MicroPython: Relay Module with ESP32/ESP8266 (Guide + Web Server)

Using a relay with the ESP32 or ESP8266 is a great way to control AC household appliances remotely. This tutorial explains how to control a relay module with the ESP32 or ESP8266 using MicroPython firmware.

MicroPython Relay Module with ESP32 and ESP8266: Guide and Web Server

We’ll take a look at how a relay module works, how to connect the relay to the ESP32 or ESP8266 boards and build a web server to control a relay remotely.

We have similar guides using Arduino IDE:

Prerequisites

To follow this tutorial you need MicroPython firmware installed in your ESP32 or ESP8266 boards. You also need an IDE to write and upload the code to your board. We suggest using Thonny IDE or uPyCraft IDE:

Learn more about MicroPython: MicroPython Programming with ESP32 and ESP8266 eBook.

Introducing Relays

A relay is an electrically operated switch and like any other switch, it that can be turned on or off, letting the current go through or not. It can be controlled with low voltages, like the 3.3V provided by the ESP32/ESP8266 GPIOs and allows us to control high voltages like 12V, 24V or mains voltage (230V in Europe and 120V in the US).

1, 2, 4, 8, 16 Channels Relay Modules

There are different relay modules with a different number of channels. You can find relay modules with one, two, four, eight and even sixteen channels. The number of channels determines the number of outputs we’ll be able to control.

Relay modules with different number of channels 1, 2, 4, 8, 16 Channels

There are relay modules whose electromagnet can be powered by 5V and with 3.3V. Both can be used with the ESP32 or ESP8266 – you can either use the VIN pin (that provides 5V) or the 3.3V pin.

Additionally, some come with built-in optocoupler that add an extra “layer” of protection, optically isolating the ESP boards from the relay circuit.

Get a relay module:

Relay Pinout

For demonstration purposes, let’s take a look at the pinout of a 2-channel relay module. Using a relay module with a different number of channels is similar.

2-channel Relay Module Pinout

On the left side, there are two sets of three sockets to connect high voltages, and the pins on the right side (low-voltage) connect to the ESP GPIOs.

Mains Voltage Connections

Relay module mains voltage side

The relay module shown in the previous photo has two connectors, each with three sockets: common (COM), Normally Closed (NC), and Normally Open (NO).

  • COM: connect the current you want to control (mains voltage).
  • NC (Normally Closed): the normally closed configuration is used when you want the relay to be closed by default. The NC are COM pins are connected, meaning the current is flowing unless you send a signal from the ESP to the relay module to open the circuit and stop the current flow.
  • NO (Normally Open): the normally open configuration works the other way around: there is no connection between the NO and COM pins, so the circuit is broken unless you send a signal from the ESP to close the circuit.

Control Pins

2-channel Relay Module

The low-voltage side has a set of four pins and a set of three pins. The first set consists of VCC and GND to power up the module, and input 1 (IN1) and input 2 (IN2) to control the bottom and top relays, respectively.

If your relay module only has one channel, you’ll have just one IN pin. If you have four channels, you’ll have four IN pins, and so on.

The signal you send to the IN pins, determines whether the relay is active or not. The relay is triggered when the input goes below about 2V. This means that you’ll have the following scenarios:

  • Normally Closed configuration (NC):
    • HIGH signal – current is flowing
    • LOW signal – current is not flowing
  • Normally Open configuration (NO):
    • HIGH signal – current is not flowing
    • LOW signal – current in flowing

You should use a normally closed configuration when the current should be flowing most of the times, and you only want to stop it occasionally.

Use a normally open configuration when you want the current to flow occasionally (for example, turn on a lamp occasionally).

Power Supply Selection

2-channel relay module control pins

The second set of pins consists of GND, VCC, and JD-VCC pins. The JD-VCC pin powers the electromagnet of the relay. Notice that the module has a jumper cap connecting the VCC and JD-VCC pins; the one shown here is yellow, but yours may be a different color.

With the jumper cap on, the VCC and JD-VCC pins are connected. That means the relay electromagnet is directly powered from the ESP power pin, so the relay module and the ESP circuits are not physically isolated from each other.

Without the jumper cap, you need to provide an independent power source to power up the relay’s electromagnet through the JD-VCC pin. That configuration physically isolates the relays from the ESP with the module’s built-in optocoupler, which prevents damage to the ESP in case of electrical spikes.

Wiring a Relay Module to the ESP32/ESP8266

Warning: in this example, we’re dealing with mains voltage. Misuse can result in serious injuries. If you’re not familiar with mains voltage ask someone who is to help you out. While programming the ESP or wiring your circuit make sure everything is disconnected from mains voltage.

Alternatively, you can use a 12V power source to control 12V appliances.

ESP32 Schematic Diagram

Connect the relay module to the ESP32 as shown in the following diagram. The diagram shows wiring for a 2-channel relay module, wiring a different number of channels is similar.

Wiring a Relay Module to the ESP32 Schematic Circuit

In this example, we’re controlling a lamp. We just want to light up the lamp occasionally, so it is better to use a normally open configuration.

We’re connecting the IN1 pin to GPIO 26, you can use any other suitable GPIO. See ESP32 GPIO Reference Guide.

ESP8266 Schematic Diagram

Follow the next schematic diagram if you’re using an ESP8266.

Wiring a Relay Module to the ESP8266 Schematic Circuit

We’re connecting the IN1 pin to GPIO 5, you can use any other suitable GPIO. See ESP8266 GPIO Reference Guide.

The best ESP8266 pins to use with relays are: GPIO 5, GPIO 4, GPIO 14, GPIO 12 and GPIO 13.

Controlling a Relay Module – MicroPython Code (Script)

The code to control a relay with the ESP32 or ESP8266 is as simple as controlling an LED or any other output. In this example, as we’re using a normally open configuration, we need to send a LOW signal to let the current flow, and a HIGH signal to stop the current flow.

Control a Lamp with the ESP32 or ESP8266 using a Relay Module

Copy the following code to the main.py file and upload it to your board. It lights up your lamp for 10 seconds and turn it off for another 10 seconds.

# Complete project details at https://RandomNerdTutorials.com

from machine import Pin
from time import sleep

# ESP32 GPIO 26
relay = Pin(26, Pin.OUT)

# ESP8266 GPIO 5
#relay = Pin(5, Pin.OUT)

while True:
  # RELAY ON
  relay.value(0)
  sleep(10)
  # RELAY OFF
  relay.value(1)
  sleep(10)

View raw code

How the code works

Import the Pin class from the machine module to interact with the GPIOs. We also import the sleep() method from the time module to add delays.

from machine import Pin
from time import sleep

Then, we define a Pin object called relay on 26 (if you’re using an ESP32) and define it as an output.

# ESP32 GPIO 26
relay = Pin(26, Pin.OUT)

In case you’re using an ESP8266, use GPIO 5 instead. Comment the previous line and uncomment the following.

# ESP8266 GPIO 5
#relay = Pin(5, Pin.OUT)

In the while loop, send a LOW signal to light up the lamp for 10 seconds.

# RELAY ON
relay.value(0)
sleep(10)

If you’re using a normally closed configuration, send a HIGH signal to light up the lamp.

Stop the current flow by sending a HIGH signal to the relay pin. If you’re using a normally closed configuration, send a LOW signal to stop the current flow.

# RELAY OFF
relay.value(1)
sleep(10)

Control Relay Module with MicroPython Web Server

Control Relay with Web Server - MicroPython ESP32 and ESP8266

In this section, we’ve created a web server example that allows you to control a relay remotely via web server.

boot.py

Copy the following code to your boot.py file.

# Complete project details at https://RandomNerdTutorials.com

try:
  import usocket as socket
except:
  import socket

from machine import Pin
import network

import esp
esp.osdebug(None)

import gc
gc.collect()

ssid = 'REPLACE_WITH_YOUR_SSID'
password = 'REPLACE_WITH_YOUR_PASSWORD'

station = network.WLAN(network.STA_IF)

station.active(True)
station.connect(ssid, password)

while station.isconnected() == False:
  pass

print('Connection successful')
print(station.ifconfig())

# ESP32 GPIO 26
relay = Pin(26, Pin.OUT)

# ESP8266 GPIO 5
#relay = Pin(5, Pin.OUT)

View raw code

Insert your network credentials in the following variables:

ssid = 'REPLACE_WITH_YOUR_SSID'
password = 'REPLACE_WITH_YOUR_PASSWORD'

Uncomment one of the following lines accordingly to the board you’re using. By default, it’s set to use the ESP32 GPIO.

# ESP32 GPIO 26
relay = Pin(26, Pin.OUT)

# ESP8266 GPIO 5
#relay = Pin(5, Pin.OUT)

main.py

Copy the following to your main.py file.

# Complete project details at https://RandomNerdTutorials.com

def web_page():
  if relay.value() == 1:
    relay_state = ''
  else:
    relay_state = 'checked'
  html = """<html><head><meta name="viewport" content="width=device-width, initial-scale=1"><style>
  body{font-family:Arial; text-align: center; margin: 0px auto; padding-top:30px;}
  .switch{position:relative;display:inline-block;width:120px;height:68px}.switch input{display:none}
  .slider{position:absolute;top:0;left:0;right:0;bottom:0;background-color:#ccc;border-radius:34px}
  .slider:before{position:absolute;content:"";height:52px;width:52px;left:8px;bottom:8px;background-color:#fff;-webkit-transition:.4s;transition:.4s;border-radius:68px}
  input:checked+.slider{background-color:#2196F3}
  input:checked+.slider:before{-webkit-transform:translateX(52px);-ms-transform:translateX(52px);transform:translateX(52px)}
  </style><script>function toggleCheckbox(element) { var xhr = new XMLHttpRequest(); if(element.checked){ xhr.open("GET", "/?relay=on", true); }
  else { xhr.open("GET", "/?relay=off", true); } xhr.send(); }</script></head><body>
  <h1>ESP Relay Web Server</h1><label class="switch"><input type="checkbox" onchange="toggleCheckbox(this)" %s><span class="slider">
  </span></label></body></html>""" % (relay_state)
  return html

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('', 80))
s.listen(5)

while True:
  try:
    if gc.mem_free() < 102000:
      gc.collect()
    conn, addr = s.accept()
    conn.settimeout(3.0)
    print('Got a connection from %s' % str(addr))
    request = conn.recv(1024)
    conn.settimeout(None)
    request = str(request)
    print('Content = %s' % request)
    relay_on = request.find('/?relay=on')
    relay_off = request.find('/?relay=off')
    if relay_on == 6:
      print('RELAY ON')
      relay.value(0)
    if relay_off == 6:
      print('RELAY OFF')
      relay.value(1)
    response = web_page()
    conn.send('HTTP/1.1 200 OK\n')
    conn.send('Content-Type: text/html\n')
    conn.send('Connection: close\n\n')
    conn.sendall(response)
    conn.close()
  except OSError as e:
    conn.close()
    print('Connection closed')

View raw code

We won’t explain how this code works because we already have a very similar tutorial with detailed explanation of each line of code. Read the next project:

Demonstration

After making the necessary changes, upload the boot.py and main.py files to your board. Press the EN/RST button and in the Shell you should get the ESP IP address.

ESP32 ESP8266 Relay Web Server IP Address

Then, open a browser in your local network and type the ESP IP address to get access to the web server.

You should get a web page with a toggle button that allows you to control your relay remotely using your smartphone or your computer.

Control a relay with web server using ESP32 or ESP8266 using MicroPython firmware

Enclosure for Safety

For a final project, make sure you place your relay module and ESP inside an enclosure to avoid any AC pins exposed.

Plastic Enclosure for Safety and hide exposed AC pins of the relay module

Wrapping Up

In this tutorial you’ve learned how to control relays with the ESP32 or ESP8266 using MicroPython. We have similar guides using Arduino IDE:

Controlling a relay with the ESP32 or ESP8266 is as easy controlling any other output, you just need to send HIGH and LOW signals as you would do to control an LED.

You can use our web server examples that control outputs to control relays. You just need to pay attention to the configuration you’re using. In case you’re using a normally open configuration, the relay works with inverted logic. You can use the following web server examples to control your relay:

Learn more about MicroPython with the ESP32 and ESP8266 with our resources:

Thanks for reading.


Learn how to program and build projects with the ESP32 and ESP8266 using MicroPython firmware DOWNLOAD »

Learn how to program and build projects with the ESP32 and ESP8266 using MicroPython firmware DOWNLOAD »


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2 thoughts on “MicroPython: Relay Module with ESP32/ESP8266 (Guide + Web Server)”

  1. I am planning a similar system but with 8 relays. I have an 8 relay card physically interfaced to an ESP32, via Port ‘A’ on a MCP23017 I/O Expander. I would like to use Port ‘B’ of the MCP23017 for local control of the relays. Suggestions on how best to mod the code here to accommodate my setup? Thanks.

    Reply
  2. Hi, I made a similar project with ESP-01 and 1-channel relay. The relay is connected to GPIO0, have boot.py and main.py programs. It works ok when I connect the relay after the ESP was booted. But by finished and connected device, every time after connecting to the power network, the relay is high, and main.py was avoided.
    It is probably hardware problem, does it help if I put resistor or capacitor to GPIO0? Or is ESP8266 bad choice for such a device?

    Reply

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