Category: Tanisha’s Status Reports

This week I worked on completing the layout of our PCB and ordering all of our parts. We ordered the rotary encoders, MAX7219 7-Segment Display, SD Card readers, and sourced the remaining miscellaneous parts (Micro SD cards, adapters, buttons, LEDs) . Due to a shortage in stock we could only order 2 rotary encoder instead of 3 so we updated our design to only include 1 rotary encoder.

Nancy and I reorganized our PCB layout to be much cleaner, more historically accurate and updated power considerations. We updated the layout of our PCB to be historically accurate to the actual Enigma machine’s lampboard (different from the standard qwerty keyboard – attached). We also adjusted spacing for 10 mil traces as a safety precaution, updated our button footprint with the new tactile button we settled on and changed the layout to float above the FPGA at a diagonal so the onboard buttons and 7-segment display can be accessed as a fallback option. The in progress PCB layout is attached below.

I worked with Amelia a little on the logic of our PS/2 protocol that she wrote and also worked on finding the solution to a setback when our current PS/2 keyboard didn’t work with the power supplied from the FPGA. Nancy and I are planning to mitigate this potential setback with the SD Card reader by testing the required power level for a measurement to be read. Accordingly, we can build in a voltage regulator to our PCB so we don’t have power issues during integration.

This week I will order remaining small parts including 100 Ohm resistors and  right angled header pins. I also plan to finalize PCB layout with updated power considerations, finish the traces and add silk screen labelling for user friendliness. Once PCB work is done, I will work on formatting and writing our MicroSD cards so they adhere to a format that is readable by our SD Card reader and hence our SPI protocol can accurately extract information.

This week I worked on updating the PCB schematic design as we pivoted (for the final time) from using the Altera DE0 Nano standard FPGA to the Altera DE10 FPGA.

Originally I had worked on expanding our PCB design to be two separate PCBs for the DE0 Nano as the ADC pins for our potentiometer were on the underside of the FPGA and hence we split up the rotor control elements to be on separate PCBs (top layer: microSD card reader, lampboard, keyboard), (bottom layer: potentiometer, MAX7219 display, buttons).

However, when it came to researching the external keyboard, I was looking into different types of ribbon cables and found that the easiest to implement would be with a 30 pin ribbon cable connector to an FFC on the FPGA. The problem with this is we wouldn’t have enough pins on the current set of GPIO pins we were using on the FPGA which meant we’d have to incorporate a 3rd PCB to be used on the other side of the FPGA which seemed like a waste of resources (time, money, space) as it’s just wiring for the keyboard.

Nancy and I worked together to look into alternatives to this solution, and Nancy proposed we use a PS2 Keyboard which simply has a single plug to interface with the keyboard. The alternatives were either creating another plug connector on the PCB that interfaces with FPGA GPIO pins, or during research Nancy found that the Altera DE10 Standard FPGA (that we started with) that actually had an onboard PS/2 plug.

This led to the overhaul of our design as we switched back to the DE10. This led to only a single PCB instead of 2 separate ones and hence I redid the PCB schematic to be as such as attached below.

We also did some hands on testing with the FPGAs to ensure we had the right pitch/pin sizes for our headers and were pleased that we can just use standard headers (as this information was not provided in the user manual somehow).

I also began laying out this PCB design – attached is a screenshot of the in progress layout with descriptive tags.

I also worked on the Design Report and created our new Bill of Materials which is clearly updated with all of our finalized parts according to the new PCB design.

This week I plan to complete the layout of our PCB, send it for ordering, and order all our individual parts so it has enough lead time to get here alongside the PCB manufactoring process. This is slightly off schedule our original plan, however this was due to the frequent switching of design and parts we were planning on using (potentiometers -> rotary encoders, #headers, pcb keyboard -> external keyboard), and hence was a wiser choice to put off ordering till now.

This week I worked on preparing for the design presentation as it was my turn to present. I felt prepared and confident in my slides and content and thought it went well overall. I also continued to fix things on our draft schematic. Since we changed our FPGA, I picked up our new one this week and have been adjusting the schematic to make sure the PCB size and layout matches the DE0 Nano layout and pins. This was a struggle before we had our hands on the physical FPGA as there seemed to be multiple versions of the DE0 Nano and we couldn’t tell which layout/datasheet we should be adhering to. I aim to have an updated schematic done this week so we can get the layout done as soon as possible and send it for fabrication over spring break and continue stay on schedule. If time permits this week, I also hope to return to my external keyboard research so if that arrives after break I can start to mess around with the actual connections and test the ribbon connector. I anticipate this to take a while as it is hardware I am unfamiliar with and tricky hardware issues may take some time.

This week I continued to work on the schematic for our custom PCB. Due to some design changes I had to switch certain components out and ensure that the ones we maintained were able to work with the rest of our components. This required a lot of overhauling of current work (updating BOM and components list) which occupied the bulk of my work this week. Some of the new components included the external keyboard instead of building one on the PCB so I explored some tradeoffs in that area and looked at previous capstone projects that successfully used both options. The current decision is to work with a keyboard through the ribbon cable as opposed to the USB port which was the original reason why we ruled out the external keyboard option. I also updated our Gantt chart and planning schedule based on our new design so the work was evenly spaced out and accurate to the scope of our project.

Finally, I also worked on our Design Presentation slides and started preparing for the Design presentation in the upcoming week as I’ll be presenting for our group.

This week I plan to source further feedback on my schematic (have previously discussed with a peer and faculty on certain design choices) as well as presenting the Design Presentation. This should keep us on our updated schedule as the removal of the Arduino means I’ll be freed up to work on the external keyboard hardware and test it thoroughly.

This week I worked on creating the components list for our PCB. This included researching all the relevant components, finding footprints, and all but ordering the parts. Components included the Arduino SPI interface with SD cards, SD Card readers, 7 Segment Displays, encoders and decoders (which we’ll be using shift registers for) and all required LEDs, resistors and buttons. We pivoted from using encoders to shift registers and single 7 Segment Displays to the Max7219 which took a bit of adjusting on our planned Arduino pin layout. I looked into lead times and shipping costs to decide where we would be ordering from for each of these, made sure it fit in with our planned schedule, and updated the BOM. I’ve also started a barebones schematic and reached out to a third party for peer reviews. This fits in with the scheduled plan as I should be on track to send out the schematic this weekend and get feedback and iterate by next weekend.

Components:

BOM: