• Status: Review
• ESP32 DevKitC 38-pin carrier PCB for a smart-city demonstration with distance sensing, servo actuation, sound/sensitivity analog inputs, and six building-light outputs.

• Low-voltage indoor prototype or educational demonstrator.
• Powered by a regulated external 5 V DC adapter.
• Not intended for safety-critical motion control or outdoor exposure without further protection.

• Read an HC-SR04 ultrasonic sensor.
• Drive one hobby servo from GPIO13.
• Sample an analog microphone on GPIO34.
• Sample an external sensitivity potentiometer on GPIO35.
• Independently drive six external LEDs.
• Use ESP32 Wi-Fi/Bluetooth capabilities for future connectivity.

• ESP32-DEVKITC-VE 38-pin module.
• 5 V screw-terminal input.
• HC-SR04 header with protected ECHO input.
• Servo header with local bulk capacitance and startup pulldown.
• 3.3 V microphone and potentiometer headers.
• Six active-high, resistor-limited LED headers.

Diagram

• J1 PIN1 = 5V_EXT; J1 PIN2 = GND.
• 5V_EXT feeds U1 5V, HC-SR04 VCC, and servo VCC.
• C1 470 uF + C2 100 nF support servo transients.
• C3 47 uF + C4 100 nF support the DevKit 5 V input.
• U1 3V3 supplies the microphone and external potentiometer.

• J2 pin 1 VCC, pin 2 TRIG, pin 3 ECHO, pin 4 GND.
• TRIG uses GPIO4.
• ECHO passes through R7 10 kΩ / R8 18 kΩ divider to GPIO5; 5 V becomes approximately 3.21 V.

• J3 Gnd/5v/Data pin names are used directly.
• GPIO13 drives Data through R9 470 Ω.
• R10 10 kΩ pulls the connector-side servo signal low during reset.

• Microphone J4: pin 1 3V3, pin 2 GPIO34, pin 3 GND; C5 100 nF bypass.
• Potentiometer J5: VCC 3V3, Output GPIO35, GND common.
• GPIO34 and GPIO35 are ESP32 ADC1 input-only pins and remain usable while Wi-Fi is active.

• Header P1 is the resistor-limited active-high signal; P2 is GND.
• R11 10 kΩ holds GPIO12 low at reset to protect the flash-voltage boot strap.

• J1: regulated 5 V DC input.
• J2: HC-SR04.
• J3: hobby servo.
• J4: 3.3 V analog microphone module; output must remain within 0–3.3 V.
• J5: recommended 10 kΩ linear potentiometer.
• J6–J11: external LEDs only; external voltage must not be driven into these outputs.

• Continuous operation from a wall adapter; no battery subsystem.
• Use a 5 V, 2 A minimum adapter for a known micro-servo; 5 V, 3 A preferred when stall current is unknown.
• Do not power the DevKit simultaneously from USB and J1 unless the exact board revision is confirmed to prevent backfeed.

• See the Power Budget project file.
• 5V_EXT and GND are tagged for 2 A nominal and 3 A peak design current.

• Through-hole external connectors and radial bulk capacitors; 0603 resistors and bypass capacitors.
• C1 and C3 are polarized electrolytics: P1 to 5V_EXT, P2 to GND.
• During PCB layout, use at least 0.5 mm / 20 mil for 5 V and GND, preferably wider for the servo branch and return.
• Route servo current directly between J1 and J3; avoid sharing the microphone/potentiometer ground path.

• Arduino-compatible ESP32 firmware.
• GPIO12 must initialize low before enabling LED channel 1.
• Servo GPIO13 should remain low/detached until commanded.
• ADC attenuation should be configured for GPIO34/GPIO35.

• Place the DevKit antenna at the board edge with no copper or components under/around its antenna region.
• Keep J1 and J3 close together to minimize the high-current loop.
• Keep analog connectors and traces away from the servo power path.

• Added HC-SR04 ECHO divider because ESP32 GPIO is not 5 V tolerant.
• Added servo bulk/bypass capacitance and startup pulldown.
• Retained all user-requested GPIO assignments.
• Did not add reverse-polarity protection or a fuse to preserve the requested direct 5 V architecture; these remain recommended options.

• External supply is regulated 5 V.
• HC-SR04 module has conventional 5 V ECHO behavior.
• External LEDs are connected anode to header signal and cathode to header GND.
• Servo accepts a 3.3 V PWM high level.

• Initial schematic created with safety corrections and documentation.