How to Use ESP-01 Wi-Fi Relay Module

The ESP-01 Wi-Fi module shown in Figure 1 is a widely known member of the ESP8266 microcontroller board family. Because of its low cost and small size, it is usually used for applications where only a few GPIOs (General Purpose Input / Output) are needed. One such application is the ESP-01 Wi-Fi Relay Module shown in Figure 2.

Did you know that there are two (2) versions of ESP-01 Wi-Fi modules? Check out the article:
Difference Between ESP-01 and ESP-01S

A picture of an ESP-01 Wi-Fi module used as a microcontroller for the ESP-01 Wi-Fi relay module. — Figure 1. ESP-01 ESP8266 Wi-Fi Module

The ESP-01 Wi-Fi relay module is used as a smart switch for remotely turning on and off any device connected to it. A pre-programmed ESP-01 module is inserted into the relay module to serve as a microcontroller for the relay. The attached ESP-01 module also provides the Wi-Fi capability to the relay module to enable a computer or a smartphone to control the relay module remotely or wirelessly.

Picture of an ESP-01 Wi-Fi relay module without the ESP-01 module. — Figure 2. ESP-01 Wi-Fi Relay Module

Picture showing the ESP-01 Wi-Fi relay module with the ESP-01 module. — Figure 3. ESP-01 Wi-Fi Relay Module with ESP-01 Module

ESP-01 Module Programmer

In order to use the ESP-01 Wi-Fi relay module, a programmer is needed to program the ESP-01 module. An example of an ESP-01 programmer is shown in Figure 3. If you do not a have an ESP-01 programmer module, you can make one if you have a USB-to-serial converter. Or simply use an Arduino board as an ESP-01 programmer if you have an available Arduino board. For details on how to make a DIY ESP-01 programmer, see the article: ESP-01 and ESP-01S Pinout and Configuration

Picture of an ESP-01 programmer module for use in pre-programming an ESP-01 module to be used on ESP-01 Wi-Fi relay module. — Figure 4. ESP-01 USB-to-Serial Converter Programmer

Schematic Diagram of ESP-01 Wi-Fi Relay Module

Before we start programming the ESP-01 module to be used on the ESP-01 Wi-Fi relay module, let us first study the schematic diagram of the ESP-01 Wi-Fi relay module. There are two (2) versions of ESP-01 Wi-Fi relay modules. Version 1 is shown in Figure 5 and Version 4 is shown in Figure 6.

Schematic diagram of the ESP-01 Wi-Fi relay module version 1. — Figure 5. Schematic Diagram of ESP-01 Wi-Fi Relay Module Version 1

Schematic diagram of the newer ESP-01 Wi-Fi relay module version 4 . — Figure 6. Schematic Diagram of ESP-01 Wi-Fi Relay Module Version 4

An examination of the two (2) schematic diagrams above will show that the difference in the two versions has something to do with the relay driver. On version 1, the relay is driven by an NPN junction transistor. On the other hand, on version 4, the relay is driven by an N-channel MOSFET transistor. Also, in version 4, the MOSFET driving the relay is in turn being driven by an opto-coupler.

In terms of programming, we should note that on both versions, the relay is activated by the ESP-01 module thru port GPIO0. However, on Version 1, the relay uses ACTIVE HIGH logic levels. That is, a logic HIGH on GPIO0 will activate the relay and a logic LOW will deactivate it. On the other hand, on a Version 4 model, the relay is activated using ACTIVE LOW signals. This means that a logic HIGH will turn OFF the relay and a logic LOW will turn it ON. In short, the two versions use opposite signals for activating the relay. These differing signals should be taken into account when programming the ESP-01 module. Or else, turning ON the relay may result to it being turned OFF instead. And vice versa, turning the relay OFF may cause the relay to turn ON.

How to Program the ESP-01 Module for Use with the Wi-Fi Relay Module

In this article, we will pre-program the ESP-01 module with NodeMCU or Lua program. Afterwards, we will create a smartphone app to control the ESP-01 Wi-Fi relay module remotely. It is also possible to program the ESP-01 module with the Arduino IDE. If you would prefer an Arduino IDE program for the ESP-01 module, please see – How to Control ESP-01 Without a Router.

Flashing the NodeMCU Firmware on ESP-01 Module

First, we need to install the NodeMCU firmware into the ESP-01 module. There are several ways to do this but we will use the one that I think is the easiest. Download the NodeMCU Flasher from Github. Extract the zip file and run the file “ESP8266Flasher.exe”. There are two versions of ESP8266Flasher.exe, a Win32 and a Win64 version. Select the appropriate version for your computer.

Screenshot of NodeMCU Flasher for installing NodeMCU firmware on an ESP-01 module. — Figure 7. NodeMCU Flasher

Plug in your ESP-01 programmer with the ESP-01 module to your computer’s USB port. The NodeMCU Flasher should be able to detect the ESP-01 programmer and automatically change the COM Port setting. If this is your first time to use your ESP-01 programmer, you may have to install the device driver for it.

A picture of the NodeMCU Firmware Programmer for the ESP8266 modules like the ESP-01 module to be used for the ESP-01 Wi-Fi relay module. — Figure 8. NodeMCU Flasher Detects the Correct COM Port

Click on Config tab of the NodeMCU Flasher and verify that you have the settings INTERNAL://NODEMCU and hex 0x00000. The INTERNAL://NODEMCU setting tells the NodeMCU Flasher to use the NodeMCU firmware that comes with the NodeMCU Flasher installation (the firmware file can be found under the Resources/Binaries directory). Meanwhile, the setting 0x00000 is the memory starting location where the NodeMCU firmware will be installed. See Figure 9 for the correct settings.

A picture of the NodeMCU Flasher with the Config tab showing the correct settings. — Figure 9. NodeMCU Flasher with the Config Settings

Next, click on the Advanced tab of the NodeMCU Flasher. Change the Flash size to 1Mbyte and the SPI mode to QIO. These two (2) settings are specific to ESP-01 modules, see Figure 10 below.

NodeMCU Flasher with the Advanced settings changed for the ESP-01 Wi-Fi module — Figure 10. NodeMCU Flasher Advanced Settings

Click back on the Operation tab and click on the Flash(F) button to start flashing the NodeMCU firmware to the ESP-01 module. Please refer to Figure 11.

The NodeMCU Flasher ready to flash the NodeMCU firmware on an ESP-01 Wi-Fi module. — Figure 11. NodeMCU Flasher Prior to Flashing

Wait for the progress bar to be filled up and you should see a green checkmark at the bottom left of the NodeMCU Flasher screen as depicted in Figure 12.

Picture of the NodeMCU Flasher with the green checkmark indicating a successful firmware flashing. — Figure 12. NodeMCU Flasher with Green Checkmark

We have now successfully installed the NodeMCU firmware on the ESP-01 module, so we will go to the next procedure.

ESPlorer Integrated Development Environment

ESPlorer is an Integrated Development Environment (IDE) used for programming ESP8266 modules like ESP-01 with NodeMCU and Micropython. Download the ESPlorer from Github. Extract the zip file and run the file “ESPlorer.bat”.

Make sure that the proper COM port for your ESP-01 programmer is selected and the baud rate setting is 9600 baud (see Figure 14). Then click on the Open button.

Picture of ESPlorer IDE showing the correct setting before opening the communication port — Figure 14. ESPlorer IDE with the Correct Settings

If the ESPlorer can’t autodetect the NodeMCU firmware, reset the ESP-01 module by pressing the reset button on your ESP-01 programmer. Or click on the RTS button on the ESPlorer IDE twice. When you click the RTS button on the ESPlorer IDE, it sends a RESET signal to the connected ESP-01 programmer module.

ESPlorer IDE showing the message can't autodetect firmware. — Figure 15. ESPlorer IDE with Error Message

After resetting the ESP-01 module, you should see a message with the NodeMCU firmware version. This verifies that you have successfully flashed the ESP-01 module with the NodeMCU firmware in the preceding procedure.

If the ESPlorer IDE cannot detect your NodeMCU firmware, see the article:
ESPlorer Can’t Autodetect Firmware

ESPlorer IDE showing a successful firmware detection signifying readiness to accept scripts for programming the ESP-01 module to used for the ESP-01 Wi-Fi relay module. — Figure 16. ESPlorer IDE with the NodeMCU Firmware Detected

The Lua Program

Copy and paste the following Lua program on the left pane of the ESPlorer IDE.

print("Ready to start soft ap")

local str=wifi.ap.getmac();
local ssidTemp=string.format("%s%s%s",string.sub(str,10,11),string.sub(str,13,14),string.sub(str,16,17));

cfg={}
cfg.ssid="ESP8266_"..ssidTemp;
cfg.pwd="12345678"
wifi.ap.config(cfg)

cfg={}
cfg.ip="192.168.1.1";
cfg.netmask="255.255.255.0";
cfg.gateway="192.168.1.1";
wifi.ap.setip(cfg);
wifi.setmode(wifi.SOFTAP)

str=nil;
ssidTemp=nil;
collectgarbage();

print("Soft AP started")
print("Heep:(bytes)"..node.heap());
print("MAC:"..wifi.ap.getmac().."\r\nIP:"..wifi.ap.getip());

led1 = 3
led2 = 4
gpio.mode(led1, gpio.OUTPUT)
gpio.mode(led2, gpio.OUTPUT)
srv=net.createServer(net.TCP)
srv:listen(80,function(conn)
    conn:on("receive", function(client,request)
        local buf = "";
        buf = buf.."HTTP/1.1 200 OK\n\n"
        local _, _, method, path, vars = string.find(request, "([A-Z]+) (.+)?(.+) HTTP");
        if(method == nil)then
            _, _, method, path = string.find(request, "([A-Z]+) (.+) HTTP");
        end
        local _GET = {}
        if (vars ~= nil)then
            for k, v in string.gmatch(vars, "(%w+)=(%w+)&*") do
                _GET[k] = v
            end
        end
        
        if(_GET.pin == "ON1")then
              gpio.write(led1, gpio.HIGH);
			  print("led1 on")
        elseif(_GET.pin == "OFF1")then
              gpio.write(led1, gpio.LOW);
			print("led1 off")
        elseif(_GET.pin == "ON2")then
              gpio.write(led2, gpio.HIGH);
			print("led2 on")
        elseif(_GET.pin == "OFF2")then
              gpio.write(led2, gpio.LOW);
			print("led2 off")
        end
        client:send(buf);
        client:close();
        collectgarbage();
    end)
end)

print("Ready to start soft ap")

local str=wifi.ap.getmac();

local ssidTemp=string.format("%s%s%s",string.sub(str,10,11),string.sub(str,13,14),string.sub(str,16,17));

cfg={}

cfg.ssid="ESP8266_"..ssidTemp;

cfg.pwd="12345678"

wifi.ap.config(cfg)

cfg={}

cfg.ip="192.168.1.1";

cfg.netmask="255.255.255.0";

cfg.gateway="192.168.1.1";

wifi.ap.setip(cfg);

wifi.setmode(wifi.SOFTAP)

str=nil;

ssidTemp=nil;

collectgarbage();

print("Soft AP started")

print("Heep:(bytes)"..node.heap());

print("MAC:"..wifi.ap.getmac().."\r\nIP:"..wifi.ap.getip());

led1 = 3

led2 = 4

gpio.mode(led1, gpio.OUTPUT)

gpio.mode(led2, gpio.OUTPUT)

srv=net.createServer(net.TCP)

srv:listen(80,function(conn)

conn:on("receive", function(client,request)

local buf = "";

buf = buf.."HTTP/1.1 200 OK\n\n"

local _, _, method, path, vars = string.find(request, "([A-Z]+) (.+)?(.+) HTTP");

if(method == nil)then

_, _, method, path = string.find(request, "([A-Z]+) (.+) HTTP");

end

local _GET = {}

if (vars ~= nil)then

for k, v in string.gmatch(vars, "(%w+)=(%w+)&*") do

_GET[k] = v

end

if(_GET.pin == "ON1")then

gpio.write(led1, gpio.HIGH);

print("led1 on")

elseif(_GET.pin == "OFF1")then

gpio.write(led1, gpio.LOW);

print("led1 off")

elseif(_GET.pin == "ON2")then

gpio.write(led2, gpio.HIGH);

print("led2 on")

elseif(_GET.pin == "OFF2")then

gpio.write(led2, gpio.LOW);

print("led2 off")

end

client:send(buf);

client:close();

collectgarbage();

end)

Figure 17 is a picture of the ESPlorer Integrated Development Environment showing a Lua script. — Figure 17. ESPlorer IDE with Lua Script

Save the file to your computer. Click the Save button on the top left pane (1). Name the file as “init.lua” (2). Then click on the Save button on the Save screen (3).

ESPlorer IDE annotated with instructions for saving a Lua script. — Figure 18. ESPlorer IDE Annotated on How to Save a Script

After saving the program to your hard disk, the ESPlorer IDE uploaded the file init.lua to your ESP-01 module and ran the program (dofile(“init.lua”)).

ESPlorer IDE with the Lua script or program executed successfully. — Figure 19. ESPlorer IDE After Running Script

Testing the ESP-01 Module Access Point

Before we proceed to building the smartphone app to control the ESP-01 Wi-Fi relay module, let us first check if we have successfully programmed the ESP-01 module.

Get your smartphone and scan for Wi-Fi devices. With my Android smartphone, I would go to the “Settings/Network and Internet/Wi-Fi” setting. See Figure 20. You should see the Wi-Fi SSID “ESP8266_XXXXXX” where XXXXXX is the last six digits of your ESP-01 module’s MAC address.

Picture of a smartphone showing the nearby Wi-Fi devices. — Figure 20. Smartphone Showing Nearby Wi-Fi Devices

Connect your smartphone to the ESP-01 access point by entering the password “12345678” (Figure 21).

Screenshot of a smartphone showing how to enter the password in order to connect to the ESP-01 Wi-Fi module. — Figure 21. Smartphone with Password Entry

Figure 22 below shows the smartphone connected to the ESP-01 module’s access point.

Smartphone showing a successful connection with the ESP-01 module access point. — Figure 22. Smartphone Connected to the ESP-01 Module

Click on the gear icon to display the network details. Your smartphone will be assigned an IP address of 192.168.1.2. The gateway is the IP address of the ESP-01 access point.

Smartphone showing the network details of the connection with the ESP-01 access point. — Figure 23. Smartphone Showing Network Details

Now we are ready to create the smartphone app to control the ESP-01 Wi-Fi relay module.

How to Create the Smartphone App to Control the ESP-01 Wi-Fi Relay Module

We are going to use the MIT App Inventor 2 to create a smartphone app to control the ESP-01 Wi-Fi relay module. First, we need to download the MIT App Inventor 2 Companion App to our smartphones. We will need it to facilitate installing the created controller app to our smartphones.

Screenshot of MIT App Inventor 2 Companion App to be used for downloading the completed ESP8266 Controller smartphone app for controlling the ESP-01 Wi-Fi relay module remotely. — Figure 24. MIT App Inventor 2 Companion App

Next, download the source code from Github – ESP8266 Controller. Extract the file ESP8266_Controller.aia.

Go to MIT App Inventor website and click on the Create Apps! button.

Screenshot of the MIT App Inventor website to be used for programming the ESP-01 Wi-Fi module. — Figure 25. The MIT App Inventor Website

Import the project ESP8266_Controller.aia (the file downloaded from Github).

MIT App Inventor 2 screen showing how to import a project file. — Figure 26. MIT App Inventor Project Import

MIT App Inventor screen showing how to export the project file ESP8266_controller.aia. — Figure 27. MIT App Inventor with Import Project Screen

The ESP8266 controller app designers view.

Picture of the MIT App Inventor showing the designer screen for the ESP8266 Controller app to be use for controlling the ESP-01 Wi-Fi relay module. — Figure 28. MIT App Inventor with the Imported ESP8266 Controller Project

If you want to modify how the program works, go to the Blocks view.

Screenshot of the MIT App Inventor in Blocks mode showing the ESP8266 Controller's program blocks. — Figure 29. MIT App Inventor Showing the Blocks Screen

Compile and build the app by clicking the Build/Android App(apk) item on the menu. Refer to Figure 30 below.

MIT App Inventor screengrab showing how to build the ESP8266 Controller app for the ESP-01 Wi-Fi relay module. — Figure 30. MIT App Inventor Showing How to Start the Build Operation

After a successful build, a bar code will appear on your computer’s screen (see Figure 31). Scan the bar code with your smartphone using the MIT App Inventor Companion app. Follow the instructions on your smartphone to install the ESP8266 Controller app.

Picture of MIT App Inventor screen display showing the bar code for downloading the ESP8266 Controller smartphone app for the ESP-01 Wi-Fi relay module. — Figure 31. MIT App Inventor with the Bar Code

How to Use the ESP8266 Controller App to Control the ESP-01 Wi-Fi Relay Module

Screenshot of the completed ESP8266 Controller smartphone app ready for use with the ESP-01 Wi-Fi relay module. — Figure 32. ESP8266 Controller App

Remove the ESP-01 module from the programmer module and insert it into the ESP-01 Wi-Fi relay module. Provide power to the relay module. Next, connect the smartphone to the ESP-01 access point as discussed above on testing the ESP-01 module access point. Then, open the ESP8266 Controller app and set the IP address to “192.168.1.1”.

You may now enjoy playing around with your new smart switch ESP-01 Wi-Fi relay module using the ESP8266 Controller smartphone app.

References on How to Use ESP-01 Wi-Fi Relay Module

ESP8266 on Wikipedia
ESP-01 Wi-Fi Relay Module on Shopee