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Build a Low-Voltage Smart Power Strip Simulator

Build a low-voltage ESP32 smart power strip simulator with MOSFET outputs on GPIO25, GPIO26, GPIO27, GPIO33 and no mains wiring.

IntermediateAges 12+60-75 minUnder 30 USDParent Safe
Project Mission

Build a Low-Voltage Smart Power Strip Simulator

The Story

A smart power strip sounds like a mains project, but this safe Golden version teaches the control pattern without touching dangerous wiring. You build a low-voltage simulator that behaves like four controllable outlets while switching only DC demo loads.

Explain Like I'm 12

Each GPIO pin tells a MOSFET gate to allow or block current through one small DC load. The ESP32 web page flips those gates, and the code starts with everything OFF so a reset does not surprise you.

Learning Support

  • Recommended ageAges 12+
  • Adult supervisionRequired to confirm the build remains low-voltage DC only.
  • Classroom useUse battery or bench-supply DC loads; do not bring mains wiring into the activity.
  • Parent promptAsk why the simulator uses MOSFETs and low-voltage loads instead of a modified power strip.
  • Screen-free activitySketch four independent DC channels with a shared ground and a master-off button.
  • Next challengeAdd current sensing on the low-voltage side after the four base channels are stable.
  • Skills practiced
    • MOSFET low-side switching
    • Fail-safe startup
    • Local web controls
    • Shared-ground wiring
  • Learning outcomes
    • Switch four low-voltage DC loads with GPIO25, GPIO26, GPIO27, and GPIO33.
    • Start every channel OFF before Wi-Fi or the web page begins.
    • Use a master-off route.
    • Explain why mains power strips are out of scope.
  • Mini experiments
    • Toggle one channel at a time.
    • Reset the ESP32 and confirm all channels start OFF.
    • Add a flyback diode before testing any coil load.

Safety Standards

  • Unplug USB before changing jumper wires. Recheck 3.3 V, 5 V, and GND before reconnecting power.
  • Do not power motors, pumps, LED strips, or servos from the ESP32 3.3 V pin. Use a suitable external supply and common ground.
  • Breadboards are for low-current prototypes. Move high-current or unattended builds to proper terminals, enclosure, strain relief, and fusing.
  • Relay and mains-voltage projects require isolation, correct relay ratings, enclosed wiring, and qualified adult supervision.

What You Will Build

A web-controlled four-channel low-voltage DC switching simulator with fail-safe OFF startup and a master-off control.

Components List

  • ESP32 DevKit boardLow-voltage control board for the web interface.
  • Four logic-level N-channel MOSFETsSwitch low-voltage DC loads from GPIO25/GPIO26/GPIO27/GPIO33.
  • Four low-voltage DC loadsLED strips, small lamps, or other safe DC demo loads within their rated supply.
  • Separate low-voltage load supplyMatches the demo loads; share ground with the ESP32.
  • Flyback diodes for inductive loadsRequired across motors, relays, solenoids, or coils.

Bill of Materials

PartQtyEstimated CostNotes
ESP32 DevKit board1VariesLow-voltage control board for the web interface.
Four logic-level N-channel MOSFETs1VariesSwitch low-voltage DC loads from GPIO25/GPIO26/GPIO27/GPIO33.
Four low-voltage DC loads1VariesLED strips, small lamps, or other safe DC demo loads within their rated supply.
Separate low-voltage load supply1VariesMatches the demo loads; share ground with the ESP32.
Flyback diodes for inductive loads1VariesRequired across motors, relays, solenoids, or coils.

Wiring

Use GPIO25/GPIO26/GPIO27/GPIO33 as active-HIGH MOSFET gate signals. The ESP32 ground and low-voltage load-supply ground must be common.

Wiring Diagram ESP32 GPIO25, GPIO26, GPIO27, and GPIO33 connected through logic-level MOSFET gates to four low-voltage DC loads with shared ground and flyback diodes for inductive loads.
  1. 1

    Unplug USB and the low-voltage load supply before wiring.

  2. 2

    Connect ESP32 GND to the load-supply GND.

  3. 3

    Connect GPIO25, GPIO26, GPIO27, and GPIO33 to the four MOSFET gates through suitable gate resistors.

  4. 4

    Wire each low-voltage load through its MOSFET on the DC side only.

  5. 5

    Add a flyback diode across every inductive load before applying power.

  6. 6

    Power the ESP32, upload the sketch, and confirm all channels are OFF before opening the web page.

GPIO Mapping

SignalESP32 PinDirectionNotes
Channel 1 MOSFET gateGPIO25OutputActive HIGH low-voltage control.
Channel 2 MOSFET gateGPIO26OutputActive HIGH low-voltage control.
Channel 3 MOSFET gateGPIO27OutputActive HIGH low-voltage control.
Channel 4 MOSFET gateGPIO33OutputActive HIGH low-voltage control.

Circuit Explanation

Each MOSFET acts as a low-side switch for one DC load. The ESP32 drives only the gate signal; the load current comes from the separate low-voltage supply.

Engineering Explanation

The selected GPIOs avoid common ESP32 boot-strap pins used in the previous staged relay design. The sketch drives all outputs LOW before Wi-Fi starts and includes a master-off route for a fail-safe default.

Libraries

  • Arduino ESP32 WiFi and WebServerBuilt into the Arduino ESP32 core.

Code

Copy into Arduino IDE. Install any libraries noted in the component guides first.

esp32-low-voltage-power-strip-simulator.ino 
// ESP32 low-voltage smart power strip simulator
// Switch only low-voltage DC loads. Do not connect this circuit to mains power.
#include <WiFi.h>
#include <WebServer.h>

const char* WIFI_SSID = "YOUR_WIFI_NAME";
const char* WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";

const int CHANNEL_PINS[4] = {25, 26, 27, 33};
bool channelOn[4] = {false, false, false, false};

WebServer server(80);

void applyOutputs() {
  for (int i = 0; i < 4; i++) {
    digitalWrite(CHANNEL_PINS[i], channelOn[i] ? HIGH : LOW);
  }
}

void allOff() {
  for (int i = 0; i < 4; i++) channelOn[i] = false;
  applyOutputs();
}

void servePanel() {
  String html = "<!doctype html><html><body><h1>Low-Voltage Smart Power Strip Simulator</h1>";
  html += "<p>DC demo loads only - no mains wiring.</p><p><a href='/alloff'>Master OFF</a></p>";
  for (int i = 0; i < 4; i++) {
    html += "<p>Channel " + String(i + 1) + ": ";
    html += channelOn[i] ? "ON" : "OFF";
    html += " <a href='/toggle?ch=" + String(i) + "'>Toggle</a></p>";
  }
  html += "</body></html>";
  server.send(200, "text/html", html);
}

void handleToggle() {
  int ch = server.arg("ch").toInt();
  if (ch >= 0 && ch < 4) {
    channelOn[ch] = !channelOn[ch];
    applyOutputs();
  }
  server.sendHeader("Location", "/");
  server.send(302, "text/plain", "");
}

void handleAllOff() {
  allOff();
  server.sendHeader("Location", "/");
  server.send(302, "text/plain", "");
}

void setup() {
  Serial.begin(115200);

  for (int i = 0; i < 4; i++) {
    pinMode(CHANNEL_PINS[i], OUTPUT);
    digitalWrite(CHANNEL_PINS[i], LOW);
  }
  allOff();

  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  server.on("/", servePanel);
  server.on("/toggle", handleToggle);
  server.on("/alloff", handleAllOff);
  server.begin();

  Serial.print("Open local control page: http://");
  Serial.println(WiFi.localIP());
}

void loop() {
  server.handleClient();
}

Code Explanation

The sketch configures GPIO25/GPIO26/GPIO27/GPIO33 as outputs, immediately turns every channel OFF, then starts a local web panel with per-channel toggles and a master-off route.

Expected Output

After reset all channels are OFF. Serial Monitor prints the local web address; the page shows four low-voltage channels and a Master OFF link. No channel turns on until a user toggles it.

Troubleshooting

  • A channel turns on during reset Confirm the sketch uses GPIO25/GPIO26/GPIO27/GPIO33 and that all outputs are driven LOW before Wi-Fi starts.
  • Load does not switch Check the shared ground, MOSFET orientation, gate wiring, and load supply voltage.
  • ESP32 resets when a load switches Separate the load supply from USB power, add flyback diodes for coils, and keep load current out of the ESP32 board.

Common Mistakes

  • Connecting the project to mains wiring.
  • Using relay modules and boot pins from the old staged version.
  • Forgetting the shared ground between ESP32 and the DC load supply.
  • Testing a motor or solenoid without a flyback diode.

Testing Checklist

  • Power with no loads first.
  • Confirm all channels start OFF.
  • Test one DC load at a time.
  • Use flyback diodes before coil testing.

Engineering Tips

  • Keep mains out of the enclosure.
  • Use logic-level MOSFETs.
  • Name channels by load voltage, not household socket labels.

Upgrade Ideas

  • Add per-channel low-voltage current sensing.
  • Add MQTT control for the same DC simulator.
  • Add saved schedules that still default OFF after firmware upload.

Real-World Applications

  • Low-voltage automation trainer
  • Classroom web-control demo
  • MOSFET switching practice

FAQs

Can I modify a real power strip?

No. This tutorial is only a low-voltage DC simulator.

Why use MOSFETs instead of relays?

MOSFETs keep the project focused on safe DC switching and avoid mains relay claims.

Review, Testing, and References

Author: Abdul Mubeen and the ESP32 Engine editorial team. Last updated: 2026-07-10. Reviewed: wiring logic, Arduino code structure, beginner safety, and learning sequence.

Educational level: Intermediate. Estimated completion time: 60-75 min. This project is for learning and prototyping; production or unattended hardware needs additional engineering review.

Project Complete!

You built a safer smart-strip learning model: four low-voltage DC channels, safe GPIO choices, fail-safe OFF startup, and a master-off route. The project teaches automation control without touching mains wiring.

  • Low-voltage MOSFET switching
  • Fail-safe output initialization
  • Local web control
  • Inductive-load protection