MAD documentation
Architecture
Power, firing, sensing and control in the Rev A design.
Rev A is prototype hardware and is not flight qualified. This page describes the design as drawn; it may change.
Power and firing
The JST-PH input passes through a resettable fuse and a reverse-polarity P-MOSFET. An LTC3115-1 buck-boost regulator produces the 5 V battery rail across the 3–18 V input range. USB VBUS and the battery regulator are diode-ORed into the 5 V system rail, and an AP2112K supplies 3.3 V logic.
The TPS61040 firing charger is intentionally supplied from the battery rail, so USB alone cannot charge the firing bank.
The firing bank is two 470 µF, 16 V capacitors at a nominal 12 V. Both the charge and fire commands pass through separate 74LVC1G08 AND gates whose second input is the physical ARM header. A low-side MOSFET switches the match. A 2.2 kΩ bleeder makes the bank decay when charging is disabled, but the voltage must always be verified before handling.
Sensing and control
The RP2040 reads an MMC5983MA magnetometer over I²C. The magnetometer occupies the nose end of the PCB inside an explicit inner- and back-copper keepout.
Orientation is the sole apogee cue. Voltage readings are safety interlocks and telemetry, not alternate apogee sensors.
ADC channels monitor battery voltage, firing-bank voltage and low-current continuity. An RGB LED reports state. A W25Q128 QSPI flash reserves a 4 MiB append-only flight-log region at the top of the device.
Connectors
| Connector | Function |
|---|---|
| J1 | Battery input, JST-PH: pin 1 positive, pin 2 ground |
| J2 | Electric match, 5 mm screw terminal |
| J3 | ARM jumper; remove whenever handling the output |
| J4 | USB-C device for configuration and logs, USB 2.0 full speed |
| J5 | SWD programming and debug |
GPIO map
| GPIO | Function |
|---|---|
| 0 / 1 | Magnetometer SDA / SCL |
| 2 | Magnetometer interrupt |
| 3 | ARM_PRESENT input |
| 4 / 5 | CHARGE_CMD / FIRE_CMD |
| 6 / 7 / 8 | RGB LED |
| 26 / 27 / 28 | Battery / capacitor / continuity ADC |
USB commands
The Rev A firmware answers three commands over USB:
| Command | Action |
|---|---|
STATUS |
Reports state, battery voltage, capacitor voltage and whether the ARM jumper is present |
DUMP |
Outputs the flight log |
ERASE |
Erases the flight log; refused while the ARM jumper is present |