While we are used to USB WiFi adapters, embedded devices typically use SDIO WiFi cards, and for good reasons – they’re way more low-power, don’t take up a USB port, don’t require a power-sipping USB hub, and the SDIO interface is widely available. However, SDIO cards and modules tend to be obscure and proprietary beyond reason. Enter ESP-Hosted – Espressif’s firmware and driver combination for ESP32 (press release)(GitHub), making your ESP32 into a WiFi module for either your Linux computer (ESP-Hosted-NG) or MCU (ESP-Hosted-FG). In particular, ESP-Hosted-NG his turns your SPI- or SDIO-connected ESP32 (including -S2/S3/C2/C3/C6 into a WiFi card, quite speedy and natively supported by the Linux network stack, as opposed to something like an AT command mode.

We’ve seen this done with ESP8266 before – repurposing an ESP8089 driver from sources found online, making an ESP8266 into a $2 WiFi adapter for something like a Pi. The ESP-Hosted project is Espressif-supported, and it works on the entire ESP32 lineup, through an SDIO or even SPI interface! It supports 802.11b/g/n and even Bluetooth, up to BLE5, either over an extra UART channel or the same SDIO/SPI channel; you can even get BT audio over I2S. If you have an SPI/SDIO port free and an ESP32 module handy, this might just be the perfect WiFi card for your Linux project!

There are some limitations – for instance, you can’t do AP mode in the NG (Linux-compatible) version. Also, part of the firmware has blobs in it, but a lot of the firmware and all of the driver are modifiable in case you need your ESP32 to do even more than Espressif has coded in – this is not fully open-source firmware, but it’s definitely way more than the Broadcom’s proprietary onboard Raspberry Pi WiFi chip. There’s plenty of documentation, and even some fun features like raw transport layer access. Also, of note is that this project supports ESP32-C6, which means you can equip your project with a RISC-V-based WiFi adapter.

Title image from [zhichunlee].

Displays are crucial to modern life; they are literally everywhere. But modern flat-panel LCDs and cheap 7-segment LED displays are, well, a bit boring. When we hackers want to display the progress of time, we want something more interesting, hence the plethora of projects using Nixie tubes and various incantations of edge-lit segmented units. Here is [upir] with their take on the simple edge-lit acrylic 7-segment design, with a great video explanation of all the steps involved.

The idea behind this concept is not new. Older displays of this type used tiny tungsten filament bulbs and complex light paths to direct light to the front of the display. The modern version, however, uses edge-lit panels with a grid of small LEDs beneath each segment, which are concealed within a casing. This design relies on the principle of total internal reflection, created by the contrast in refractive indices of acrylic and air. Light entering the panel from below at an angle greater than 42 degrees from normal is entirely reflected inside the panel. Fortunately, tiny LEDs have a wide dispersion angle, so if they are positioned close enough to the edge, they can guide sufficient light into the panel. Once this setup is in place, the surface can be etched or engraved using a CNC machine or a laser cutter. A rough surface texture is vital for this process, as it disrupts some of the light paths, scattering and directing some of it sideways to the viewer. Finally, to create your display, design enough parallel-stacked sheets for each segment of the display—seven in this case, but you could add more, such as an eighth for a decimal point.

How you arrange your lighting is up to you, but [upir] uses an off-the-shelf ESP32-S3 addressable LED array. This design has a few shortcomings, but it is a great start—if a little overkill for a single digit! Using some straightforward Arduino code, one display row is set to white to guide light into a single-segment sheet. To form a complete digital, you illuminate the appropriate combination of sheets. To engrave the sheets, [upir] wanted to use a laser cutter but was put off by the cost. A CNC 3018 was considered, but the choice was bewildering, so they just went with a hand-engraving pick, using a couple of 3D printed stencils as a guide. A sheet holder and light masking arrangement were created in Fusion 360, which was extended into a box to enclose the LED array, which could then be 3D printed.

If you fancy an edge-lit clock (you know you do) check out this one. If wearables are more your thing, there’s also this one. Finally, etched acrylic isn’t anywhere near as good as glass, so if you’ve got a vinyl cutter to hand, this simple method is an option.

When word first got out that the Chinese board houses were experimenting with full color silkscreens, many in our community thought it would be a boon for PCB art. Others believed it would be akin to cheating by removing the inherent limitations of the medium. That’s not a debate that will be solved today, but here we have an example of a project that’s not only making practical application of the technology, but one that arguably couldn’t exist in its current form without it: a single-PCB ZX Spectrum emulator developed by [atomic14].

There basics here are, well, they’re pretty basic. You’ve got an ESP32-S3, a TFT display, a micro SD slot, and the handful of passives necessary to tie them all together. What makes this project stand out is the keyboard, which has been integrated directly into the PCB thanks to the fourteen pins on the ESP32-S3 that can be used as touch sensor input channels. There are issues with detecting simultaneous keypresses, but overall it seems to work pretty well.

But what makes the keyboard really special is that [atomic14] has used the color silkscreen capability to put all the necessary labels directly onto the keys. Technically this could have been done using a traditional single color silkscreen, but it would have been a hell of a lot harder to fit all the necessary information on there while keeping it readable. Plus, you’d miss the little rainbow in the corner.

As good as it looks already, the project is still in the early stages of development. Some components, such as the TFT display, still need to be better integrated into the board. In terms of software, the board is running a ZX Spectrum emulator that [atomic14] developed previously. Judging by the gameplay in the video below, it’s doing a solid job of bringing this classic system (and its games) back to life.