ESP32 LED PCB Design

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A robust beginner-friendly onboard topology for each 24 V high-side channel is:
ESP32 GPIO → optocoupler or NPN level shifter → P-channel MOSFET high-side switch → LED color wire receives +24 V when active
This is simple, through-hole friendly, active-high from GPIO, and much more robust than trying to drive 24 V directly from the NodeMCU or using small signal transistors as the load switch.
First: challenge the assumptions
Before committing, verify these points:
  1. Do the LED “color wires” really need +24 V?
    Many 12/24 V RGB LED strips are common-anode: the common wire is +24 V and the R/G/B wires are switched to ground with low-side N-MOSFETs.
    If that is your LED type, you do not want high-side switching. You want three low-side N-MOSFETs.
  2. If the load wires truly need +24 V when active, then high-side switching is correct.
    That implies the LED/load common return is tied to 0 V/GND.
  3. Do not power the NodeMCU directly from 24 V.
    Use a 24 V-to-5 V buck converter feeding the NodeMCU 5 V/VIN pin, or a proper 3.3 V regulator. Most NodeMCU boards cannot tolerate 24 V on VIN.
  4. The external MT-301R4P-N module must be verified.
    Make sure it actually provides a 24 V sourcing/high-side output. Some opto modules provide sinking/open-collector outputs instead.
  5. If isolation matters, do not accidentally defeat it.
    If the external opto module is meant to isolate the ESP32 from the 24 V side, tying ESP32 GND to 24 V return elsewhere removes that isolation.
Recommended onboard channel circuit
Use this per channel for GPIO25, GPIO26, GPIO27.
Functional block 
Text
ESP32 GPIO
   |
   |  logic input resistor
   v
Optocoupler or NPN pull-down stage
   |
   v
P-channel MOSFET gate drive
   |
   v
P-channel MOSFET high-side switch
   |
   v
LED color output receives +24 V when active
Preferred onboard robust version: optocoupled P-MOSFET high-side switch
This keeps the ESP32 side better protected and matches the spirit of the external opto-module fallback.
Per-channel schematic concept 
Text
ESP32 side:

GPIO25/26/27 ---- RIN ---->| optocoupler LED ---- ESP32 GND
                    390R to 680R


24 V power side:

Protected +24 V rail
        |
        |
       Source
      QP1 P-channel MOSFET
       Drain -------------------- LED_COLOR_OUT
        |
       load to 0 V/GND externally


P-MOSFET gate network:

+24 V ---- RGS ---- Gate
          47k

Gate ---- DZ ---- +24 V
       12 V zener
       anode at gate,
       cathode at +24 V/source

Gate ---- RG ---- optocoupler transistor collector
       4.7k

optocoupler transistor emitter ---- 24 V return/GND
When the ESP32 GPIO goes high, the optocoupler turns on, pulls the P-MOSFET gate down, the P-MOSFET turns on, and the LED color wire receives +24 V.
Exact suggested values per channel

Table

ItemSuggested value / partNotes
High-side MOSFETFQP27P06, IRF4905, or similar P-channel TO-220 MOSFETUse ≥55/60 V VDS rating. Size current rating to LED load.
Gate pull-up resistor, RGS47 kΩ, 0.25 WKeeps MOSFET off by default.
Gate pull-down series resistor, RG4.7 kΩ, 0.25 WLimits zener/opto current.
Gate-source zener, DZ12 V zener, e.g. BZX55C12 or 1N5242BProtects MOSFET VGS from exceeding max rating.
OptocouplerDIP phototransistor optocoupler, preferably VCEO ≥ 50 VTLP785, VO617A, or similar. Avoid marginal parts if 24 V bus is noisy.
GPIO input resistor, RIN390 Ω to 680 ΩGives roughly 3–5 mA opto LED current from 3.3 V GPIO.
Optional GPIO pulldown100 kΩ from GPIO side input to GNDEnsures off during reset/boot if desired.
Optional output indicatorLED + 10 kΩ, 0.25 W from output to GNDShows channel active.
Optional output bleed100 kΩ from output to GNDPrevents floating output when off.
Why the 12 V zener is important
A P-channel MOSFET source sits at +24 V. If you simply pull its gate to 0 V, then:
Text
VGS = 0 V - 24 V = -24 V
Many MOSFETs have an absolute maximum VGS of only ±20 V. That is not safe.
The 12 V zener clamps the gate so that when on:
Text
VGS ≈ -12 V
That fully enhances most power P-MOSFETs while protecting the gate oxide.
Simpler non-isolated onboard version
If you do not need isolation and the ESP32 ground is already tied to the 24 V return, replace the optocoupler output transistor with a through-hole NPN transistor.
Per-channel non-isolated version 
Text
ESP32 GPIO ---- 4.7k ---- base of 2N5551 / PN2222
                         |
                       100k
                         |
                        GND

NPN emitter ---- GND

NPN collector ---- 4.7k ---- P-MOSFET gate

P-MOSFET source ---- protected +24 V
P-MOSFET drain  ---- LED_COLOR_OUT

47k from P-MOSFET gate to source/+24 V

12 V zener from gate to source:
    zener cathode to +24 V/source
    zener anode to gate
Recommended NPN: 2N5551 is nice because it has higher voltage margin than a basic 2N3904. PN2222/2N2222 can work, but their 40 V rating gives less transient margin.
Example channel behavior
Assuming the optocoupled or NPN version:

Table

GPIO stateGate stateP-MOSFETOutput
GPIO low / resetGate pulled to +24 VOffFloating/off
GPIO highGate pulled about 12 V below sourceOnLED color wire gets +24 V
So the channel is active-high, which is intuitive for ESP32 firmware.
Power/input safeguards for the whole board
For a beginner-friendly 24 V board, I would add these before the three high-side channels:
1. Input fuse or resettable PTC
Place near the 24 V input connector.
Example:
Text
24 V_IN ---- fuse/PTC ---- protected +24 V rail
Select based on total LED current.
Examples:
  • 500 mA if the load is small indicators.
  • 1 A to 2 A for moderate LED loads.
  • Higher only if traces, connectors, MOSFETs, and supply are sized accordingly.
2. Reverse-polarity protection
Use either:
  • A series Schottky diode, simple but wastes power, or
  • A P-channel MOSFET reverse-polarity protector, better for higher current.
For a beginner board, a series diode may be acceptable at low current. For LED strips, use MOSFET reverse protection.
3. 24 V transient suppressor
Add a TVS diode across the protected 24 V rail:
Text
protected +24 V ---- TVS ---- GND
Suggested:
  • SMBJ33A or SMBJ36A, depending on expected supply tolerance.
Use a unidirectional TVS for DC supply protection.
4. Bulk capacitance
Near the MOSFETs and output connectors:
  • 100 µF to 470 µF, 35 V or 50 V electrolytic
  • 100 nF ceramic in parallel
Use 50 V caps if the 24 V supply is industrial/noisy.
Output safeguards per channel
For each LED color output:
  1. Per-channel fuse/PTC if wiring leaves the board
    Especially useful for beginner wiring mistakes.
  2. Optional output TVS or clamp for long cables
    If LED wires are long, add ESD/transient protection from output to GND.
  3. Flyback diode only if the load may be inductive
    For LEDs it is not required.
    If someone may connect a relay/solenoid, add a diode from GND to output:
Text
diode anode  ---- GND
diode cathode ---- switched output
  1. Use adequately rated screw terminals
    Do not use tiny headers for amp-level 24 V LED currents.
Jumper fallback arrangement
Do not let the onboard driver and external module fight each other. Use a selector jumper per channel.
Output selection jumper
For each color channel, use a 3-pin jumper:
Text
          [ONBOARD_OUT]
                |
                o
                |
LED_COLOR_OUT --o  center pin
                |
                o
                |
          [EXT_MODULE_OUT]
Jumper position chooses:
  • Center to ONBOARD_OUT: onboard P-MOSFET drives the LED wire.
  • Center to EXT_MODULE_OUT: external MT-301R4P-N module drives the LED wire.
This prevents both drivers from being connected to the same LED wire at once.
GPIO/input selection jumper
Also consider a second selector for each GPIO:
Text
GPIO25 ---- center jumper pin
              |
      -----------------
      |               |
 onboard input     external module input
This lets each GPIO drive either:
  • The onboard opto/NPN gate driver, or
  • The external module input.
If you do not add this, at least place series resistors so the GPIO cannot be back-driven by the external module.
Suggested connector/header layout
For the external MT-301R4P-N fallback, provide a header like:
Text
EXT MODULE HEADER

1  +24 V protected
2  24 V return/GND
3  GPIO25 signal, through 330R/1k
4  GPIO26 signal, through 330R/1k
5  GPIO27 signal, through 330R/1k
6  EXT_OUT_25
7  EXT_OUT_26
8  EXT_OUT_27
Then route EXT_OUT_25/26/27 to the output selection jumpers.
Label polarity and active level clearly on silkscreen.
MOSFET choice notes
For beginner through-hole use, TO-220 P-channel MOSFETs are convenient.
Good examples:
  • FQP27P06: 60 V, through-hole, good general choice.
  • IRF4905: 55 V, very low RDS(on), good for higher currents.
  • IRF9540N: common, but higher RDS(on); okay for smaller loads.
For 24 V systems, I would prefer 60 V or higher VDS. A 30 V MOSFET is too close to the bus voltage.
Recommended per-channel circuit summary
Use this as the onboard channel:
Text
GPIO25/26/27
    |
   390R-680R
    |
opto LED
    |
ESP32 GND


24 V side:

+24V_PROTECTED ---- source of P-MOSFET
P-MOSFET drain ---- ONBOARD_OUT_x

47k from gate to source
12 V zener from gate to source:
    cathode to source/+24 V
    anode to gate

4.7k from gate to optocoupler collector
opto emitter to 24 V return/GND
Then:
Text
ONBOARD_OUT_x ---- jumper option A
EXT_MODULE_OUT_x - jumper option B
LED_COLOR_x ------ jumper center
Final recommendation
For each of GPIO25, GPIO26, and GPIO27, use a P-channel MOSFET high-side switch with a 12 V gate-source zener clamp and an optocoupler or NPN pull-down gate driver. Make the onboard circuit active-high, off by default, and isolate it from the external module with proper selector jumpers.
If you want maximum beginner robustness, I would use:
  • FQP27P06 P-channel MOSFET per channel
  • TLP785 / VO617A-class DIP optocoupler per channel
  • 47 kΩ gate-source pull-up
  • 4.7 kΩ gate pull-down series resistor
  • 12 V zener from gate to source
  • 390 Ω to 680 Ω GPIO-to-opto LED resistor
  • Input fuse/PTC
  • SMBJ33A/SMBJ36A TVS
  • 100–470 µF bulk capacitor
  • 3-pin output selector jumper per channel
  • Optional GPIO/input selector jumper per channel
This gives you a safe, through-hole, understandable, field-tolerant high-side 24 V driver while preserving the external opto-module fallback path.

flux

The initial schematic blocks are in: ESP32 socket, daisy-chain 24 V/I2C terminals, buck-module header, optional I2C pull-ups, external isolator fallback header, and onboard opto/MOSFET high-side driver channels.

flux

I created the project spec and started the schematic for the jumper-fallback ESP32 24 V LED controller. The schematic now includes the ESP32 38-pin socket, 24 V/I2C in/out terminal blocks, buck-module header, optional I2C pull-up jumpers, external MT-301R4P-N fallback header, and three onboard opto + P-channel MOSFET high-side output channels; the latest check returned no open ERC warnings/errors.
Project file: Project Specification
Open items:
  • I’m blocked from making more edits right now because the account has no available ACUs.
  • I still need to update the spec with the final schematic details and cleanly mark my last verification todo complete.
  • We still need your LED current rating and eventual enclosure dimensions before PCB layout.
Optional I2C pull-up jumper explanation: I2C needs SDA/SCL pull-up resistors, but in a daisy chain you usually only want one set enabled. JP7 enables/disables the SDA pull-up and JP8 enables/disables the SCL pull-up; install the shunts on only one board/master location, and remove them on the other slave boards.
Update spec later
Set LED current
Add jumper notes
Check BOM cost
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Schematic

Layout

3D View

Project Specification: ESP32 24V LED Controller
Project Overview
  • 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.
Intended Use
  • 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.
What the Device Should Do
  • 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.
Main Features
  • 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.
System Architecture
Diagram



  
    
  
  
    
  




















Input terminal: node_24V GND SDA SCL
Pass-through bus
Output terminal: node_24V GND SDA SCL
24V to node_5V buck module
38-pin NodeMCU ESP-32S socket
3x output select jumpers
External MT-301R4P-N header
Onboard opto/high-side drivers
LED terminal: +24V red yellow green
Hardware Subsystems
Power
  • 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.
ESP32 Carrier Socket
  • 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
I2C Daisy Chain
  • 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 Output Drivers
  • 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.
Interfaces and Connections

Table

InterfacePins / SignalsNotes
24 V/I2C input terminal24V_IN, GND, SDA, SCLFrom master/upstream box
24 V/I2C output terminal24V_OUT, GND, SDA, SCLTo downstream box
ESP32 socket38-pin NodeMCU ESP-32SThrough-hole female headers
Regulator moduleVIN+, VIN-, VOUT+, VOUT-Solder-in buck module preferred
External isolator header3.3V, GND, IN1-IN4, 24V-side terminals as neededSupports known-working MT-301R4P-N fallback
LED terminal+24V/black, red, yellow, greenColor wires need +24 V when active
Power and Runtime Expectations
  • 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.
Power Tree and Power Budget
Diagram



  
    
  
  
    
  
















24V input
24V LED power/common and color drivers
24V to node_5V buck module
5V rail
NodeMCU VIN/5V
NodeMCU onboard 3.3V
I2C pull-ups if enabled
External/onboard opto input LEDs
Initial sizing assumptions until exact LED and regulator details are known:
  • 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.
Manufacturing and Assembly Expectations
  • 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.
Firmware-Relevant Hardware Requirements
  • 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.
Physical Design Expectations
  • 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.
Important Design Decisions
  • 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.
Assumptions
  • 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.
Change Notes
  • Initial specification created from user requirements.
  • Added jumper fallback architecture for each color output.
  • Added optional I2C pull-up jumper requirement.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Power

  • ESP32 Carrier Socket

  • I2C Daisy Chain

  • LED Output Drivers

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes