Arduino Mage Npn 12v/24v 5v Io I2c Led, a ESP32 project

This industrial I/O expansion board transforms an ESP32 into a robust 24 V control interface for factory automation, machinery, and process control applications. Built around an MCP23017 I2C GPIO expander with optocoupler-isolated inputs, MOSFET-driven outputs, and dual-voltage support (5 V logic, 12–24 V switching), the board safely bridges low-power microcontroller signals to high-power industrial loads while protecting against voltage spikes and noise.

The guide provides a complete wiring diagram, detailed parts list, and step-by-step assembly instructions covering power distribution, input conditioning, output switching stages, and I2C communication setup. Included firmware demonstrates debounced input sampling, safe output sequencing, and diagnostic LED feedback, enabling makers and technicians to deploy reliable automation logic without custom PCB design.

Wiring diagram

Gather all the parts

Qty	Component
1	External 24 V 10 A DIN-rail DC power supply 24 V DC, 10 A, external DIN-rail supply An external enclosed supply that provides the board and field devices with 24 V DC.
1	RECOM R-78E5.0-1.0 switching regulator 5 V, 1 A, SIP3 A board-mounted switching regulator that converts the 12–24 V field supply to a regulated 5 V rail.
1	MCP23017 I2C GPIO expander IC TSSOP-28 A 16-pin digital I/O chip that reads eight isolated inputs and controls eight output drivers over I2C.
8	PC817C optocoupler DIP-4, CTR grade C An isolating light-coupler that safely transfers one 12–24 V NPN sensor signal to the 3.3 V logic side.
1	74AHCT541 octal buffer TSSOP-20 An eight-channel 5 V buffer that converts the MCP23017 3.3 V output signals into strong 5 V MOSFET gate-drive signals.
8	NVRGS055N06CL 60 V N-channel MOSFET SOT-23, 60 V, 70 mΩ max at VGS=4.5 V A low-side power switch that connects one 24 V load to 0 V when its control signal is on.
8	2.2 kΩ 0.5 W input resistor 2.2 kΩ, 0.5 W, 1206 A resistor that limits 12–24 V NPN sensor current before each optocoupler LED.
8	Red 0805 input status LED Red, 0805 A red light that shows when its NPN sensor input is being pulled to 0 V.
8	SS36 Schottky flyback diode SS36, 3 A, 60 V, SMA A diode that safely absorbs the voltage spike from one 24 V relay coil or solenoid when its output turns off.
8	Red 0805 output status LED Red, 0805 A red light that shows when its low-side MOSFET output is pulling the load terminal to 0 V.
8	100 Ω MOSFET gate resistor 100 Ω, 0603 A resistor that limits each MOSFET gate charging pulse and reduces electrical noise.
8	100 kΩ MOSFET gate pull-down resistor 100 kΩ, 0603 A resistor that keeps each output MOSFET safely off while the controller starts or is unplugged.
1	Logic pull-up and decoupling passive set 2×4.7 kΩ 0603; 5×100 nF 0603; 2×10 µF 0805 The I2C pull-up resistors and local ceramic capacitors that keep the logic supply and data signals stable.
1	24 V input protection set 10 A fuse, SS54 reverse diode, SMBJ33A TVS A fuse, reverse-polarity diode and surge suppressor that protect the board from a miswired or noisy 24 V field supply.
1	Two-position 5.08 mm power terminal block 2-position, 5.08 mm pitch, ≥10 A The screw terminal where the 12–24 V field supply enters the circuit board.
1	Nine-position NPN sensor terminal block 9-position, 5.08 mm pitch The screw terminal block for eight NPN sensor signal wires and their shared 0 V return.
1	Nine-position output terminal block 9-position, 5.08 mm pitch, ≥10 A The screw terminal block for eight switched low-side load terminals and the shared protected +24 V feed.
1	Six-position 5 V GPIO terminal block 6-position, 3.5 mm pitch A screw terminal for four protected 5 V logic signals plus 5 V and ground.
1	Four-pin 3.3 V I2C header 1×4, 2.54 mm A keyed header for a low-voltage I2C device using 3.3 V logic.
8	4.7 kΩ input LED resistor 4.7 kΩ, 0.25 W, 1206 A resistor that limits current through one 24 V input status LED.
8	4.7 kΩ output LED resistor 4.7 kΩ, 0.25 W, 1206 A resistor that limits current through one 24 V output status LED.
8	10 kΩ optocoupler pull-up resistor 10 kΩ, 0603 A resistor that makes one MCP23017 input read high when its optocoupler is off.
1	PCB mechanical hardware set 2×7 XIAO female headers; 4×M3 mounting holes Four mounting holes and the XIAO socket headers used to secure and plug in the controller.
8	Resettable output fuse MF-R110, 1.10 A hold PTC, radial A protective fuse that limits fault current in one 24 V output channel.
8	100 kΩ output-command pull-down resistor 100 kΩ, 0603 A resistor that keeps one output-command input low while the controller starts.
1	MCP23017 address and reset network 3×0 Ω, 10 kΩ, 100 nF 0603 Straps that set the expander to address 0x20 and keep its reset pin high.
4	5 V GPIO direction-selection jumper 1×3, 2.54 mm header plus shunt A three-pin jumper that selects whether one translated 5 V signal is an input or an output.
1	SN74LVC1T45 5 V GPIO channel 1 translator SN74LVC1T45, SC70-6 A direction-controlled chip that safely translates the first XIAO signal between 3.3 V and 5 V.
1	SN74LVC1T45 5 V GPIO channel 2 translator SN74LVC1T45, SC70-6 A direction-controlled chip that safely translates the second XIAO signal between 3.3 V and 5 V.
1	SN74LVC1T45 5 V GPIO channel 3 translator SN74LVC1T45, SC70-6 A direction-controlled chip that safely translates the third XIAO signal between 3.3 V and 5 V.
1	SN74LVC1T45 5 V GPIO channel 4 translator SN74LVC1T45, SC70-6 A direction-controlled chip that safely translates the fourth XIAO signal between 3.3 V and 5 V.

Assemble it in 8 steps

1. 准备外部 24 V 电源

把符合当地安全规范的封闭式 24 V 直流 DIN 导轨电源安装在机箱或导轨上。它的 +24V 线接到扩展板 J1 的 +24V，0V 线接到 J1 的 0V；这两根线为现场设备和扩展板供电。

先用万用表量 J1 两端，确认极性正确且电压在 12–24 V 范围内。
交流市电只接外置、封闭且合规的 DIN 导轨电源；绝不能引入这块低压 PCB。
把 +24V 与 0V 接反会使保护器件发热或损坏。

2. 安装 XIAO 控制器

将 Seeed Studio XIAO ESP32S3 插入两排 1×7 母座，USB-C 接口朝向 PCB 外缘。确认每一排针脚都进入对应孔位，不要错位一列。

先只焊两个对角针脚，确认 USB-C 位置和板边方向正确后，再焊完其余针脚。
焊接时不要让 5 V、3.3 V 或 GPIO 针脚之间产生焊锡桥接，否则可能损坏 XIAO。

3. 装配输入区域

在 PCB 的 IN1–IN8 区域装入八颗 PC817C 光耦、每路 2.2 kΩ/0.5 W 输入电阻、4.7 kΩ LED 电阻和红色输入 LED。光耦缺口和 PCB 丝印缺口必须同向；LED 的短脚或外壳色带一侧是负端，按丝印方向安装。

每装完一路，用万用表检查该路没有把 +24V 短接到 0V。
光耦和 LED 装反会导致该输入无指示或始终不工作。
输入电阻必须使用 0.5 W、1206 或更大封装；普通小电阻可能在 24 V 现场侧过热。

4. 装配输出区域

在 OUT1–OUT8 区域依照丝印安装八颗 MOSFET、每路 100 Ω 栅极电阻、100 kΩ 下拉电阻、MF-R110 自恢复保险丝、SS36 续流二极管、红色输出 LED 及其 4.7 kΩ 电阻。SS36 带条纹的一端必须朝向 +24V 丝印，另一端朝向对应 OUTn。

先检查每个 MOSFET 的封装方向，再焊接；SOT-23 的引脚很小，建议使用细焊锡和助焊剂。
把续流二极管装反会在输出开启时直接短接 24 V，可能损坏保险丝、走线或电源。
每路负载不得超过 1 A；八路同时工作时，外置电源、端子和铜箔必须承受总电流。

5. 装配逻辑与电源区域

装入 MCP23017、74AHCT541、5 V 降压稳压器、逻辑上拉电阻、去耦电容和 24 V 保护器件。MCP23017 的 A0、A1、A2 接地，I²C 地址固定为 0x20；RESET 由上拉电阻接到 3.3 V。每颗 IC 的 100 nF 电容要紧贴其电源脚。

使用放大镜检查 TSSOP 引脚；相邻引脚间不应有焊锡连桥。
MCP23017 和 XIAO 只能使用 3.3 V 逻辑；不要把 5 V 接到 SDA、SCL 或 XIAO 的 GPIO。

6. 连接传感器与执行器

每个三线 NPN 传感器：棕线接 +24V 公共端，蓝线接 0V 公共端，黑线接 IN1–IN8 中对应的一路。每个直流负载：正端接输出端子的 +24V_COM，负端接对应 OUT1–OUT8；该输出会把负端接到 0V 来启动负载。

先只接一个小型 24 V 指示灯或继电器线圈测试 OUT1，再逐路接入其余设备。
感性负载必须使用本板对应通道的续流二极管；否则关断瞬间的尖峰可能损坏 MOSFET。
不要把 NPN 传感器的黑色输出线直接接到 +24V。

7. 选择并连接 5 V GPIO 与 I2C

J4 的 IO1–IO4 经过单通道电平转换器连接到 XIAO GPIO1–GPIO4；按每路 DIR 焊盘或跳线选择方向，输出模式把 DIR 接 3.3V，输入模式把 DIR 接 GND。J5 的四针顺序为 3V3、GND、SDA、SCL，SDA 接 GPIO5，SCL 接 GPIO6。

第一次使用 5 V GPIO 时，先选择输入模式并用万用表确认外部设备没有把电压送入错误端。
不要把超过 5 V 的信号接到 J4；也不要把 24 V 现场信号接到 J4 或 J5。

8. 第一次低风险上电

先不接执行器，仅连接 XIAO 的 USB-C 与外部 24 V。确认 5 V 稳压输出为约 5.0 V、XIAO 的 3.3 V 为约 3.3 V，并确认所有 OUT 灯在上电时熄灭。随后一次连接一个传感器和一个小负载验证 INn 动作时 OUTn 与两颗状态灯一起变化。

若某一路上电即导通，立即断开 24 V，检查该路 100 kΩ 栅极下拉、MOSFET 朝向和 74AHCT541 的 OE 接地。
进行接线或更换负载前先断开 24 V 电源；带电插拔可能产生火花并损坏端子或输出器件。

Review all connections

1. Connections between "field_psu_24v" and "ESP32"

Function	field_psu_24v	ESP32
`power`	+24V → Two-position 5.08 mm power terminal block +V	EXT
`ground`	0V → Two-position 5.08 mm power terminal block 0V	EXT

2. Connections between "tb_power" and "ESP32"

Function	tb_power	ESP32
`power`	+V → 24 V input protection set FIELD_IN	EXT
`ground`	0V	GND

3. Connections between "field_protection" and "ESP32"

Function	field_protection	ESP32
`power`	FIELD_PROTECTED → RECOM R-78E5.0-1.0 switching regulator VIN	EXT
`ground`	0V	GND

4. Connections between "pcb_reg_5v" and "ESP32"

Function	pcb_reg_5v	ESP32
`power`	VIN	VIN
`ground`	GND	GND
`power`	VOUT	5V

5. Connections between "mcp23017_ic" and "ESP32"

Function	mcp23017_ic	ESP32
`power`	VDD	3V3
`ground`	VSS	GND
`i2c`	SDA	GPIO 5
`i2c`	SCL	GPIO 6
`digital`	GPA0-GPA7 → PC817C optocoupler COLLECTOR	EXT
`digital`	GPB0-GPB7 → 74AHCT541 octal buffer A0-A7	EXT

6. Connections between "opto_pc817c" and "ESP32"

Function	opto_pc817c	ESP32
`digital`	ANODE → 2.2 kΩ 0.5 W input resistor END2	EXT
`ground`	CATHODE → Nine-position NPN sensor terminal block IN1-IN8	EXT
`digital`	COLLECTOR → MCP23017 I2C GPIO expander IC GPA0-GPA7	EXT
`ground`	EMITTER	GND

7. Connections between "input_series_resistor" and "ESP32"

Function	input_series_resistor	ESP32
`power`	END1	VIN
`digital`	END2 → PC817C optocoupler ANODE	EXT

8. Connections between "input_indicator_led" and "ESP32"

Function	input_indicator_led	ESP32
`power`	ANODE	VIN
`ground`	CATHODE → Nine-position NPN sensor terminal block IN1-IN8	EXT

9. Connections between "tb_inputs" and "ESP32"

Function	tb_inputs	ESP32
`ground`	COM_0V	GND
`digital`	IN1-IN8 → PC817C optocoupler CATHODE	EXT

10. Connections between "output_buffer" and "ESP32"

Function	output_buffer	ESP32
`power`	VCC	5V
`ground`	GND	GND
`digital`	A0-A7 → MCP23017 I2C GPIO expander IC GPB0-GPB7	EXT
`digital`	Y0-Y7 → 100 Ω MOSFET gate resistor END1	EXT
`ground`	OE1_OE2	GND

11. Connections between "gate_resistor" and "ESP32"

Function	gate_resistor	ESP32
`digital`	END1 → 74AHCT541 octal buffer Y0-Y7	EXT
`digital`	END2 → NVRGS055N06CL 60 V N-channel MOSFET GATE	EXT

12. Connections between "mosfet_gate_pulldown" and "ESP32"

Function	mosfet_gate_pulldown	ESP32
`digital`	END1 → NVRGS055N06CL 60 V N-channel MOSFET GATE	EXT
`ground`	END2	GND

13. Connections between "output_mosfet" and "ESP32"

Function	output_mosfet	ESP32
`digital`	GATE → 100 Ω MOSFET gate resistor END2	EXT
`digital`	DRAIN → Nine-position output terminal block OUT1-OUT8	EXT
`ground`	SOURCE	GND

14. Connections between "output_flyback_diode" and "ESP32"

Function	output_flyback_diode	ESP32
`ground`	ANODE → Nine-position output terminal block OUT1-OUT8	EXT
`power`	CATHODE	VIN

15. Connections between "output_indicator_led" and "ESP32"

Function	output_indicator_led	ESP32
`power`	ANODE	VIN
`digital`	CATHODE → Nine-position output terminal block OUT1-OUT8	EXT

16. Connections between "tb_outputs" and "ESP32"

Function	tb_outputs	ESP32
`power`	+24V_COM	VIN
`digital`	OUT1-OUT8 → NVRGS055N06CL 60 V N-channel MOSFET DRAIN	EXT

17. Connections between "hdr_i2c" and "ESP32"

Function	hdr_i2c	ESP32
`power`	3V3	3V3
`ground`	GND	GND
`i2c`	SDA	GPIO 5
`i2c`	SCL	GPIO 6

18. Connections between "logic_passives" and "ESP32"

Function	logic_passives	ESP32
`power`	3V3	3V3
`power`	5V	5V
`ground`	GND	GND

19. Connections between "input_led_resistor" and "ESP32"

Function	input_led_resistor	ESP32
`power`	END1	VIN
`digital`	END2 → Red 0805 input status LED ANODE	EXT

20. Connections between "output_led_resistor" and "ESP32"

Function	output_led_resistor	ESP32
`power`	END1	VIN
`digital`	END2 → Red 0805 output status LED ANODE	EXT

21. Connections between "opto_pullup_resistor" and "ESP32"

Function	opto_pullup_resistor	ESP32
`power`	END1	3V3
`digital`	END2 → MCP23017 I2C GPIO expander IC GPA0-GPA7	EXT

22. Connections between "board_hardware" and "ESP32"

Function	board_hardware	ESP32
`ground`	GND_REFERENCE	GND

23. Connections between "output_fuse" and "ESP32"

Function	output_fuse	ESP32
`power`	IN	VIN
`power`	OUT → Nine-position output terminal block +24V_COM	EXT

24. Connections between "buffer_input_pulldown" and "ESP32"

Function	buffer_input_pulldown	ESP32
`digital`	END1 → 74AHCT541 octal buffer A0-A7	EXT
`ground`	END2	GND

25. Connections between "mcp_config" and "ESP32"

Function	mcp_config	ESP32
`ground`	A0_A1_A2	GND
`power`	RESET_PULLUP	3V3
`ground`	DECOUPLING_GND	GND

26. Connections between "gpio_dir_jumper" and "ESP32"

Function	gpio_dir_jumper	ESP32
`power`	OUTPUT_SELECT	3V3
`ground`	INPUT_SELECT	GND
`digital`	COMMON → SN74LVC1T45 5 V GPIO channel 1 translator DIR	EXT

27. Connections between "gpio_translator_1" and "ESP32"

Function	gpio_translator_1	ESP32
`power`	VCCA	3V3
`power`	VCCB	5V
`ground`	GND	GND
`digital`	A	GPIO 1
`digital`	B → Six-position 5 V GPIO terminal block IO1-IO4	EXT
`digital`	DIR → 5 V GPIO direction-selection jumper COMMON	EXT

28. Connections between "gpio_translator_2" and "ESP32"

Function	gpio_translator_2	ESP32
`power`	VCCA	3V3
`power`	VCCB	5V
`ground`	GND	GND
`digital`	A	GPIO 2
`digital`	B → Six-position 5 V GPIO terminal block IO1-IO4	EXT
`digital`	DIR → 5 V GPIO direction-selection jumper COMMON	EXT

29. Connections between "gpio_translator_3" and "ESP32"

Function	gpio_translator_3	ESP32
`power`	VCCA	3V3
`power`	VCCB	5V
`ground`	GND	GND
`digital`	A	GPIO 3
`digital`	B → Six-position 5 V GPIO terminal block IO1-IO4	EXT
`digital`	DIR → 5 V GPIO direction-selection jumper COMMON	EXT

30. Connections between "gpio_translator_4" and "ESP32"

Function	gpio_translator_4	ESP32
`power`	VCCA	3V3
`power`	VCCB	5V
`ground`	GND	GND
`digital`	A	GPIO 4
`digital`	B → Six-position 5 V GPIO terminal block IO1-IO4	EXT
`digital`	DIR → 5 V GPIO direction-selection jumper COMMON	EXT

31. Connections between "tb_gpio5v" and "ESP32"

Function	tb_gpio5v	ESP32
`power`	+5V	5V
`ground`	GND	GND

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_MCP23X17.h>


// Forward declarations
void setOutputsOff();

constexpr uint8_t I2C_SDA_PIN = 5;
constexpr uint8_t I2C_SCL_PIN = 6;
constexpr uint8_t GPIO5V_1_PIN = 1;
constexpr uint8_t GPIO5V_2_PIN = 2;
constexpr uint8_t GPIO5V_3_PIN = 3;
constexpr uint8_t GPIO5V_4_PIN = 4;
constexpr uint8_t MCP_ADDRESS = 0x20;
constexpr uint8_t CHANNEL_COUNT = 8;
constexpr uint32_t INPUT_STABLE_MS = 20;

Adafruit_MCP23X17 io;
bool stableInput[CHANNEL_COUNT] = {false};
bool sampledInput[CHANNEL_COUNT] = {false};
uint32_t lastChangeMs[CHANNEL_COUNT] = {0};

void setOutputsOff() {
  for (uint8_t channel = 0; channel < CHANNEL_COUNT; ++channel) {
    io.digitalWrite(channel + 8, LOW);
  }
}

void setup() {
  Serial.begin(115200);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);

  pinMode(GPIO5V_1_PIN, INPUT);
  pinMode(GPIO5V_2_PIN, INPUT);
  pinMode(GPIO5V_3_PIN, INPUT);
  pinMode(GPIO5V_4_PIN, INPUT);

  if (!io.begin_I2C(MCP_ADDRESS, &Wire)) {
    Serial.println("MCP23017 not found at 0x20; outputs remain unavailable.");
    while (true) delay(1000);
  }

  for (uint8_t channel = 0; channel < CHANNEL_COUNT; ++channel) {
    io.pinMode(channel, INPUT_PULLUP);
    io.pinMode(channel + 8, OUTPUT);
  }
  setOutputsOff();
  Serial.println("Industrial 8-in/8-out board ready.");
}

void loop() {
  const uint32_t now = millis();
  for (uint8_t channel = 0; channel < CHANNEL_COUNT; ++channel) {
    const bool sensorOn = (io.digitalRead(channel) == LOW);
    if (sensorOn != sampledInput[channel]) {
      sampledInput[channel] = sensorOn;
      lastChangeMs[channel] = now;
    }
    if (sampledInput[channel] != stableInput[channel] &&
        now - lastChangeMs[channel] >= INPUT_STABLE_MS) {
      stableInput[channel] = sampledInput[channel];
      io.digitalWrite(channel + 8, stableInput[channel] ? HIGH : LOW);
      Serial.printf("IN%u=%s, OUT%u=%s\n", channel + 1,
                    stableInput[channel] ? "ON" : "OFF", channel + 1,
                    stableInput[channel] ? "ON" : "OFF");
    }
  }
}