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Feature by Tim Blythman WiFi Relay Modules Connecting a microcontroller to a WiFi network is something we almost take for granted today, but 10 years ago, it was more expensive and difficult. This article examines two relay modules based on an ESP-01 module that can be controlled remotely over WiFi. T he Espressif Systems ESP8266 is a 32-bit microcontroller incorporating a WiFi radio. Initially, it came with firmware that included a TCP/IP stack. It could be controlled via a serial interface that allowed commands to be sent similarly to an old Hayes-­compatible phone-line modem. The ESP-01 is a minimalist standalone ESP8266 module that we reviewed in April 2018 (siliconchip. au/Article/11042). We also used the ESP-01 to create the Clayton’s GPS Time Source (April 2018; siliconchip. au/Article/11039). Its relatively simple circuit is shown in Fig.1. It wasn’t long before it became possible to program the various ESP8266 modules directly. The possibility of doing this with the Arduino IDE, and later the Python language in the form of MicroPython, meant that working with WiFi suddenly became very easy. Indeed, the ESP8266 is one of the main reasons the Arduino IDE has been updated to support so many different processor architectures and board types. The two WiFi relay modules covered in this article are based on the ESP8266 processor and both contain a removable ESP-01 module. That means both are programmable with the Arduino IDE, among other methods. They both come loaded with functional firmware, which means that they can be used without having to be programmed. We’ll look at their design and operation, then describe how they can be controlled. We’ll also look at the benefits of reprogramming them. Why WiFi? There are numerous possible applications for a WiFi relay, especially for things like home automation, as WiFi networks can easily cover the average home (or be expanded to do so). While the relays on both modules are rated for switching mains, you should not use them to switch mains directly. That’s because the modules are so compact that it’s impossible to ensure safe separation of the mains Fig.1: the ESP-01 module circuit is pretty simple, with the ESP8266 IC being connected to an antenna, crystal, serial flash memory chip (IC2), power LED, plus 8-pin connector CON1 for power and communications. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.2: the Z6427 has about the minimum circuitry needed for an ESP-01 module to control a relay. Several pullup resistors set the correct operating mode for the microcontroller, and a power LED and a reset button are provided. A high-side PNP transistor drives the relay. The module has no onboard voltage regulator and requires a 3.3V supply. and low-voltage parts of the circuit. You could easily use them to trigger a safer external mains relay, though. On the other hand, out-of-the-box, they are ideal for controlling things like low-voltage (eg, 12V LED) lighting, DC motors and other decorative applications. The Altronics Z6427 The Altronics Z6427 is a compact module measuring 36 × 24 × 16mm. It has a 4-pin right-angle header overhanging one end and a three-way screw terminal at the opposite end. The ESP-01 module sits over the relay and is attached to the module using a 2×4 pin socket. It’s very neatly laid out and there are mounting holes in each corner. Fig.2 shows the schematic diagram of the module. As you can see, there is not much to it. The header has connections for 3.3V power, ground and serial UART lines. These four pins connect directly to their corresponding pins on the ESP01 module. A red LED indicates when 3.3V power is applied, while the tactile switch can be used to reset the microcontroller on the ESP-01 module. Some of the ESP-01’s pins are pulled up to 3.3V by either 1kW or 4.7kW resistors. One of the ESP-01’s I/O pins, GPIO0, drives a high-side PNP transistor. When GPIO0 is driven low, the transistor conducts and powers the relay coil. A diode is provided to quench the coil voltage generated when the transistor switches off. The relay has 3A-rated contacts. The module was designed by Keyestudio, and more information about siliconchip.com.au the module can be found at (including a link to download a binary image of the firmware and software tools): siliconchip.au/link/abpv Firmware The firmware tries to connect to an access point named “KeyesWifi_S” (with the password “KeyesWifi”) if such an access point is present. If that doesn’t work, after a short while, the firmware on the Z6427 sets up a WiFi access point called “KeyesWifi_A”, with the same password. In either case, the firmware opens TCP port 8080 for incoming connections. The relay contacts will close if the string “PIN00=0” is received on that port. If “PIN00=1” is received, the relay contacts will open. This corresponds to the inverted logic that the circuit presents. The GPIO0 pin (Pin 5) that is used to drive the relay is also used to set the boot mode of the processor; that is probably the reason for the somewhat unusual PNP transistor drive circuit. This pin is also driven low as the processor boots, causing the relay to close briefly. Such behaviour may not be desired in your application! The Keyestudio web page also provides a “NetAssist” Windows PC program that can be used to test the module's operation. We have also written some Arduino sketches that can be used to test and control the relays, The Altronics Z6427 WiFi Relay Module is compact, with mounting holes being a handy touch. The detachable ESP-01 module sits over the 3A sugarcube-sized relay. 3.3V power and ground can be connected at one end, with the relay contacts available at the other end. which will be described shortly. Since the header on the Z6427 also carries serial data lines, we hooked up a serial-USB adaptor to see if anything was being sent. Fig.3 shows how you can connect this module to a CP2102 USB-serial module. There is diagnostic data at the unusual rate of 74,880 baud, which can be seen in Screen 1. The Jaycar XC3804 The Jaycar WiFi Relay is a bit larger at 45 × 28mm and has a more complex circuit; in fact, there is another microcontroller on the main module, aside from the ESP8266 on the attached ESP01 module. Fig.4 shows its schematic. There are three external connections equivalent to those on the Altronics unit. A threeway screw terminal presents the relay contacts, while a four-way pin header provides serial data and power, in this case, 5V. Another two-way screw terminal parallels the 5V and ground connections, which may be preferred for some applications. The XC3804 also hosts an AMS1117 3.3V regulator to power the 3.3V ESP-01 module. The Jaycar unit uses a low-side NPN transistor to drive the coil of a 5V relay. There is also a quenching diode. An indicator LED and its ballast resistor are in parallel with the coil, so the LED illuminates when the coil is powered. This relay has 10A contacts. Fig.3: connecting the Z6427 to a CP2102 USBserial converter module allows the diagnostic boot data to be viewed at the unusual baud rate of 74,880. Australia's electronics magazine January 2024  45 ◀ Screen 1: the Z6427’s data includes information about the access point it creates, as well as its progress in connecting to other access points. Screen 2: the XC3804 produces data about the access point and URL you need to connect to. The accented characters are actually binary commands to the STC15F104W chip that are also echoed to the external serial lines. Interestingly, the transistor is controlled by an 8-pin STC15F104W microcontroller. This micro is powered from the 5V rail and is also connected to the serial UART lines of the ESP-01 and the four-way header. There are unofficial reports that the ESP8266 processor has 5V-tolerant inputs, allowing the direct connection of the nominally 3.3V ESP8266 to a 5V microcontroller. The ENABLE pin of the ESP-01 is pulled up to 3.3V, and our module had several unpopulated component footprints too. The data sheet for this module includes the Arduino source code (siliconchip.au/link/abpw). The code is straightforward and contains elements from Arduino example sketches. The XC3804 creates an open access point named “Duinotech WiFi Relay” and also sets up a DNS responder for the “relay.net” hostname. This means that the Relay can be accessed via this host name as well as its IP address. There is also a web (HTTP) server hosting a page that provides a pair of links to control the relay remotely. The links point to the URLs relay.net/open and relay.net/close According to both the source code and the behaviour we saw, the “open” command sets the transistor’s base high, energising the relay, while “close” de-energises the relay. That is opposite to what we expected. Otherwise, the XC3804 worked as expected and was perhaps slightly easier to operate due to its inbuilt HTTP server rather than a raw TCP server. Despite the extra microcontroller, the relay on the XC3804 occasionally chattered when powered on but less often than the Z6427. Also, the relay status LED (as fitted to the XC3804) is more useful than the power LED on the Z6427; the ESP-01 module already has a tiny red LED that lights up when it is powered. This module can be wired up to a CP2102 USB-serial module, as shown in Fig.5. There is little diagnostic data available from the XC3804, apart from an instructional boot message at 9600 baud, shown in Screen 2. Further binary data (the line of accented characters) is sent whenever the URLs are requested. This data appears to be the commands to the STC15F104W for it to drive the relay. Demonstration software We have written software demonstrating how to control these modules over WiFi. Naturally, we needed a WiFi-capable microcontroller, and we have chosen to use the Pico W as it can be programmed with either the Arduino IDE or with BASIC using the WebMite firmware. Since the Pico W’s UF2 firmware files are easy to upload, we have also provided those as downloads, so you can try out our examples without even having the Arduino IDE installed. You will just need a serial terminal program, such as TeraTerm on Windows or Minicom on Linux. For the Arduino IDE, we’ve used the arduino-pico board profile version 3.1.0 from siliconchip.au/link/abpx Some of the Arduino sketches have also been tested to work with the D1 Mini ESP8266-based boards. Fig.4: the XC3804 includes an AMS1117 voltage regulator, so it will work with a 5V DC supply. It has a second microcontroller in addition to the ESP8266 on the ESP-01 module, which receives commands over a serial pair and activates the relay via a standard low-side NPN transistor arrangement. 46 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 3: our basic Z6427_CLIENT demo software for the Z6427 connects to its access point and can control the relay by sending appropriate data over the WiFi network. There are three Arduino sketches for the Z6427 and one BASIC program. There is also an Arduino sketch for the XC3804. There are some limitations to the WebMite WiFi interface that mean there are some things we cannot do with it. For each example, you can load the UF2 file by pressing the white BOOTSEL button on the Pico W while connecting it to a computer. After that, copy the appropriate UF2 file to the RPI-RP2 drive that appears and connect to the virtual USB-serial port with your terminal program. You could also compile the sketches with the Arduino IDE. Note that Arduino and the WebMite firmware use different implementations of the virtual USB-serial port, so the port name or number might differ (for the same Pico W) depending on which firmware is loaded. Z6427 remote control There are three versions of the Arduino demo software for the Z6427. One version (Z6427_CLIENT) behaves as a The XC3804 has screw terminals for power and relay contacts, plus a separate header for power and serial communications. It is larger than the Altronics unit and does not have mounting holes but the onboard relay is rated for 10A. siliconchip.com.au Screen 4: this second version of the client software can scan and connect to different Z6427 Relays. It can be pretty slow, as switching between the access points each Relay provides takes some time. WiFi station and tries to connect to the access point on a Z6427. When it does, it prints its IP address. The Relay can be controlled by typing “0” or “1” into the serial terminal; Screen 3 shows the typical output. Sometimes the connection does not work immediately, so you may need to wait up to a minute for the station to connect to the access point. It also appears that the Z6427 does not always start its access point (“KeyesWifi_A”) until it has decided that it can’t connect to any other access points (“KeyesWifi_S”). The Z6427_CLIENT_V2 sketch (or UF2 file) is designed to allow control of more than one Z6427. This sketch scans for networks with the “KeyesWifi_A” name and allocates them a letter code (A, B, C etc). Screen 4 shows its output. Entering the letter code will connect to the appropriate Relay, after which “0” and “1” will switch the specific Relay, like the previous sketch. Note that this sketch is very slow to switch between Relay access points, so it will Fig.5: the XC3804 communicates at 9600 baud, and you can see some brief debugging data output and the commands to the STC15F104W that drives the relay. Australia's electronics magazine not be suitable for practical uses of those Relays. The Z6427_AP_CLIENT demo operates as an access point and allows Relays to connect to it; its serial output is shown in Screen 5. The “0” and “1” commands are pushed out to all Relays that connect. Unfortunately, there isn’t an easy way to tell the relays apart (eg, by querying their MAC addresses) from within the Arduino code. Like the previous sketch, this version is impractical for anything but demonstration purposes, but might be handy to show how the Relays operate in these configurations. WebMite BASIC The current version of WebMite BASIC (5.07.07 at the time of writing) has some limitations that mean it is not possible to provide as many examples. Screen 5: the Z6427_AP_CLIENT sketch provides an access point to which the Z6427 Relays can connect. It shows the connected stations and sends out the same command to all the Relays it detects. January 2024  47 In particular, the WebMite cannot be configured to work with an open WiFi network, meaning that it is impossible to use it to communicate with the Jaycar XC3804, which only offers an open WiFi access point. The WebMite cannot be an access point, so we cannot create an equivalent to the Z6427_AP_CLIENT sketch. Also, the access point to which the WebMite connects is fixed as an OPTION, so it cannot be easily changed at runtime; that rules out a BASIC program like the Z6427_­ CLIENT_V2 sketch. So, our sole BASIC example for the WebMite connects it to a single Z6427 access point and allows remote control of the relay with “0” and “1” keystrokes. You can break out of the program with Ctrl-C if you want to modify it. This can be loaded by downloading the Z6427.UF2 file to a Pico W. The output is shown in Screen 6. Note that because all Z6427s use the “KeyesWifi_ A” access point, this UF2 file has OPTION WIFI set to use that access point name, so it should just work. Software for the XC3804 The XC3804 only creates an access point and does not have the option to connect to other access points, so there is only one Arduino example for it, named XC3804_CLIENT. It works in much the same fashion as the Z6427_ CLIENT software and connects to the Relay. You can then control the relay over its serial port by sending “0” or “1”. As expected, the logic is reversed, so “0” will energise the relay (and the LED will come on), while “1” will power off the relay. Screen 7 shows the serial data produced by this sketch. Improved firmware These two relays have handy features but could benefit from some improvements. In particular, neither can connect to a pre-existing WiFi network, which is what we expect most people to do, especially if they wish to interact with devices on the wider internet. The Z6427’s habit of toggling the relay as it powers up might be sufficient to rule it out of some critical Screen 6: we also created a version of the Z6427_CLIENT software in BASIC for the WebMite, which runs on the Raspberry Pi Pico W hardware. Screen 7: like the Z6427_CLIENT software, XC3804_CLIENT connects to the access point that the Relay creates. Since the XC3804 uses the HTTP protocol, it can also be operated using a computer and browser. 48 Silicon Chip Screen 8: our DUPLEX_RELAY_ FIRMWARE_MDNS firmware can be loaded onto the Z6427 or XC3804 Relays to improve the interface. Our firmware serves up the web page shown here and allows it to connect to an existing WiFi network, such as a home access point. Other information shown allows the Relay to be uniquely identified for later use. Australia's electronics magazine applications, but otherwise, its numerous interfaces are pretty handy. The XC3804’s HTTP interface is very easy to use, particularly for testing purposes, as any computer with a browser can operate it. The lack of a secure access point means it can’t be used with the WebMite. With these aspects in mind, we decided to write our own firmware to work with both module types. Our Clayton’s GPS Time Source article had details about wiring up the ESP-01 module for reprogramming. We have reproduced the figure from that article (Fig.6 here) as it shows the critical details of how to connect the USB/serial adaptor to the ESP-01 via a breadboard for programming. Our improved firmware was also written with the Arduino IDE; the sketch is named DUPLEX_RELAY_ FIRMWARE_MDNS. We have also exported a BIN file you can program directly into the ESP-01 (or other ESP8266 board) with the free ESPFlashDownloadTool software. The ESPFlashDownloadTool software can be downloaded from: siliconchip.au/link/abpv That link is also provided on the Altronics Z6427 product page. The BIN file (and any other BIN files for ESP8266 boards) should be programmed to address 0x000000. Altronics sells the ESP-01 module separately as the Z6360 (siliconchip. au/link/abpy), so you can experiment with this without modifying the ESP01 module that comes with the WiFi Relay Module if you prefer. This firmware provides the same outputs as expected by the Altronics Z6427 and Jaycar XC3804 Relays, so an ESP-01 module programmed with this firmware can be used in either. Simply remove the original ESP-01 and replace it with one programmed with our firmware. Briefly, the updated firmware adds interfaces to allow it to connect to a specific WiFi network. That will enable the relay to connect, for example, to your home WiFi network. Naturally, the selected access point is saved for automatic connection in the future. Some basic diagnostic data is now available via a serial terminal at 9600 baud. This baud rate is necessary to match the rate used by the ESP-01 when it communicates with the second microcontroller on the XC3804 module. siliconchip.com.au Fig.6: this is how you can connect a USB/serial adaptor to an ESP8266 module to reprogram it. The breadboard is mainly needed so you can connect the required pull-up resistors. Like the Jaycar XC3804, an open access point is created, this time with the name “relay”. A DNS server means you can browse to http://relay.setup to easily access the configuration. Screen 8 shows the web page that is displayed. You can test the operation of the Relay by using the OPEN and CLOSE buttons on the web page. You can also set the WiFi SSID and password using the text entry boxes. The information at the bottom of the page includes the IP address of the Relay once it has connected to another network. The HOST and MDNS fields are unique names based on the unique MAC (hardware) address of the ESP01 module. They can be used later to identify each Relay as they should never change, even if the IP address changes. A password can be entered in the LOCK password field to prevent the SSID and password from being modified by someone accessing the Relay’s access point. Re-entering the LOCK password will unlock the Relay. Like any such application, physical access to the relay means that any security measures can be broken, such as by reprogramming the module or reading out data from the flash memory. So we don’t claim that the Relay is invulnerable to security issues, but this small measure should help. The same page is also served up when the Relay has connected to another access point, so you should be able to check operation by browsing to the IP address shown (while connected to the programmed SSID) and confirming that you see the same host address and that the Relay can be controlled in the same fashion. siliconchip.com.au To configure multiple Relays, you should power on each in turn. When each one comes up, access its “relay” access point and configure it to access your preferred WiFi network. Note the IP address and HOST/MDNS fields, then set the LOCK password and power off the Relay before configuring the next. Depending on your access point’s settings, the IP addresses might change, but the HOST/MDNS will not. You can then access the Relays via the following client software. Client control A functional test can be made using the DUPLEX_AP_CLIENT sketch. This connects to the “relay” WiFi network and accesses the http://relay.setup page to control the relays. It is controlled from a serial terminal. It works in the same fashion as the XC3804_CLIENT software seen in Screen 7. Indeed, it is much the same code-wise apart from the different access point and web page addresses. For a more comprehensive control program, use the DUPLEX_STA_­ CLIENT_WEBSERVER sketch. It also has a serial control interface, allowing it to connect to your WiFi network and scan for Relays. On start-up, the sketch scans for networks and prompts you for a password to allow a connection to your home network. This network is saved in emulated EEPROM for future use. You will then see a menu like Screen 9. Both the DUPLEX_RELAY_FIRMWARE_MDNS and DUPLEX_STA_ CLIENT_WEBSERVER sketches implement the mDNS (multicast domain name server) protocol. The Relays are identified by their MDNS names which are displayed in their individual configuration web pages. After a Relay scan (triggered by the “Y” command), any Relays found are saved to emulated EEPROM and can be selected by choosing their letter code (A, B, C etc). They can be operated by typing “0” or “1”. The DUPLEX_STA_CLIENT_WEBSERVER sketch also serves up a web page at the IP address that it prints on the serial terminal. Screen 11 shows a typical display, which, as you can Screen 9: the DUPLEX_ STA_CLIENT Arduino sketch provides a much more advanced control interface. The mDNS protocol allows other Relays to be found by scanning, and individual Relays can be saved and controlled independently. Australia's electronics magazine January 2024  49 The Altronics Z6427 (left) and Jaycar XC3804 (right) shown enlarged for clarity. see, will allow you to scan and control Relays on your local network. BASIC code We’ve also provided a BASIC version (for the WebMite) of this sketch. It is called DUPLEX_STA_CLIENT and works like its Arduino equivalent, although it lacks the web server interface. The UF2 can be loaded onto a blank Pico W to turn it into a WebMite already programmed with this software. However, you will still need to manually configure the OPTION WIFI parameter to connect to your preferred network at the command prompt. Since WebMite BASIC does not implement the mDNS protocol, it has to work slightly differently. It accesses the web page that the Relay generates and looks for the “MDNS:” text to extract the unique identifier. We recommend noting the IP addresses and then using the “V” command to check the relay at that IP address. We’ve included a scan (“Y”) routine, but it is very slow and does not always work. Screen 10 shows the output from the WebMite BASIC program. It can store Relays to non-volatile memory and then control them by typing a letter (A, B, C etc) and “0” or “1”. Fixes We tried adding a capacitor to see if we could eliminate the relay toggling while the WiFi Relay Modules are booting. The capacitors are fitted between the base and emitter of the Q1 transistor in each case. For the Altronics Z6427, around 470μF was required, while the Jaycar XC3804 only required 10μF. Watch the polarity if you try this with electrolytic capacitors. Conclusion Our updated firmware offers significantly improved options for controlling these WiFi Relays, especially as it allows them to connect to a known WiFi network. This simplifies applications where you already have devices connected to an existing network. There is still the limitation of the Altronics Z6427 that the relay contacts close briefly when power is first applied; the Jaycar XC3804 also appears to do so occasionally. For these reasons, we can’t suggest these Relays for interfacing with things Screen 10: although WebMite BASIC does not support the mDNS protocol, our DUPLEX_ STA_CLIENT BASIC program provides similar features (apart from scanning) to the DUPLEX_ STA_CLIENT Arduino sketch. 50 Silicon Chip Australia's electronics magazine Screen 11: the HTTP web server incorporated into the DUPLEX_STA_ CLIENT_WEBSERVER sketch displays a page that allows you to configure and control other WiFi Relays. That means you don’t need to use a serial terminal apart from the initial setup. like automatic gates and garage door openers. A power outage might result in the garage door receiving a spurious open command in the middle of the night! Still, they would be great for controlling low-voltage lights and other decorative applications. They would probably be fine for uses where safety or security is not a concern. All the software we have written for these Relays is also available in compiled form, so you don’t need the Arduino IDE to try them out. For example, we have UF2 files that can be loaded directly onto a Pico W. These are available for all Arduino sketches (except the updated Relay firmware, which is not intended for the Pico W). Our serial control is simple and intended to demonstrate how these devices operate. We expect many readers will add interfaces such as buttons and sensors to automate the operation of the Relays further. Having said that, the web page interface might be sufficient for some readers. As well as the UF2 files for our Pico (Arduino or WebMite) programs, some of the Arduino sketches have also been exported as BIN files, which can be programmed into ESP8266-based boards or modules for testing. We used a D1 Mini for these tests as it has a built-in USB-serial interface. Jaycar sells it as XC3802. Both Relay modules are available for $17.95 at the time of writing. • Altronics Wi-Fi ESP8266 Relay Module For Arduino: siliconchip.au/ link/abpz • Jaycar Smart Wi-Fi Relay Main Board module: www.jaycar.com. au/p/XC3804 SC siliconchip.com.au