4-Channel ESP32 Relay Board: Wire It Right (Active-LOW, JD-VCC and COM/NO/NC)
The Compoden 4-channel relay board for the ESP32 30-pin form factor looks simple: drop it on, pick four GPIOs, switch four loads. Most first-time failures come from three things people skip: the active-LOW inputs, the JD-VCC jumper, and which screw terminal is which.
No firmware in this guide. It's the hardware side only, so whatever sketch you already have (or whatever Soldr writes later) has a board that will actually click.
How the board is put together
Each channel is a 5V relay with an optocoupler on the input. The ESP32 only lights the LED inside the optocoupler, so the coil and the switched load stay off the GPIO.
The inputs are active LOW: GPIO LOW turns the relay on, HIGH turns it off. The coils want 5V. Don't run them from the ESP32's 3V3 pin.
What you need
- 4 Channel Relay Board for ESP32 30-Pin
- ESP32 30-Pin Board
- 5V 2A Adapter (for the relay coils)
- Jumper Wire Combo
- A 5–12V DC load for the first test (fan, LED strip or small pump)
- A matching DC supply for that load
- A multimeter and a small screwdriver
Step 1: Power the coils the right way
The board has VCC for the logic/optocoupler side and JD-VCC for the coils. Many boards ship with a jumper linking the two so one 5V supply feeds both.
For a quiet desk test, leave the jumper on and feed 5V into VCC from a separate adapter, or from the ESP32's 5V/VIN if USB can spare it. Each coil draws about 70–80mA, so four relays at once is roughly 300mA of coil current alone.
If the ESP32 resets when a relay clicks, remove the jumper and power JD-VCC from its own 5V supply. Keep GND common with the ESP32 so the coil kick stays off the 3.3V rail.
Step 2: Wire the control side
ESP32 GND to relay GND. VCC to 5V, never 3V3. IN1–IN4 to spare GPIOs — GPIO 16, 17, 18 and 19 are good picks on a 30-pin DevKit. Avoid boot pins 0, 2, 12, 15 and the flash pins 6–11.
If you're stacking the board on the headers, check the silk against your DevKit. Pinouts vary; jumper wires are safer when you're not sure.
Step 3: COM, NO and NC
Each channel has three screw terminals. COM is common. NO (normally open) connects to COM only when the relay is on. NC (normally closed) connects to COM when the relay is off.
For a load that should stay off until your sketch turns it on, put the supply through COM and NO. Leave NC empty.
Step 4: Wire a DC load and smoke-test
Start with a 5–12V DC fan, LED strip or small pump. Do not start with mains AC.
Example for a 12V fan: supply positive to the fan positive, fan negative to NO, COM to supply negative. The relay breaks one side of the circuit.
Power up with every IN pin HIGH. No relay should click. Briefly short one IN to GND — that channel's LED lights and you hear the click. Only then connect the load and toggle from your sketch.
The full wiring
| From | To |
|---|---|
| ESP32 GND | Relay board GND |
| 5V adapter + (or ESP32 5V/VIN) | Relay board VCC |
| JD-VCC jumper | On for shared 5V; off + separate 5V on JD-VCC if the ESP32 resets |
| ESP32 GPIO 16 / 17 / 18 / 19 | IN1 / IN2 / IN3 / IN4 |
| 12V supply + | Load + |
| Load - | Relay NO |
| Relay COM | 12V supply - |
| Relay NC | Leave open for a normally-off load |
A few notes so it works the first time:
- Active LOW. GPIO LOW = relay on. If your sketch writes HIGH for on, flip it.
- 5V for coils, 3.3V for IN. VCC/JD-VCC are 5V. The IN pins are happy with ESP32 3.3V through the optocoupler.
- COM–NO for normally off. That's the usual pattern. NC is for fail-safe 'on until commanded off'.
- DC first. Mains AC needs a proper enclosure, fuse and strain relief. Not a breadboard experiment.
If something's off
- Never clicks: try grounding IN by hand, confirm VCC is 5V, confirm GND is shared.
- Clicks, then the ESP32 resets: remove the JD-VCC jumper and give the coils their own 5V supply.
- Clicks, load stays dead: you're on NC instead of NO, or the supply isn't going through COM.
- LED on, no click: JD-VCC isn't powered, or try another channel.
Taking it further with Soldr
Want the firmware and a full parts plan, not just the wiring? Describe the build at soldr.ai, like "an ESP32 that switches four 12V pumps on a schedule with this 4-channel relay board". Soldr designs the hardware from the idea: it picks parts from the Compoden catalog, assigns the pins, and gives you the wiring and the firmware. Soldr is Compoden's AI, so every part in the plan is one you can order here.
Get the grounds right, respect active-LOW, start on COM–NO with a DC load, and the board will click the first time your sketch asks it to.