A3-before crystal refinement

ESP32 + CC1101 Multiband

A custom USB-C development board combining an ESP32-WROOM-32E-N8 with an integrated CC1101 sub-GHz radio, software-selected RF paths, and a vertical SMA antenna connector at the opposite end from USB-C.

Rev A3 · Fully connected review candidate · Not approved to manufacture or sell

The aim is to replace a separate ESP32 board, CC1101 breakout and jumper wires with one purpose-built PCB. The first intended build is five assembled engineering prototypes, after the pre-order checks are complete. Possible product sales are a future option, not a launch announcement.

Current design

KiCad design render—not a photograph of a built board. USB, SMA and some RF parts lack complete 3D bodies. Their absence in the image does not mean they were removed from the design.

Top view and experimental routing

The routing image is a separate experimental candidate, not the main placement file or a fabrication package. Bottom and inner routes are not shown here.

Schematic SVG · Latest design report · Draft BOM · Roadmap

Latest work: A3 replaces the power supply and RF switches, completes routed connectivity, adds safe RF boot sequencing and proposes all populated parts. See engineering decisions and first-power instructions and the pre-order blocker report. The crystal was relocated and rerouted: all 180 artifact checks and six route screens now pass. Independent/supplier reviews remain pending. No hardware has been tested. Do not order historical A2 files.

Building blocks and design inputs

ESP32-WROOM-32E-N8 — controller and 2.4 GHz connectivity

Stock module reference image: Espressif, linked from the manufacturer's site. This is not a photo of the custom board or a guarantee of the N8 marking.

The actual component is an Espressif module, not an entire stock development board soldered onto another PCB. The selected N8 variant has 8 MB flash; its ESP32 provides a dual-core processor, 2.4 GHz Wi-Fi and Bluetooth. Its PCB antenna is separate from the sub-GHz SMA path. The antenna section extends beyond the custom base board to preserve its keepout. Module datasheet.

Power/programming uses ESP32 development-board conventions: USB-to-UART, automatic reset/boot control and manual BOOT/RESET buttons. This is not a pin-compatible clone of a particular commercial DevKit. Espressif ESP32-DevKitC reference.

Texas Instruments CC1101 — sub-GHz transceiver

Representative package image: Texas Instruments. This is the IC package, not a complete CC1101 antenna module; package markings may differ.

The PCB integrates CC1101RGPR directly, with its crystal, bypass capacitors, balun, switches and matching/filter components. TI specifies tuning ranges of 300–348, 387–464 and 779–928 MHz. That does not make every frequency or antenna equally usable or establish this board's RF performance. CC1101 product information and datasheet.

The separate Amazon CC1101 module supplied by the owner was a functional starting point. Its exact internal circuit and advertised four-band performance have not been independently verified here. The switched RF topology and initial component values also reference the M5Stack Cap CC1101 schematic. This is a different implementation, not an endorsed M5Stack product.

Supporting parts currently selected

See third-party notices for provenance, image credits and license boundaries. Parts remain subject to sourcing, footprint and assembly approval; the BOM is not an approved shopping list.

Planned capabilities and features

Band switching changes the hardware path. Future firmware must also set the radio frequency/modem registers and operating limits. One CC1101 cannot listen on all four bands simultaneously. Use an antenna suitable for the selected band; a shared SMA does not imply a universal antenna.

There is no native USB, USB-PD, battery charger, finished RF application or guaranteed protocol compatibility in this revision.

What has actually been checked?

Snapshot: 2026-09-26, KiCad 10.0.6. Design-file checks, not lab results.

Zero reported violations does not prove working or compliant hardware. A3's power redesign addresses the earlier LDO heat problem and the new switches cover the target bands in their specified frequency range. Actual power sequencing, temperature, impedance, matching and crystal startup/frequency remain unmeasured. C21 and U5 contain in-pad vias requiring filled/capped processing; supplier DFM confirmation is mandatory. USB power must be configured before fitting J4, and full combined Wi-Fi/radio load is not approved.

Raw reports · Verification checklist · Power, routing and RF validation plan

Roadmap

1. Design capture — substantially complete: schematic, placement, draft BOM, local footprints, bring-up firmware and automated checks.
2. Prototype review — in progress: routed connectivity and proposed parts complete; crystal, power, mechanical, supplier and independent review open.
3. Five-board build — not ordered: reviewed fabrication and assembly files, then separately approved prototype procurement.
4. Bench and RF tuning — not started: power/temperature, USB, crystal, per-band matching, harmonics and receive performance.
5. Firmware/application — planned: validated receive-first operation, controlled band changes and deliberately configured regional limits.
6. Possible product — undecided: hardware revision, compliance, enclosure, test fixtures, sourcing, support and commercial terms.

The detailed roadmap uses acceptance criteria, not promised dates. There is no release date, sales price, preorder or claim of certification.

Open the project

Open hardware/esp32-cc1101-multiband.kicad_pro in KiCad 10 for the main placement seed and schematic. Open hardware/A3-routing-candidate.kicad_pro separately for the unapproved routing experiment. Do not order either one.

Python generators are the editable source for this checkpoint. Regenerating placement overwrites the generated board; preserve manual routing first. See rebuild instructions and firmware instructions.

Initial firmware resets the CC1101, checks repeated PARTNUM/VERSION reads and stable IDLE state, and logs explicit failures. It does not configure a receiver or transmitter and has not run on physical hardware. Passing digital diagnostics is not proof of authenticity or RF qualification.

AI disclosure

This project is developed with substantial assistance from OpenAI Codex under the owner's direction. AI assisted with component research, schematic/PCB generators, footprints, experimental routing, firmware, documentation and review. Design images are KiCad renders/exports, not AI-generated product photographs.

AI output and automated checks can contain errors. They are not independent engineering approval, bench validation or regulatory certification. No physical prototype has been completed. Qualified human electrical/RF review remains a release gate. See the full AI disclosure.

Licensing, commercial plans and safety

This initial publication uses the Public Review License: non-commercial study/private evaluation is permitted; manufacturing, product sales and other uses beyond its limited permissions require written permission. Commercial rights are reserved while the owner's plans are undecided. This is source-available, not open-source/open hardware. Third-party terms are separate; see notices. Obtain legal advice before relying on the custom license for a commercial launch.

Use only with equipment and signals you own or are authorized to test. Tunable frequencies are not automatically permitted transmit frequencies. Final use and sale require applicable RF, EMC, product-safety and other compliance work. This prototype is not for safety-critical applications. No manufacturer named here endorses the project.