Rocket Dual-Deploy Flight Computer

You are the avionics lead on Altair Rocketry Club, a fictional student team preparing a single-stage sounding rocket for a national technology competition. The airframe carries two pyrotechnic charges: the first separates the payload bay, the second deploys the main parachute a moment later. Once the rocket leaves the pad it cannot be sent commands (the ground station only receives telemetry), so firmware alone decides both events, from the accelerometer and a millisecond timer. This revision shipped without a working barometric altimeter.

Hardware

• STM32F407 flight controller; startup initializes I2C1 and UART4 (TX only) before calling userCode().
• LIS2DS12 3-axis accelerometer on I2C1. Address, register map, conversion: Datasheet tab.
• Charge 1 (payload separation) on PD4, charge 2 (parachute) on PD12; startup does not configure port D. Both idle low; firing a charge means driving its line high and leaving it high.
• Telemetry goes out on UART4. This board reaches the accelerometer only over I2C1; SPI transmit/receive calls are not available on this hardware and are rejected before the submission builds.
• The breakout ships loose: connecting it is part of the job (see Wiring below).