An open ESP32-S3 handheld that combines RivetTX, ExpressLRS, an RX5808 receiver, an AT7456E OSD, and an AMT630A snow-screen display.

Why OpenPocket · Architecture · Hardware · Build path · Firmware · Documentation

Caution

OpenPocket is an engineering prototype, not a flight-proven product. Build the first revision on a current-limited bench supply. Keep propellers removed and mechanisms safe until your exact transmitter, failsafe, power system, RF link, and video chain have passed hardware-in-the-loop validation.

Why OpenPocket

OpenPocket puts the controls, live analog FPV picture, and transmitter menus in one compact handheld. It uses the existing RivetTX OpenPocket character compositor unchanged and connects it to a physical AT7456E video-overlay backend. The ESP32 never has to capture or process video pixels.

One handheld	Gimbals, switches, ExpressLRS control, telemetry, video, and menus in a single enclosure.
Purpose-built MCU	ESP32-S3 provides the GPIO, native USB, and task separation needed by the complete controller.
Low-latency video	RX5808 composite video passes through the AT7456E into an AMT630A TFT controller without digital capture.
Snow-screen display	The selected AMT630A board keeps weak or lost analog video visible as noise instead of hiding it behind a blue screen.
Native analog OSD	PAL/NTSC autodetection, a 30×16 character grid, custom glyphs, delta updates, and video-loss recovery.
Bounded background work	OSD and receiver services cannot delay control, CRSF, or telemetry processing.
Open development path	Wiring, BOM decisions, bring-up evidence, and future KiCad sources live in this repository.

Architecture

The flight-control path stays short while video and presentation work run as bounded services.

flowchart LR
    A[Gimbals + switches] --> B[ESP32-S3<br/>RivetTX]
    B --> C[CRSF UART]
    C --> D[ExpressLRS<br/>TX module]

    E[5.8 GHz antenna] --> F[RX5808]
    F -->|composite video| G[AT7456E]
    G -->|video + overlay| H[AMT630A<br/>snow-screen board]
    H --> I[Matched TFT panel]

    B -->|tune + RSSI| F
    B -->|bounded SPI| G
    D -->|telemetry| B

    classDef control fill:#102a43,stroke:#38bdf8,color:#f8fafc;
    classDef video fill:#26163f,stroke:#a78bfa,color:#f5f3ff;
    class A,B,C,D control;
    class E,F,G,H,I video;

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The 250 Hz control task owns channel output and safety. The OSD driver advances a non-blocking state machine and writes only changed character runs. Video loss, PAL/NTSC changes, or an absent OSD chip must never hold up the control path.

Hardware

Component	Role
ESP32-S3 development board or module	RivetTX, inputs, UI, storage, USB, and hardware services
ExpressLRS TX hardware	full-duplex 3.3 V CRSF control and telemetry link
RX5808 module	tunable 5.8 GHz analog receiver, composite video, and RSSI
AT7456E OSD module	PAL/NTSC character overlay between the receiver and display
AMT630A snow-screen controller board	PAL/NTSC composite decoding without blue-screen signal masking
matched parallel-RGB TFT panel	live FPV image and the complete OpenPocket interface
two dual-axis gimbals	four primary analog control axes
switches, menu buttons, and optional encoder	arming, AUX controls, navigation, and editing
validated regulators and protection	clean supplies sized for RF, display, video, and logic peaks

The ESP32-S3 is the OpenPocket target. RivetTX may support smaller ESP32-C3 transmitters, but the C3 is not the reference platform for this handheld. See ADR-0001 for the decision record.

Analog OSD

The existing RivetTX compositor produces a hardware-independent 30-column by 16-row character frame. The AT7456E backend then provides:

• PAL/NTSC autodetection and safe standard changes without a reboot
• all 30×16 cells in PAL, with essential content held inside 30×13 for NTSC
• custom character uploads for icons, selection markers, and warnings
• shadow-frame comparison so unchanged cells generate no SPI traffic
• bounded asynchronous transfers instead of full-screen blocking redraws
• communication retry/backoff and redraw after video loss or recovery

The RX5808 feeds baseband video to the AT7456E; the AT7456E overlays text and passes the result to the AMT630A board, which drives its matched TFT panel. The AMT630A's internal OSD is not used for OpenPocket menus. See the complete wiring guide.

Build path

Bring up one subsystem at a time:

1. Read the bill of materials and record the exact revisions of every module.
2. Build and measure the protected 5 V and 3.3 V rails on a current-limited supply.
3. Add the ESP32-S3, controls, and ExpressLRS link with RF output constrained.
4. Prove the direct RX5808-to-AMT630A composite path in PAL and NTSC, including snow-screen behavior with no received signal.
5. Insert the AT7456E, level shifting, and SPI control lines.
6. Configure RivetTX, then complete every item in the bring-up checklist.

The bench build guide contains the full sequence and stop conditions. Do not design a battery pack or order a PCB production run from the provisional module-level BOM.

Firmware

OpenPocket runs the main branch of Twotoz/RivetTX:

git clone https://github.com/Twotoz/RivetTX.git
cd RivetTX
idf.py set-target esp32s3
idf.py menuconfig
idf.py build
idf.py flash monitor

Enable Use OpenPocket AT7456E analog OSD instead of SSD1306 under Component config -> RivetTX hardware, then assign pins for the OSD, CRSF, controls, and other peripherals. There is deliberately no universal GPIO map until a specific ESP32-S3 module and reviewed schematic are selected. See the firmware guide for the complete configuration.

Documentation

Document	Contents
Bill of materials	prototype parts, electrical requirements, and unresolved selections
Wiring	ESP32-S3, RX5808, AT7456E, AMT630A, TFT, and ExpressLRS interconnects
Bench build guide	staged assembly sequence and stop conditions
Firmware	ESP32-S3 target setup and RivetTX OSD configuration
Bring-up checklist	electrical, control, PAL/NTSC, failure-recovery, and endurance tests
Architecture	task boundaries, character presentation, and video path
ESP32-S3 decision	why OpenPocket standardizes on the S3
AMT630A display decision	why the display stage uses a snow-screen AMT630A board
Hardware sources	scope and release policy for future KiCad and production files

Project status

RivetTX already contains the 30×16 OpenPocket menus and the physical AT7456E backend, including host-side PAL, NTSC, navigation, warning, delta-update, glyph-upload, video-loss, standard-change, and SPI-failure tests. RX5808 target hardware, the exact AMT630A PCB/panel revision, the final GPIO assignment, the reference schematic, PCB, power system, and complete composite-video HIL evidence remain open engineering work.

No schematic, PCB, enclosure, or battery design is currently released as production-ready. The hardware directory will become the authoritative source for those files after design review and measurement.

Contributing

Issues, schematic reviews, module measurements, and focused pull requests are welcome. Hardware findings must identify the exact module revision, voltage, firmware commit, measurement point, and PAL/NTSC source. See CONTRIBUTING.md.

License

OpenPocket documentation and future hardware sources are released under the MIT License. RivetTX is maintained in its own repository under its own license.

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_{Built for open hardware experimentation, low-latency analog FPV, and careful validation.}