• 12V-24V DC power input through a screw terminal
• Reverse-polarity and input filtering protection
• 12V-24V to 5V buck conversion
• ESP32 development board interface powered from the 5V rail
• Relay coil drive using an on-board transistor stage
• Flyback protection across the relay coil
• Dedicated dry-contact output terminal using only COM and NO
• Optional debug connector only if it adds capability beyond the ESP32 onboard USB

• Using relay NC in the output path
• Driving external voltage onto the relay contact output
• Adding separate USB interface circuitry on the PCB

• Power input: J1 12V-24V DC machine supply
• 5V buck stage: converts input power to regulated 5V for logic and relay coil
• Controller: ESP32-WROOM-32 based 38-pin development board mounted on PCB headers
• Dry contact output: RELAY_OUT routed only to K1 COM and NO

Diagram

• The board shall accept 12V-24V DC from the machine and generate a stable 5V rail.
• The board shall power an ESP32-WROOM-32 based 38-pin development board from the 5V rail while still allowing native USB use on the dev board.
• The board shall allow an ESP32 GPIO to drive the relay transistor stage.
• The board shall expose only relay COM and NO on the dry-contact output terminal.
• The board shall leave relay NC unused.
• The board shall emulate a momentary mechanical push-button closure for the machine coin-trigger input.

• Input power: 12V-24V DC on J1
• Key rails: VIN, 5V, and GND on PCB side only
• Relay coil supply: 5V rail
• Coil protection: flyback diode across K1 coil
• Isolation requirement: RELAY_OUT must not connect to VIN, GND, or any powered PCB rail

• Through-hole relay, power terminal, dry-contact terminal, and 38-pin ESP32 header interface used for simple assembly and robust field wiring

• Keep the relay coil driver topology conventional: NPN low-side switch with flyback diode
• Use an ESP32-WROOM-32 based 38-pin development board with onboard USB instead of a bare ESP32 module
• Avoid back-power conflicts between the PCB 5V rail and the ESP32 dev board USB input
• RELAY_OUT must be a true dry contact using only COM and NO
• No PCB rail may be routed onto the relay contact side

• External machine provides 12V-24V DC input power
• External coin pulse input expects a passive contact closure on RELAY_OUT

• ESP32 dev board pinout must match the chosen 38-pin DevKitC footprint in the library
• USB back-power behavior depends on the chosen dev board implementation and must be handled conservatively

• J1 accepts 12V-24V input and the buck stage generates 5V
• ESP32 dev board receives 5V and GND correctly from the PCB
• K1 coil is driven from PCB 5V through Q1 and protected by D1
• RELAY_OUT connects only to K1 COM and K1 NO
• K1 NC is not connected
• No PCB supply rail is present on RELAY_OUT

• Inspect schematic nets for dry-contact isolation
• Review 5V power distribution and ESP32 header mapping
• Run ERC and DRC checks before prototype release

• Schematic
• BOM
• Design notes in project documentation

• RELAY_OUT is intentionally isolated and must remain free of applied PCB voltage
• ESP32 onboard USB is the preferred programming and debug interface unless a non-redundant auxiliary header is later justified

• Existing relay driver retained as a starting point for refinement
• Project scope expanded to full golf ball dispenser controller with power conversion and ESP32 dev board support
• Controller interface updated from 30-pin ESP32-DEVKIT-V1 to 38-pin ESP32-DEVKITC / ESP32-WROOM-32 based board
• Relay control remapped to IO23 on the 38-pin controller interface
• 90 x 70 mm layout checked for fit with the new controller footprint and onboard USB edge access
• U2 replacement re-validated against the photographed 38-pin ESP32 board family, preserving EXT_5V, 3V3, GND, IO23, IO21, and IO22 connections

• USB connector at the bottom
• Critical preserved functional mapping used by this project:
  • GPIO23 -> relay control
  • GPIO22 -> INA219 SCL
  • GPIO21 -> INA219 SDA
  • 3V3 -> INA219 supply and I2C pull-ups
  • 5V -> dev-board external power input
  • GND -> common logic and power reference

• Select final buck implementation for prototype versus module strategy if desired
• Decide whether any auxiliary debug header adds value beyond the dev board USB connection