12/2/2025 3 PM - creating the design and making the schematic

I wanted to create an offline device that securely stores my passwords and gives them to me only after I enter a master password. While looking into strong encryption options, I found the ATACC608PSHTA, an authentication and cryptography chip that supports 16 secure keys and provides excellent hardware-level protection. This led me to change my idea from storing passwords to storing authentication keys instead.

Since I want this device to last for months on a single battery, I chose a 0.96" SSD1306 OLED display because it uses very little power. For accurate timekeeping, which is crucial for authentication devices, I selected the TS3231MZ+TRLCT real-time clock module (I²C, 8-pin).

For power, I decided to use a coin cell. For input, I first considered push buttons, but they take up too much space and can be unreliable. So I switched to a rotary encoder + 4 push buttons
, which provides a clean and safe password entry experience.

To streamline power management, I chose the seed studio xiao ESP32-S3 since it has a built-in battery charger. I also added a simple resistor-based battery level sensing circuit. Completing the research and schematic design took me about eight hours of work

12/2/2025 4:04 PM - Footprint Assignment & PCB Layout Initialization

I started by assigning footprints, which was tricky since I’m new to PCB design and had to look up various switch types and footprint standards. After I found and assigned all the footprints, I began the PCB layout, keeping the board compact at about 60 mm × 40 mm. On the front, I placed the 0.96" OLED, the rotary encoder, four push-buttons, and the XIAO ESP32-S3 module. The back holds the coin cell and the other modules. To provide physical protection, I’m thinking about covering the cryptographic chips in epoxy resin. This way, removing them would damage the device. This process took me about three hours.

12/2/2025 4:08 PM - Routed the PCB

In this stage, I routed the entire PCB, a process that took me around four hours. Since Blueprint doesn’t allow auto-routing, I had to route every trace by hand. The result looks a bit messy, and I don’t think it’s the best layout I could create, but it’s also far from the worst. Overall, it’s a useful first routing pass, and I can improve it later if needed.

12/2/2025 5:22 PM - Final PCB Styling and Clean-Up

In this step, I gave the PCB its final polish. I added a stylish AEGIS label, which is the name of the design, on the top layer. I also included an Enigma rotor graphic to symbolize encryption. At the bottom, I added a fun tagline: “No radio. No cloud. No leaks. Air-gapped hardware enclave.” After that, I cleaned up all unnecessary markings and made the board look neat and visually consistent.

12/2/2025 5:34 PM - Keychain Mount Integration

For a final adjustment, I decided to add a keychain holder to the PCB. Since the device is small and designed to be portable, adding a keychain attachment seemed practical.

12/2/2025 9:03 PM - BOM and cart

AMAZON.IN ORDER

Component: Seeed Studio XIAO ESP32-S3
USD: 21.13

Component: Solder Paste (Mechanic/PagKis)
https://amzn.in/d/03WiCx5f
USD: 5.44

Component: 0.96" OLED Display (I2C)
https://amzn.in/d/0bmdNpzb
USD: 3.32

Component: Energizer 172(Pack of 1)
https://amzn.in/d/0ebEjmQO
USD: 1.32

Delivery Charge:
USD: 1.11

AMAZON TOTAL:
INR: 3028
USD: 33.52

ROBU.IN ORDER

Component: LiPo Battery 2500mAh (JST-PH 2.0mm)
https://robu.in/product/wly104050-2500mah-3-7v-single-cell-rechargeable-lipo-battery/
USD: 6.64

Component: 10nF Ceramic Capacitor (0805 SMD)
https://robu.in/product/10nf-0805-surface-mount-multilayer-ceramic-capacitor-pack-of-50/
USD: 0.055

Component: Female Header 1x40 (2.54mm)
https://robu.in/product/2-54mm-1x40-pin-female-single-row-header-strip-pack-of-10/
USD: 0.077

Component:Pin Male Single Row Straight Short Header Strip x2
USD: 0.13

Delivery Charge:
USD: 0.54

ROBU TOTAL:
INR: 643.2
USD: 7.15

DIGIKEY ORDER
here is the file containing the order
2025-12-02T065013

Idx 1
Qty: 1
Part: DS3231MZ+TR
Description: RTC Clock/Calendar (I2C, 8-SOIC)
USD: 10.64

Idx 2
Qty: 1
Part: ATECC608B-SSHDA-T
Description: Auth Chip (8-SOIC)
USD: 9.00

Idx 3
Qty: 1
Part: EC11E15244B2
Description: Rotary Encoder
USD: 4.85

Idx 4
Qty: 1
Part: OS102011MS2QN1
Description: Slide Switch SPDT
USD: 0.71

Idx 5
Qty: 1
Part: S2B-PH-K-S
Description: R/A 2-Pin JST-PH Header
USD: 0.10

Idx 6
Qty: 1
Part: 1060
Description: CR2032 Battery Holder (SMD)
USD: 1.13

Idx 7
Qty: 10
Part: RC0805FR-07100KL
Description: 100K Resistor
USD: 0.30

Idx 8
Qty: 10
Part: RC0805FR-0710KL
Description: 10K Resistor
USD: 0.14

Idx 9
Qty: 10
Part: CRCW08054K70FKEA
Description: 4.7K Resistor
USD: 0.41

Idx 10
Qty: 10
Part: CRCW08052K20FKEA
Description: 2.2K Resistor
USD: 0.41

Idx 11
Qty: 10
Part: CRCW08051K00FKEA
Description: 1K Resistor
USD: 0.41

Idx 12
Qty: 10
Part: C0805C104K5RACTU
Description: 0.1uF Capacitor
USD: 0.16

Idx 13
Qty: 5
Part: B3FS-1002P
Description: Tactile Switch
USD: 2.25

Idx 14
Qty: 10
Part: RC0805FR-07220RL
Description: 220 Ohm Resistor
USD: 0.09

Components Subtotal: 30.60
Tariff (Estimated): 1.77
FedEx ground: 6.99

DIGIKEY TOTAL: 39.36 USD

PROJECT GRAND TOTAL = 80.03 USD

12/2/2025 9:43 PM - some rendering and testing

n this step, I tried to render the design, but I had a hard time exporting the STEP files, so I left them out. Then I exported the design and checked that all the modules fit together. I also exported the file to a 3D viewer, and here’s an image of that.

12/2/2025 10 PM - PCB Production Order and Cost Breakdown

In this step, I quoted the JLCPCB order. I tried to get all the settings right, but I’m still new to this, so I did my best. The PCB cost is $2, and the shipping estimate is $13.42, totaling $15.42.

Now, if I add this to the $80.03 I spent on parts, the total for the project is $95.45. This includes the $5.44 worth of solder paste that I’m adding to the cart. With that excluded, the final cost is $90.01
So this project is a 3rd-tier project

12/2/2025 11 PM - Firmware

In this part, I decided to design the PCB. I’m writing the code in an .ino file because it’s easier for me to understand and work with Arduino code. I created the necessary logic since all the devices on this PCB share the same I²C lines, which was the challenging part.

12/24/2025 - here is the ATECC608B

Here you can see the 2 chips in the schematic mode

Here you can see 2 of ATECC608B in 3d viewer mode

Here you can see the ATECC608B alongside with DS3231MZ

The chip is actually placed on the backside of the PCB, so it's not visible in the photos I uploaded in here