Chat
Welcome to Flux
Treat Flux like your intern. Tell it what you'd like to build and it'll get to work. You can also ask it questions, brainstorm ideas, and teach it your preferences. Learn More
Explain project
Write a project description
Find schematic issues
Create a test plan
Simulate a circuit
Prepare for Manufacturing
Component Selection Workflow
New Subsystem Wizard
Write I2C initialization code
Generate firmware skeleton
Refine this doc
Ask about this doc
Design Notes
Conservative power-budget decision
Eight MG90S servos dominate the design. Because vendor/clone stall data vary, use 1.0 A per servo at 5 V as the conservative interface design point: 8 A simultaneous stall. Add 25% rail margin, yielding a 10 A minimum Buck #1 and connector rating. This is deliberately above typical walking current and prevents selecting a common 2–3 A module that would brown out or overheat.
Buck #1 and Buck #2 remain off-board regulated module interfaces. Their conversion circuitry is not placed on this schematic because exact module MPNs, thermal implementation, switching frequency, and verified transient ratings were not supplied.
Input reflection
At low battery (9.0 V) and 90% assumed conversion efficiency:
- Buck #1 at 5 V × 10 A: 50 W / (9.0 V × 0.90) = 6.17 A battery current.
- Buck #2 at 5 V × 5 A: 25 W / (9.0 V × 0.90) = 3.09 A battery current.
- Combined full interface rating: 9.26 A steady equivalent, before wiring/fuse margin.
Use a 15 A transient-capable battery connector/wiring path and an appropriately selected external fuse. Confirm pack C-rating and voltage sag experimentally.
Grounding and domains
All grounds are electrically common. Servo and LED return currents should use dedicated connector returns and converge at a low-impedance power entry region in layout; they must not flow through logic/audio return traces. Relay contacts switch LED +5 V only.
Safe startup
- PCA9685 OE has a 10 kΩ pull-up to 3.3 V so PWM outputs are disabled during reset.
- Relay IN1/IN2 each have 10 kΩ pull-ups to 3.3 V so active-low channels remain off during reset.
- Firmware drives relay pins HIGH before configuring them as outputs.
Open confirmations
- Actual MG90S manufacturer and measured stall current.
- LED strip voltage/current per meter and maximum connected length.
- Exact buck-module MPNs and connector family.
- Relay module input threshold/current and whether VCC/JD-VCC are separate.
Conservative power-budget decision
Input reflection
Grounding and domains
Safe startup
Open confirmations
