Alex
A standard paper business card feels like a missed opportunity when you can build cool hardware instead.
My goal for this project was to pack an ESP32, microphone, and 40-pixel LED matrix onto a PCB the size of a business card with ability to display an audio visualizer.
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This project was made possible by NextPCB, who fabricated and assembled the boards.
They offer great promotions for prototyping and assembly.
Check out their services for your next project: https://www.nextpcb.com/?code=GopnikEnterprises
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The hardware is simple.
The board is powered via USB-C, which is regulated to 3.3V for the ESP32.
I routed the LED matrix in a snake pattern to keep the layout as clean as possible.
One difficulty that I wasn't expecting was finding a suitable microphone.
When I was designing the board a month or so ago, many of the common I2S microphones were not available.
I ended up going with the MSM261DGT003, which is a digital PDM microphone.
The WS2812C-2020-V1 LEDs require a 5V logic level, so added an SN74AHCT125DR to shift the 3.3V control signal from the ESP32 to 5V.
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The back side of the board has 2 QR codes, one to my LinkedIn and the other to my portfolio site.
It also has my social media info.
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The ESP32 handles real-time audio sampling and hosting a local web server for control.
There are 2 main audio visualizer modes:
- A scrolling waveform that calculates the RMS voltage of the audio blocks to display volume.
- A spectrum analyzer that runs a 256-sample Fast Fourier Transform to split the audio into 8 frequency bands that are mapped to the 8 x 5 LED matrix.
The firmware hosts an asynchronous web server and sets up the ESP32 as a standalone Wi-Fi Access Point.
When you connect to the card's network on a phone, you can access the control panel.
From there, you can swap between the audio modes, an ambient breathe effect, a solid color picker, and custom scrolling text.
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NextPCB did an amazing job on this board.
The whole process was smooth and the matte black soldermask looks really good.
If you're designing PCBs and want a manufacturing service that handles everything from prototypes to fully assembled boards at an affordable price, check out the link below: