AZB-12 AN-07 · wit.notazizelse.xyz

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Application note AN-07 · U7

WIT stratospheric payload

2026 · wit.notazizelse.xyz
ABSTRACT

The design package for a 3U stratospheric balloon payload, for a Women in Tech Uzbekistan project. Seven science missions, one 4-layer board with an STM32F407, two LoRa radios, a Geiger counter, a power budget, a test plan and a 91-byte telemetry packet.

All of it was planned before opening KiCad. Every part has a written reason, and so does every part that wasn't picked.

Drawing of a balloon, parachute and 3U payload with a radio link to a ground station, plus the list of seven missions
Figure 1.Balloon, parachute, payload, and the seven missions.

1Key Specifications

Envelope
3U, 100 × 100 × 300 mm
Board
4 layers, ENIG, about 90 × 90 mm
MCU
STM32F407VET6
Radios
MicoAir LR900-A and Ebyte E22-900T22S, on separate UARTs
Power
4 × Energizer L91 lithium AA, rated to −40 °C
Radiation
CAJOE board with an SBM-20 tube
Cost
About $211 per assembled board, about $2,300 for the whole project

2Functional Block Diagram

  1. sense7 missions' sensors
  2. computeSTM32F407
  3. log91-byte telemetry packet
  4. radio2 × LoRa
  5. groundground station
Figure 2.How WIT stratospheric payload works, left to right

3The seven missions

  • Upper-air profile over Uzbekistan
  • Air quality in the boundary layer over Tashkent
  • Cosmic radiation dose from the ground to burst
  • UV irradiance and ozone against altitude
  • GNSS availability and accuracy against altitude
  • LoRa link budget against range and altitude
  • How ordinary memory chips survive the flight

4What's next

Schematic capture, then the 4-layer layout. Long-lead parts get ordered in parallel so nothing waits on shipping.

5Technical Documents

AN-07-D1Overview and decisionsEverything decided so far, the costs and what's blocking.Read →AN-07-D2Mission definitionsHypothesis, expected graph, how it could fail, for each mission.Read →AN-07-D3Why each partAnd why not the alternatives.Read →AN-07-D4Parts list v2 changesRead →AN-07-D5Stackup and layout4-layer stackup, floorplan, grounding, RF routing.Read →AN-07-D6Firmware architectureRead →AN-07-D7Telemetry packet91 bytes, the single source of truth.Read →AN-07-D8Mechanical constraintsRead →AN-07-D9Test planFrom before first power to flight day.Read →AN-07-D10Where to buy everythingTashkent shops, distributors, AliExpress, JLCPCB.Read →AN-07-D11My 2-layer to 4-layer learning pathRead →

6Design Files

7Source