Motor Controller for a Robot Arm
Worked for 4 mins 36 sec
Created 2 project docs
Board Bring-Up Plan — Closed-Loop DC Motor Controller
Equipment: current-limited bench supply, DMM, oscilloscope, ST-LINK/SWD debugger, USB-UART adapter, encoder simulator or known encoder, dumm...
Implemented and verified the schematic for the closed-loop brushed DC motor controller.
What was completed:
- Added a robust 12 V nominal motor-controller architecture: MC33926 H-bridge, STM32G431 MCU, INA240 current sense, LMR33630 3.3 V buck, LM74700 reverse protection, encoder conditioning, connectors, LEDs, and protection.
- Wired power, motor drive, current sensing, encoder A/B/Z, SWD, UART control, reset/BOOT0, and fault/status paths.
- Ran schematic/ERC checks; there are no open ERROR/WARNING/UNCERTAIN checks in the reviewed schematic categories.
Project files created/updated:
Open items:
- Layout is not started yet; high-current motor paths, shunt Kelvin routing, buck layout, and thermal copper will be critical.
- Firmware starter is a HAL bring-up baseline; final PID/current-limit tuning still needs motor characterization.
Suggested next steps:
- Set PCB constraints: board size, stackup, current-aware trace widths, and clearance rules.
- Place components with power path and thermal priorities.
- Route the PCB, then run DRC/PI checks.
- Add test points for 3V3, VM_PROT, HBRIDGE_EN, current sense, and encoder signals.
Set constraints and layout
Set PCB constraints
Place components
Route the PCB
Add test points
Review BOM risks
Refine this doc
Ask about this doc
Board Bring-Up Plan — Closed-Loop DC Motor Controller
Prerequisites
- Equipment: current-limited bench supply, DMM, oscilloscope, ST-LINK/SWD debugger, USB-UART adapter, encoder simulator or known encoder, dummy resistive load or lamp load, thermal camera or IR thermometer.
- Firmware: see Firmware Starter — STM32G431CBT6.
- Safety: first power-on must be from a bench supply, not a battery. Do not connect the final motor until power, default-disabled H-bridge behavior, current sense, and firmware current limiting are verified.
1. Visual Inspection
- Inspect U2 MC33926 thermal pad/power pins, U3 LMR33630 buck area, U5 LM74700/Q1 reverse-protection orientation, U4 INA240, R13 shunt, and all connector solder joints.
- Confirm J1 polarity: PIN1 = VIN_IN positive input, PIN2 = GND.
- Confirm J2 motor output is isolated from GND and VM_PROT except through the intended H-bridge paths.
2. Power Rail Verification
Table
| Rail | Source | Expected Voltage | Tolerance | Measure At | Current Limit | Pass Criteria |
|---|---|---|---|---|---|---|
| VIN_IN | J1 pin 1 | Applied input, start 3-5 V then 12 V nominal | Supply setting | J1/F1 input | 50-100 mA first power | No short/current-limit hit |
| VIN_RAW | F1 output / input TVS / LM74700 anode | Approximately VIN_IN after PTC | Depends on PTC drop | F1 P2 or U5 ANODE | 50-100 mA first power | Tracks input with correct polarity |
| VM_PROT | LM74700/Q1 protected bus | Approximately VIN_RAW minus MOSFET drop | <100 mV drop at light load | U5 CATHODE, U3 VIN, U2 VPWR | 50-100 mA first power | Comes up only with correct input polarity |
| 3V3 | U3 LMR33630 buck output | 3.3 V | +/-5% initial | C9-C12/C32 or U1 VDD | Logic-only <250 mA expected | 3.135-3.465 V, no oscillation |
| BUCK_SW | U3 SW/L1 | Switching waveform | N/A | U3 SW or L1 P1 | Probe only | Regular switching, no overheating |
| MOTOR_A/MOTOR_B | U2/J2 | Hi-Z while disabled | N/A | J2 pins | No motor connected | No unintended drive during reset |
Procedure:
- With power off, measure resistance: VIN_IN-GND, VIN_RAW-GND, VM_PROT-GND, 3V3-GND, MOTOR_A-GND, MOTOR_B-GND, and MOTOR_A-MOTOR_B.
- Apply 3-5 V with 50-100 mA current limit and no motor connected.
- Verify VM_PROT and 3V3. Increase input to 8 V, then 12 V only if current draw is normal.
- Scope 3V3 ripple and BUCK_SW; stop if 3V3 is out of tolerance or U3 heats.
- Verify U2 stays disabled through MCU reset and firmware boot.
3. Critical Signal Verification
Table
| Signal | Net | Expected State | Measure At | Notes |
|---|---|---|---|---|
| Reset | NRST | High at idle, low when SW1 pressed | U1 PG10-NRST or J4 pin 5 | SWD reset also uses this net |
| Boot strap | BOOT0 | Low | U1 PB8 / R4 | Normal flash boot |
| H-bridge enable | HBRIDGE_EN | Low until firmware arms | U2 EN / U1 PB5 | R12 pull-down is safety default |
| Disable D1 | HBRIDGE_D1 | Low at reset | U2 D1 / U1 PA10 | High disables bridge |
| Disable D2_N | HBRIDGE_D2_N | High at reset | U2 | Low disables bridge |
| Fault | HBRIDGE_FAULT_N | High when no fault | U2 | Active-low open drain via R7 |
| Current zero | MOTOR_CURRENT_ADC | About 1.65 V at zero motor current | R14/C27/U1 PA1 | INA240 REF1=3V3, REF2=GND |
| Power-good | PWR_GOOD | High when 3V3 valid | U3 PG / U1 PB12 | R3 pull-up to 3V3 |
4. Connector and Interface Tests
Table
| Connector | Type | Pins to Verify | Test Method |
|---|---|---|---|
| J1 | 2-pin power terminal | PIN1 VIN_IN, PIN2 GND | DMM continuity and polarity mark check |
| J2 | 2-pin motor terminal | PIN1 MOTOR_A, PIN2 MOTOR_B | DMM continuity to R13/U2 outputs; no short to GND |
| J3 | 6-pin encoder header | 3V3, GND, ENC_A_RAW, ENC_B_RAW, ENC_Z_RAW, GND/shield | Apply slow 0-3.3 V pulses; verify U6 outputs and MCU timer count |
| J4 | 2x3 SWD | 3V3, SWDIO, SWCLK, GND, NRST, SWO | ST-LINK target detect/read ID |
| J5 | 1x4 control UART | 3V3, GND, UART_TX, UART_RX | 115200 baud UART telemetry and echo/control test |
5. Programming and Debug Interface
Table
| Interface | Signals | Connector | Tool |
|---|---|---|---|
| SWD | 3V3, SWDIO, SWCLK, NRST, GND | J4 | ST-LINK / STM32CubeProgrammer |
| UART telemetry/control | UART_TX, UART_RX, GND | J5 | USB-UART at 3.3 V logic |
Procedure:
- Power at 12 V current-limited with no motor.
- Connect ST-LINK to J4 and verify target detection.
- Read MCU device ID.
- Flash safety firmware with HBRIDGE_EN held low by default.
- Confirm UART telemetry on J5.
6. Functional Validation
Table
| Test | Components | Input | Expected Output | Pass Criteria |
|---|---|---|---|---|
| Power LED | U3, LED1/R21 | 3V3 valid | LED1 on | LED current limited, no overheating |
| Heartbeat LED | U1, LED3/R23 | Firmware running | LED3 toggles | Confirms MCU boot loop |
| Fault LED | U1, LED2/R22, U2 SF | Simulated fault or firmware command | LED2 changes | Fault input readable |
| Encoder | J3, D3, R15-R20, C28-C30, U6, U1 TIM3 | Slow A/B quadrature pulses | Encoder count changes | Direction and count correct |
| Current sense | R13, U4, U1 ADC | Dummy load current | ADC matches DMM within calibration tolerance | Zero-current around 1.65 V |
| H-bridge no-load PWM | U1/U2 | Firmware low-duty command, no load | MOTOR_A/MOTOR_B switch as expected | Truth table matches MC33926 |
| Dummy load drive | U2/R13/U4 | 10-50 ohm power resistor or lamp | Controlled current and PWM | No current-limit trip, no overheating |
| Real motor | U2/J2 | Final motor unloaded, low duty | Smooth rotation and valid encoder feedback | Current below configured limit |
7. Expected Measurements Reference
Table
| Measurement | Location | Expected Value | Tolerance | Instrument |
|---|---|---|---|---|
| 3V3 rail | C32/U1 VDD | 3.3 V | +/-5% initial | DMM/scope |
| INA240 zero output | C27/R14 | ~1.65 V | +/-100 mV before calibration | DMM/ADC |
| R13 shunt voltage at 2 A | R13 Kelvin pads | 20 mV | Depends on load | DMM/scope |
| INA240 output swing at 2 A | MOTOR_CURRENT_ADC | +/-0.4 V from 1.65 V | After calibration | ADC/scope |
| MC33926 FB at 2 A | HBRIDGE_FB_ADC | ~1.30 V with 270 ohm R6 | Approximate, coarse feedback | ADC/DMM |
| HBRIDGE_EN reset state | U2 EN | 0 V | Logic low | Scope/DMM |
| HBRIDGE_FAULT_N no-fault | U2 SF | 3.3 V | Logic high | Scope/DMM |
8. Motor-Specific Precautions
- Use no-load and dummy-load tests before a real motor.
- Do not rely on F1 PTC for fast motor current limiting; implement firmware current limit first.
- Watch VM_PROT during deceleration/braking because regenerative energy can pump the bus above the bench supply setpoint.
- Avoid aggressive braking and reversal until TVS heating and bus overshoot are validated.
- Start final motor at low voltage, low duty cycle, and no mechanical load.
Pass/Fail Summary
Table
| Test Section | Result | Notes |
|---|---|---|
| Visual Inspection | [ ] Pass / [ ] Fail | |
| Power Rails | [ ] Pass / [ ] Fail | |
| Critical Signals | [ ] Pass / [ ] Fail | |
| Connectors | [ ] Pass / [ ] Fail | |
| Programming | [ ] Pass / [ ] Fail | |
| Encoder | [ ] Pass / [ ] Fail | |
| Current Sense | [ ] Pass / [ ] Fail | |
| Motor Drive | [ ] Pass / [ ] Fail |
Board Status: [ ] Ready for controlled motor test / [ ] Requires rework
Prerequisites
1. Visual Inspection
2. Power Rail Verification
3. Critical Signal Verification
4. Connector and Interface Tests
5. Programming and Debug Interface
6. Functional Validation
7. Expected Measurements Reference
8. Motor-Specific Precautions
Pass/Fail Summary
