Power Budget and Design Assumptions
Power architecture
- Input: 12 V AGM battery via external solar charge controller and fused battery line.
- PCB input: J_BAT -> reverse-polarity protection -> F1 5 A main fuse -> +12V_FUSED.
- +12V_FUSED derives +12V_PUMP, battery ADC divider, and +5V regulator input via F2 1 A logic fuse.
- 5 V regulator: TRACOPOWER TSR 2-2450, 5 V / 2 A.
- 3.3 V rail is provided by the ESP32-S3 development board header and powers I2C modules, BME280, I2C pull-ups, and the PNP sensor-power switch control.
- +3V3_SENSOR is a switched 3.3 V rail for eight soil sensors using BC32740TA PNP high-side switching.
Load budget used for sizing
- Pumps: board power path sized for 5 A total on +12V_PUMP, although firmware normally runs one pump at a time.
- Logic + sensors from +5V regulator: ESP32-S3 dev board peak assumed up to ~700 mA on 5 V input; two DFRobot SEN0204 water-level sensors are powered from +5V and are low-current sensor loads, assumed =5 A.
- D7 reverse-polarity protection is in the main 12 V path. If populated as a series Schottky diode, it must be a through-hole high-current Schottky rated for at least the 5 A pump-bus design current, with forward-voltage drop and heat dissipation verified before assembly. A future P-channel MOSFET ideal-diode option would reduce loss.
- D6 is the +12V_FUSED-to-GND TVS. Select a through-hole axial P6KE/1.5KE-style TVS with reverse standoff voltage above the maximum normal AGM charge voltage (~14.4 V), so it does not conduct during normal charging.
Assumptions to verify
- ESP32-S3 development board footprint is represented as dual female headers exposing: 5V/VIN, 3V3, GND, GPIO4, GPIO5, GPIO6, GPIO7, GPIO8, GPIO9, GPIO12-GPIO18, and GPIO21. Exact board mechanical pitch/spacing must be matched to the selected dev board before fabrication.
- DFR0553 ADS1115 modules are treated as external Gravity modules with I2C and analog channel connector pins on the carrier; their onboard pull-ups/address solder jumpers may exist and should be checked to avoid overly strong I2C pull-ups.
- The PCB remains low-voltage DC only; solar charge controller, panel, and AGM battery are external to this PCB.