Cc1200-balloon

cc1200-balloon

High altitude balloon payload: a CC1200 sub-GHz telemetry downlink and an air quality sensor stack, hosted by a Seeed Wio-E5 module. Four-layer 50 x 30 mm board, routed. The last full review is in BOARD_REVIEW.md; read its verdict table before ordering boards. Five items in it block fabrication.

The CC1200 radio and its 434 MHz matching network are carried over from the v1 design (an import of the Altus Metrum TeleMini netlist). Everything else is new: the Wio-E5 host, an AT6558R GNSS receiver with an on-board patch antenna and LNA, a burn/cutdown channel, and the sensor set from Forest-Balloon.csv.

Architecture

classDiagram
    direction LR

    class WioE5["U201 Wio-E5"] {
        STM32WLE5JC + SX126x
        SPI1 PB3 PB4 PB5
        I2C1 PB6 PB7
        USART2 PA2 PA3
        LPUART1 PC1
        ADC_IN0 PB13
        RFIO to J201 SMA
    }
    class Power["Power"] {
        J101 battery pads 3.6 V max
        Q101 reverse block
        +BATT unregulated
        R103 R104 sense divider
    }
    class Burn["Burn channel"] {
        Q1 P-FET high side
        gate on PA15
        J1 two pin header
    }
    class Radio["U301 CC1200"] {

Sheets

Power

There is no regulator and no switch. The cell drives the whole board through one P-channel FET:

J101 -- VBATT_IN -- Q101 (reverse block) -- +BATT -- everything

Q101 blocks a reversed cell: its source is on the load side, so the body diode conducts battery to load and the channel shorts it out. The rail is the cell minus one Rds(on) and follows the cell from full charge to cutoff. R103/R104 (100k/100k) put half of it on PB13 for the ADC.

Every supply window on this rail is tabulated in section 4 of the 2026-09-15 review; the BMV080 and the TCXO are the tight ones.

GNSS front end

The receiver sees a passive 15 x 15 mm ceramic patch (J401, The Antenna Company AC33154-1T) mounted on the back of the board, feeding an Abracon ALND-WB-0014 LNA (U402, 16 dB, 0.85 dB noise figure) on the front. ANT_BIAS powers the LNA, which puts the LNA's 5.3 mA above the chip's 2.5 mA antenna-detect threshold and switches it off with the receiver in sleep. C402 100 pF blocks DC into RF_IN; L402 6.8 nH is the series match at the chip.

L404 8.2 nH sits in series 0.87 mm from RFIN, which is the Abracon reference topology. BOARD_REVIEW.md items 4, 8, 17, 21 and 24 still concern this block.

Burn channel

Q1, a P-channel FET on PA15, switches +BATT into the two-pin header J1 for a cutdown wire. R205 100 k holds the gate at the rail while the MCU is in reset. Review items 15, 20, 22 and 23 still concern it.

Wio-E5 pin map

CC1200 GPIO0 and GPIO3 go to test pads TP301/TP302. GNSS SWD is on TP401/TP402.

Interfaces

Parts, data sheets and BOM

Most bought symbols carry Datasheet, MPN and Manufacturer fields, mirrored onto the board's footprints. The sourcing table is tools/parts.json.

python3 tools/set_part_fields.py --check   # report what would change
python3 tools/set_part_fields.py           # write fields into *.kicad_sch and the .kicad_pcb
python3 tools/gen_digikey_bom.py           # digikey_bom.csv, BOM.md, bom.json

The BOM tools do not currently run. Six symbols (Q1, J1, X401, U402, C416, J401) have no entry in tools/parts.json, so digikey_bom.csv and BOM.md are stale: they still list three SMA jacks, an off-board active antenna, the old TCXO and two BME688. Review item 19 lists the DigiKey numbers to add.

The generator is stale

sheets/*.json, build.sh and the TypeScript tools describe the design as it stood on 2026-09-06. The schematics were hand-edited after that and the board was routed against them. Do not run build.sh: it would overwrite all four sheets with the old design. The .kicad_sch files are the source of truth.

Verification

Known limitations

• The rail is unregulated and can touch 3.6 V, the absolute maximum operating supply of the Wio-E5 and the CC1200. Confirm the cell's open-circuit voltage before connecting it.
• No brownout floor. RF output power, the ADC reference and sensor readings drift with the cell. BATT_VSENSE makes the drift observable.
• The GNSS stops first. VDD_IO and DX_IN are specified from 2.7 V; the TCXO is rated to 3.3 V and is fed from a pin that can reach 3.6 V. Budget the flight on that, not on the cell's cutoff.
• The BMV080 wants 3.3 V +-5 % on its laser supply. On this rail it is in window only between 3.135 and 3.465 V.
• The patch antenna is characterized on a 50 x 50 mm ground plane and has 0.09 mm of it on one side here. Expect it to be off tune.
• GNSS altitude limit. The AT6558R data sheet says nothing about COCOM limits; confirm behavior above 18 km before flying.
• SCD40 in a balloon. Specified from -10 C and pressure dependent; compensate from the BME688 pressure channel.
• No thermal design, no antenna measurements. The CC1200 match values are TeleMini's; sweep them on this board.