is open. Time to find where.


Finish the import process at OSHPark, save the defective board and click on the board image, look for discontinuities in the outline. Here we have found one.


Go to Sketchup and add lines in the problem area, delete any doubled up lines and repeat from step 4. This step might be difficult. Sketchup may decide that the contour is no longer closed even though it appears so. Keep adding lines and deleting doubled up lines until the contour closes again.

When repeating the setup process in Inkscape, this time the shape was not rotated and the document was not resized (steps 5-6). Instead the PCB was rotated -90 degrees in Fritzing.


Repeat the Gerber export process and inport to OSHPark.

Success. It took a couple of tries, but finally we are rewarded with a purple board.


Finish the import process and then click on the board, make sure things look ok.

Here is an example of a 3D printed design being turned into a PCB. We will start with this 2-D Kokopelli figure and follow all the steps in this write-up.

And we get rewarded with a white board, another failure. Click on the board image and look for discontinuities in the outline.

The discontinuity was found in the lower arm elbow.

Going back to Sketchup, a circle with more segments was added to the lower elbow and the import steps repeated. This time we get rewarded with a properly rendered board.

This board will not manufacture 100% as drawn given the limitations of the routing bit used to cut the outline of the board. Sharp inner corners like the one where the lower arm touches the body and the flute will have a rounded edge.

Future work: