EV Display: Enclosure and LED Design

The EV Display aims to resemble a D-cell battery. Early prototypes focused on design constraints driven by the availability of off-the-shelf components, including 8x8 and 16x16 flexible arrays of WS2812 individually addressable RGB LEDs.

Prototyping the Enclosure

First Prototype: 16x16 Pixel Matrix

Initial tests used a 16x16 pixel matrix to explore enclosure design and parameters like:

• Distance between the opaque shell and LEDs
• Light output
• Resolution of the display

To improve the surface finish, I experimented with post-processing 3D-printed materials using automotive filler and paint.

Putting it all together and playing a simple color fade looks like this:

This design proves to be too bulky. The spacing of the LED’s is perfect, but the light output is too high, resulting in poor dimming and color gradients. It also gave me a lot of interesting challenges and I have designed many solutions to be able to use these flexible LED matrixes in this design. Considering print times and single-filament printer limitations, I have created many revisions of a multipart enclosure to be able to achieve tight fit around around the opaque shell and to retain the led matrix.

The design above has a lot of flaws still. It relies on rings to hold the led matrix together and aligning the top and bottom cap. This also results in a lack of weight of the design. I was working on another revision that uses a simple metal tube as center shaft around which the led matrix could be mounted, but since many other design requirements were not satisfied by this design I moved to another scale for the next iteration.

1. Too Big: This design is too big to be attractive. It would also result in higher shipment and warehosing costs.
2. WS2812B Limitations: High light output of the 5050 RGB LEDs resulted in reduced color control and resolution due to the need to cap brightness at 10%, leaving only 25 effective brightness levels per primary color.

Second and Third Iterations: 8x8 Pixel Matrix

Subsequent prototypes were based on 8x8 pixel matrices. The entire design is based on a proportionally scaled D-cell battery, with enough space to fit the Pixel Matrix. Of course this design introduced new challenges:

1. Flexible Pixel Matrix Stress: Excessive stress on the flexible arrays reduced reliability.
2. Resolution: With this matrix only 8 levels of battery charge can be indicated

This led to a shift toward LED strips with different addressable pixels and alternative designs. In a later version other LEDs are preferred, but while prototyping I want to work with readily available, cheap components as much as possible. To address the dimming challenges I have tested many common Addressable LED strips. The other important test matter is the distance to the opaque material. I remained with this form factor since I already had several sections of the semi transparent tube. The base design was altered to support sliding in different led strips, at various distances from the shell; 6-strip core, 7-strip core, 8-strip core.

Current Design Direction

Flexible PCB for LEDs

The next step involves designing a custom flexible PCB:

• Uses 5050 style packages initially but will transition to smaller LEDs.
• Reduces light output while maintaining or increasing resolution.
• Addresses the lack of high-density LED strips with smaller packages in off-the-shelf options.

Addressable LED Pixels: The SK9822 Advantage

After testing multiple LEDs, the SK9822 emerged as the best option due to:

• Two-Wire Communication: Unlike the WS2812B, SK9822 uses separate data and clock lines for faster and more stable performance.
• Global Brightness Control: Offers an additional brightness control byte, allowing nuanced brightness adjustment without altering color hue.
• High PWM Frequency: Results in smoother color transitions and minimizes flicker during filming or peripheral viewing.

Testing and Comparison

To evaluate different pixel strips, a simple testbench was built for rapid testing and comparison.

Electronics: Leveraging the ESP32 Microcontroller

The ESP32 is used as the primary microcontroller due to its advanced features, making it ideal for IoT and production-ready applications.

Secure OTA Updates

• Fail-Safe Mechanisms: Dual OTA partitions allow seamless updates, with a fallback to the previous firmware in case of failures.
• Encrypted Updates: TLS encryption ensures only authorized firmware is deployed.

Data Security and Firmware Protection

1. Flash Encryption: Secures firmware and sensitive data against unauthorized access.
2. Secure Boot: Ensures only trusted, signed firmware is executed.
3. Hardware Secure Elements: Stores encryption keys in isolated memory regions.
4. Secure Data Partitioning: Separates sensitive user data from application logic to enhance security.

Key Capabilities and Achievements

This project demonstrates expertise in iterative hardware design, advanced LED technology, and secure electronics development.