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

Design Notes and Power Budget — Remote Pico Controller
Selected Architecture
  • Controller: Raspberry Pi Pico seated on J1.
  • WiFi: ESP-01S (U1) using UART to Pico GP0/GP1.
  • Motor drive: Four independent low-side N-MOSFET switches (Q1–Q4) driven by GP18–GP21.
  • Input: External 6xAA battery pack represented by BT1 (4xAA) plus BT2 (2xAA) wired in series and connected through J2.
  • Regulation: 9V -> 5V buck (U2), then 5V -> 3.3V LDO (U3) for ESP-01S.
Datasheet-Grounded Component Notes

Table

ComponentKey Datasheet Point Used
ESP-01S (U1)3.0V–3.6V supply, current >300mA recommended, UART interface, default 115200 baud.
LMR50410Y5 (U2)Fixed 5V / 1A buck; FB tied to output for fixed output; EN must not float; 100nF bootstrap from CB to SW; typical 5V application uses 4.7uH and 10uF output.
AP2112K-3.3 (U3)2.5V–6.0V VIN, 600mA output, 1uF input and output capacitors recommended.
IRLZ44NPBF (Q1–Q4)TO-220 N-MOSFET, 55V VDS, logic-level family; RDS(on) specified at 4V/5V/10V, so 3.3V gate drive should be validated thermally.
1N5822RLG (D1–D4)3A / 40V Schottky diode used as each motor flyback diode.
Power Budget
Logic Rail Estimate

Table

LoadRailTypical / Peak EstimateNotes
Raspberry Pi PicoV5 -> Pico VSYS50–150mA typical assumedDepends on firmware and attached USB/debug activity.
ESP-01SV3V3_WIFI~71mA average TX, ~300mA peakDatasheet current >300mA supply recommendation.
Pull-ups / passivesV3V3_WIFIV9_MOTOR.
  • Motor negative terminal -> MOSFET drain / flyback diode anode.
  • MOSFET source -> GND.
  • Flyback diode cathode -> V9_MOTOR.
Supported behavior:
  • On/off switching.
  • PWM speed control.
Not supported:
  • Reverse direction.
  • Active braking.
  • Closed-loop current control.
  • Stall detection.
Independent Review Findings Incorporated
An independent design review confirmed the basic topology is workable for a simple low-side motor switch board. One change was incorporated immediately: motor gate pulldowns were reduced from 100kΩ to 47kΩ for stronger off-state noise immunity.
  • Confirm motor current, stall current, and AA cell chemistry/current capability.
  • Add input fuse or polyfuse if users may attach arbitrary motors.
  • Add reverse-polarity protection and a TVS clamp on V9_MOTOR if supply misuse or motor transients are expected.
  • Consider larger input bulk capacitance if motors start simultaneously.
  • Consider series resistors on UART lines if Pico USB power may be present while 9V input is absent.
  • Consider MOSFETs with RDS(on) specified at 2.5V/3.0V, or add gate drivers, if PWM current is high.
  • Add test points for V9_MOTOR, V5, V3V3_WIFI, GND, and motor gate nets.

  • Selected Architecture

  • Datasheet-Grounded Component Notes

  • Power Budget

  • Logic Rail Estimate

  • Motor Rail Estimate

  • Motor Channel Behavior

  • Independent Review Findings Incorporated

  • Recommended Before Layout