• Status: Draft
• Device: Through-hole-friendly carrier PCB for a 38-pin NodeMCU ESP-32S development board.
• Purpose: Convert the working prototype into one easier-to-wire PCB for controlling a 24 V industrial LED/light using I2C commands.

• Installed inside daisy-chained slave boxes.
• A master controller sends commands over I2C.
• Each slave box receives 24 V, GND, SDA, and SCL, passes them onward, and controls one 24 V LED with red/yellow/green channels.
• Prototype/learning build first; later enclosure constraints will guide layout.

• Accept 24 V DC and GND from an incoming terminal block.
• Pass 24 V, GND, SDA, and SCL to an outgoing terminal block.
• Power a plug-in 38-pin NodeMCU ESP-32S board from the 24 V input through a regulator.
• Connect ESP32 GPIO21 to I2C SDA and GPIO22 to I2C SCL.
• Use GPIO25, GPIO26, and GPIO27 as red/yellow/green control outputs.
• Drive 24 V LED color wires where each active color wire receives +24 V.
• Provide jumper-selectable fallback so each color output can use either an external MT-301R4P-N isolator module or an onboard opto/high-side driver circuit.

• 38-pin ESP32 dev-board socket using through-hole female headers.
• 24 V/I2C input and output terminal blocks.
• Through-hole/solder-in 24 V to 5 V buck regulator module footprint.
• Optional I2C pull-up resistors enabled/disabled by jumpers.
• Three selectable output paths: external isolator module input or onboard opto driver.
• LED output terminal block for black/+24 V, red, yellow, and green.
• Through-hole components preferred wherever practical.

Diagram

• 24 V input powers the system and LED.
• 24 V is converted to 5 V for the NodeMCU ESP-32S VIN/5V pin.
• The ESP32 dev board's onboard regulator generates 3.3 V logic power.
• 3.3 V may also feed the external isolator module's input side.

• Board target: NodeMCU ESP-32S v1.1, 38-pin development board.
• Required connected pins:
  • VIN/5V from regulator output
  • GND
  • GPIO21 SDA
  • GPIO22 SCL
  • GPIO25 red command
  • GPIO26 yellow command
  • GPIO27 green command
  • 3V3 available for I2C pull-ups and external isolator input-side supply if the dev board exposes it

• Incoming SDA/SCL are tied to outgoing SDA/SCL and ESP32 GPIO21/GPIO22.
• Optional pull-ups to 3.3 V are included but disabled/enabled by jumpers.
• Only one location on the whole I2C bus should normally enable pull-ups.

• LED behavior confirmed by user: black/common power wire needs +24 V; each color wire turns on when that color wire also receives +24 V.
• Therefore outputs must be 24 V high-side/source-style outputs, not low-side ground switches.
• Rev-1 schematic includes both paths:
  1. External MT-301R4P-N isolator/level-converter module path.
  2. Onboard opto/high-side driver circuit path.
• A jumper per channel selects which path receives the ESP32 GPIO signal.

• Input source: nominal 24 V DC.
• Runtime: continuous when powered.
• No battery charging or low-power sleep requirement currently specified.
• ESP32 WiFi/BLE use not currently required; I2C is the command interface.

Diagram

• ESP32 dev board peak current: design regulator for at least 500 mA available at 5 V.
• Opto input channels: estimate 5–10 mA each when active.
• LED 24 V current: TBD from LED product; terminal blocks and output drivers must be sized after the LED current is known.
• Recommended buck module target: 24 V input capable, 5 V output, at least 1 A output for margin.

• User prefers through-hole soldering.
• Use through-hole terminal blocks, headers, jumpers, DIP optocouplers, axial resistors, and radial/disc capacitors where practical.
• Solder-in buck converter module preferred over a tiny SMD switching regulator for rev 1.
• PCB layout will wait for enclosure and mechanical constraints.

• ESP32 I2C pins:
  • GPIO21 = SDA
  • GPIO22 = SCL
• ESP32 output pins:
  • GPIO25 = red
  • GPIO26 = yellow
  • GPIO27 = green
• Firmware should allow OFF, red, yellow, green, and mixed/intermediate colors by controlling the three outputs.
• I2C addressing strategy is TBD.

• Board should accept a 38-pin NodeMCU ESP-32S dev board.
• Terminal blocks should be accessible at board edges.
• Enclosure dimensions and mounting details are TBD and will be added later.
• Keep the ESP32 antenna area clear during layout if the dev board antenna remains onboard.

• Use a plug-in NodeMCU ESP-32S dev board instead of a bare ESP32 module for rev 1.
• Feed the dev board from 5 V/VIN rather than directly into 3.3 V.
• Add jumper fallback for output-driver experimentation.
• Include optional, jumper-enabled I2C pull-ups so pull-up strength can be controlled across the daisy chain.
• Prefer through-hole assembly for learning/debugging.

• The NodeMCU ESP-32S board exposes usable VIN/5V, GND, 3V3, GPIO21, GPIO22, GPIO25, GPIO26, and GPIO27 pins on its 38-pin headers.
• The LED color wires require +24 V to activate.
• The external isolator module is an MT-301R4P-N family 3.3 V-to-24 V 4-channel optocoupler/PLC converter.
• The I2C daisy-chain cable length is short enough for I2C to be acceptable for a prototype. If the cable length grows, RS-485 or CAN should be considered.

• Initial specification created from user requirements.
• Added jumper fallback architecture for each color output.
• Added optional I2C pull-up jumper requirement.