I want a simplest possible schematic that allows m...

flux

I’ll check suitable AA battery-holder options, then update the schematic so the battery pack is the 9V input source and verify the power ERC afterward.

flux

Yes — for the existing 9V motor rail, the right AA approach is six AA cells in series. I didn’t find a single 6×AA holder in the library, so I’m using a 4×AA holder plus a 2×AA holder wired in series for 9V nominal alkaline output.

flux

Implemented the AA battery power update: added BT1 4×AA + BT2 2×AA in series as a 6×AA pack, wired to V9_MOTOR/GND through restored battery input terminal J2, and kept the holders as external/off-board parts. Updated the project files and verified ERC plus key placement/DRC checks are clean.
Open items:
  • 6× alkaline AA = ~9V nominal; 6× NiMH AA = ~7.2V nominal, so 9V motors may run slower on rechargeables.
  • Confirm motor stall current and AA cell discharge capability before relying on four motors at once.
Suggested next steps:
  1. Add an input fuse/polyfuse for battery short-circuit protection.
  2. Add reverse-polarity protection for the battery input.
  3. Re-check layout/routing with the restored J2 battery connector.
Add protections and verify
Add input fuse
Add reverse protection
Check battery current
Re-check layout
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Files

Schematic

Layout

Preview

Board Bring-Up Plan — Remote Pico Controller
Prerequisites
  • Current-limited bench supply capable of simulating the 6xAA pack, plus the actual 6xAA battery pack for later testing.
  • Multimeter and oscilloscope.
  • USB cable for Raspberry Pi Pico firmware upload.
  • Firmware from the Firmware Starter project file.
  • Do not connect motors during first power-on.
1. Visual Inspection
  • Confirm U2, U3, U1, Q1–Q4, and D1–D4 orientations.
  • Verify diode cathodes (D1–D4) connect to V9_MOTOR and anodes connect to motor low-side nets.
  • Check screw terminal polarity labels before applying power.
  • Inspect TO-220 MOSFET soldering and clearance around high-current paths.
2. Power Rail Verification

Table

RailSourceExpected VoltageToleranceMeasure AtInitial Current LimitPass Criteria
V9_MOTOR6xAA pack via J29V alkaline nominal / 7.2V NiMH nominalBattery chemistry dependentJ2:1 to GND100mA no-load bench supply firstNo short; rail follows supply/battery voltage.
V5U2 buck5.0V±5%J1:VSYS, C3:P1, C6:P1250mA no-load4.75V–5.25V.
V3V3_WIFIU3 AP21123.3V±3% typicalU1:VCC, C8:P1, C9:P1250mA no-load3.20V–3.40V.
Procedure:
  1. With power off, measure resistance from V9_MOTOR, V5, and V3V3_WIFI to GND.
  2. Apply a bench-supply equivalent of the intended battery pack at J2 with 100mA current limit and no motors installed.
  3. Measure V9_MOTOR, V5, and V3V3_WIFI.
  4. Increase current limit only after rails are correct.
  5. Check V5 ripple at C3 with oscilloscope.
3. Critical Signal Verification

Table

SignalNetExpected StateMeasure AtNotes
ESP enableESP_ENHigh, about 3.3VU1:ENPulled up by R1.
ESP resetESP_RSTHigh, about 3.3VU1:RSTPulled up by R2; active low.
ESP GPIO0 bootESP_GPIO0_BOOTHigh, about 3.3VU1:IO0High for normal boot.
ESP GPIO2 bootESP_GPIO2_BOOTHigh, about 3.3VU1:IO2High for normal boot.
Motor gatesMOTORx_GATELow at bootQ1–Q4 gates47k pulldowns should hold MOSFETs off.
4. Connector and Interface Tests

Table

ConnectorTypePins to VerifyTest Method
J1Pico socket/footprintVSYS, GND, GP0, GP1, GP18–GP21Continuity to named nets.
J29V input screw terminalPin 1 = V9_MOTOR, pin 2 = GNDPolarity and resistance check.
J3Motor 1 screw terminalPin 1 = V9_MOTOR, pin 2 = MOTOR1_LOWContinuity; no motor on first power-on.
J4Motor 2 screw terminalPin 1 = V9_MOTOR, pin 2 = MOTOR2_LOWContinuity.
J5Motor 3 screw terminalPin 1 = V9_MOTOR, pin 2 = MOTOR3_LOWContinuity.
J6Motor 4 screw terminalPin 1 = V9_MOTOR, pin 2 = MOTOR4_LOWContinuity.
5. Programming and Debug Interface
  • Program the Pico over its onboard USB connector.
  • Use USB serial monitor at 115200 baud.
  • ESP-01S AT interface uses Pico Serial1 on GP0/GP1 at 115200 baud.
Procedure:
  1. Flash firmware with no motors connected.
  2. Open serial monitor.
  3. Confirm startup text appears.
  4. Send raw AT command through USB serial; expect OK from ESP-01S.
6. Functional Validation

Table

TestComponentsInputExpected OutputPass Criteria
WiFi AT responseJ1, U1, U3USB command ATESP returns OKStable serial response.
Motor 1 gateJ1, R5, R9, Q1m1 128 firmware commandQ1:G PWMPWM observed, motor terminal low-side switches.
Motor 2 gateJ1, R6, R10, Q2m2 128Q2:G PWMPWM observed.
Motor 3 gateJ1, R7, R11, Q3m3 128Q3:G PWMPWM observed.
Motor 4 gateJ1, R8, R12, Q4m4 128Q4:G PWMPWM observed.
7. Motor Test Procedure
  1. Use a current-limited bench supply first, then repeat with the actual 6xAA battery pack after current is known.
  2. Connect one motor to J3 only.
  3. Start at low PWM duty cycle.
  4. Measure motor current and MOSFET temperature.
  5. Repeat for J4, J5, and J6.
  6. Test all motors together only after individual current is confirmed.
Pass/Fail Summary

Table

SectionResultNotes
Visual inspection[ ] Pass / [ ] Fail
Power rails[ ] Pass / [ ] Fail
ESP boot pins[ ] Pass / [ ] Fail
UART / AT response[ ] Pass / [ ] Fail
Motor gates[ ] Pass / [ ] Fail
Motor load test[ ] Pass / [ ] Fail
Open Safety Items
  • Add or externally provide input current limiting before testing unknown motors.
  • Do not run stalled motors without confirming MOSFET, diode, trace, and supply thermal limits.

  • 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. Motor Test Procedure

  • Pass/Fail Summary

  • Open Safety Items