See How Clem Mayer Took His Unique USB Card Reader Project From Idea to Prototype

The creation process

Every project/product has to start with an idea, but going from that initial step all the way to a functioning prototype can be a very intimidating process to navigate, especially for beginners. As a way to helper clarify what needs to happen when taking the leap from idea to tangible product, element14 Presents host Clem Mayer undertook a project to build his own USB card reader with relatively common components and a DIY PCB design.

Finding a product

Before one can even find an idea for something to build, innovation and brainstorming can often take the form of looking at already existing products and imagining the ways in which they could be improved. Mayer's source of inspiration was his old USB/SD card hub that would constantly disconnect due to faulty connectors and was difficult to use thanks to its non-ideal form factor. To iterate, he thought of taking the USB hub idea, flattening the design into a thin card shape while adding USB-C functionality, and include a full-size SD card for ease-of-use.

The PCB and enclosures

According to Mayer, it is a wise idea to incorporate existing components into a design and possibly use separate ICs for various tasks rather than monolithic ones, at least initially, to eliminate points of failure. In this design, he went with a USB2640 USB hub + media controller IC from Microchip which combines the USB functionality and ability to read/write SD cards into a single chip. In addition to this component, Mayer added an ESP32-C3 to adjust the amount of current being provided by the external micro USB port, two USB-C ports for data and power, and dual ESD protection circuits for future use.

Since reliable 3D-printed enclosures can be a challenge to both design and fabricate, Mayer points out how there is already large ecosystem of pre-made enclosures available. With the sizes known in advance from their datasheets, PCBs can be designed to fit nicely and custom face plates can be made for port openings and added protection.

Challenges with a proof of concept

After assembling his USB card reader circuit, Mayer plugged in the USB-C port to his PC and discovered nothing was being recognized because the connector was not soldered properly. After a quick fix, it still was not working, this time due to a missing bias resistor. Once added, the media controller chip was finally being enumerated by the OS, yet the ESP32 chip was still not recognized due to, again, improper reflowing thanks to too many nearby heatsinks.

Opportunities for improvements

All of these problems and eventual solutions are a natural part of the iterative design process, and each lesson along the way leads to a far better product in the end. As Mayer emphasizes in his video, carefully reading the datasheet, double-checking footprints, and adding plenty of test points are all important steps to ensuring things work the first time. For his next iteration, Mayer plans to fall back to a previous USB/media controller chip, SD card slot, and voltage regulation circuit since they are more familiar.

To see more about how this USB card reader was designed/built and the challenges along the way, you can watch Mayer's e14 Presents video below!