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The $5 WiFi Server By Geoff Graham This is something that you will find hard to believe . . . a WiFi module which includes the 2.4GHz transmitter and receiver, the aerial, a full TCP/IP protocol stack, a web server and everything else that you need to add wireless Internet connectivity to your next Micromite or microcontroller project. And it costs just $5! L OW-COST WiFi modules based on the ESP8266 chip are now available from the Chinese company Espressif Systems Inc. These modules can be purchased from many suppliers on eBay and other sites on the Internet for prices ranging from $4 to $6; and that often includes free postage or freight. The ESP8266 module connects to your microcontroller via a serial link and can be used to serve up web pages, send data to Internet services like Twitter, send emails and so on. So for a very small outlay, you can add a sophisticated level of communications to your next project. The ESP8266 itself is an impressive little chip. It measures just 5 x 5mm and contains a complete WiFi transceiver including the transmitter, receiver, integrated TR switch, balun, low-noise receiver, power amplifier and matching antenna network. It meets the requirements of the 802.11 b/g/n standards, including full encryption, so it will easily integrate with your current network. The ESP8266 needs very few external components. The reference design requires just three capacitors, one resistor, a flash memory chip and a 24MHz crystal. Many suppliers in China have fully-built modules using this design and all you need to do is connect the module to your microcontroller and supply power. In addition to the WiFi transceiver, the chip also houses a 32-bit processor which is used to run the TCP/IP protocol stack. This includes high level Internet protocols such a web (HTTP) server, P2P Wi-Fi Direct, infrastructure base station mode and softAP mode. The ESP8266 is intended to capitalise on the Internet-of-Things (IoT) concept which posits that everything, from the smallest gadget to the largest appliance, will in future be connected to the Internet in some way. For the ordinary experimenter it opens up a world where easy connectivity to the Internet is well within reach. Micromite in the garden Fig.1: you should receive something like this if you connect to our “Micromite Garden Webserver” using the URL: http://garden.geoffg.net It gives you the time according to the server’s internal clock and the current temperature and humidity. It is intended as a demonstration of what you can do using the Micromite and an ESP8266 module. 30  Silicon Chip As a demonstration of what you can do with this module we have placed a Micromite and an ESP8266 module in a garden. This monitors the current temperature and humidity in the garden and serves this data as a web page via WiFi to an access point and then via a router to the Internet. It is only a simple example but if you would like to see the output of a combined Micromite and ESP8266 siliconchip.com.au Fig.2: these are the connections to the most common version of the ESP8266 module which has an on-board antenna. Note that not all modules have the Power Down and Reset pins connected (this mostly applies to older versions of the module). This is our “Micromite Webserver In The Garden”. It may not look pretty but it was only built as a proof of concept. It includes a 28-pin Micromite, ESP8266 module, a real time clock, DHT22 temperature/humidity sensor and a USB-Serial bridge. Note that this location is sheltered from the rain. web server, you can connect to our demonstration server by entering the following URL into the address bar of your browser: http://garden.geoffg. net You should receive a web page as shown in Fig.1. The program running on the Micromite uses a combined temperature/ humidity sensor along with a real-time clock and is a good demonstration of how to implement a web server using the ESP8266 module. The full MMBasic program is available for download from the SILICON CHIP website and if you intend to implement a web server it would make an excellent starting point. The Micromite was featured in the May 2014 issue of SILICON CHIP. In case you missed that issue, the Micromite is a single 28-pin or 44-pin microcontroller that runs a powerful BASIC interpreter. You can control up to 33 I/O pins and communicate with other chips using I2C, serial, SPI and other protocols. In this case, communication with the ESP8266 is via standard serial. Module variations These modules are tiny but they pack a punch. They include the WiFi transmitter and receiver, antenna switching and matching network, WiFi 802.11 a/b/n compatibility, a TCP/IP protocol stack and a web server. When connected to a microcontroller you can serve web pages, send emails and log data onto “the cloud”. The larger unit has the antenna on the PCB while the smaller unit uses an external antenna. Note: modules shown larger than life size. siliconchip.com.au There are a many versions of the ESP8266 module in circulation. The most common is illustrated in Fig.2. It has eight connections which include power, serial transmit/receive, a Power Down pin, a Reset pin and two general purpose input/output pins. This module includes its own aerial etched onto the PCB and this feature makes it quite easy to work with. The only issue with this module is that the arrangement of the connecting pins makes it impossible to plug it into a standard solderless breadboard. So you will need to solder wires to the pins or use jumper leads to connect to a breadboard. Another common version is illustrated in Fig.3. This has just four connecting pins (two for the power and two for the serial interface). Fortunately, these pins have a 0.1-inch spacing which is breadboard friendly. Fig.3: this diagram shows the connections to the version of the ESP8266 module without an inbuilt antenna. The antenna connection is via a miniature U.FL connector and these are common in WiFi access points and routers that employ an externally mounted antenna (you may be able to salvage these parts from an old WiFi router or modem). The module is intended for use with an external aerial and there is a miniature U.FL connector on the board for this purpose (also referred to as an IPEX, IPAX, IPX, MHF, UMCC or AMC type connector). Suitable aerials can be purchased on eBay and the U.FL connector is common in WiFi access points and routers that employ externally mounted aerials – so you may be able to salvage a complete aerial and connector from a discarded access point. As you would expect, with a decent antenna, this module has a far greater range than the version with a PCB antenna. There are other variations of the ESP8266 module with different connecting pads but the above two are the most common The good & the bad The ESP8266 modules on offer are quite powerful but they do come with some issues (or perhaps we should say “challenges”). The ESP8266 chip itself is mostly documented in Chinese. December 2014  31 Fig.4: this is how you could connect an ESP8266 module to the COM1 serial port on a 28-pin Micromite. We have shown the Power Down and Reset pins on the module connected to logic high but if your module uses these pins, you could connect them to the Micromite so that it would have more control over the module. There are some (translated) English data sheets but in general they are brief and do not tell the full story. The firmware (TCP/IP, server, etc) that runs on the 32-bit processor integrated on the chip is what most users will interact with and unfortunately this is also poorly documented. As a result you will need to be adept at trawling the Internet and discovering facts and techniques that others have painfully learnt. Hopefully, what we have to tell you in the following pages will also make that task somewhat easier. You should also refer to the side panels. One lists some of the more relevant commands recognised by the module and the other lists relevant ESP8266 websites where you can find much more information. Connecting up The ESP8266 requires a well-regulated 3.3V supply and it can draw quite a lot of current, especially in transmit mode. Normally, the current requirement varies from 10-70mA when the module is idling or just receiving but it can jump to over 200mA during transmit. So a solid 3.3V 300mA supply is a must. The module has a serial interface running at 115,200 baud with the standard settings (eight bits of data, one stop bit and no parity). This is a TTL level signal (idle is voltage high) and it uses 3.3V signalling levels. These perfectly match the Micromite’s COM1 serial port so the two make a great pair. Do not try to connect the ESP8266 module to a microcontroller running at 5V or to an RS232 interface without a level translator. The voltages on these interfaces will exceed 3.3V and could easily destroy your module. Controlling the ESP8266 To control the operation of the ESP8266 module, the microcontroller will need to send commands over the serial link and will receive acknowledgements and data in return. Communicating is straightforward; all commands sent from the microcontroller begin with the letters “AT” and the module replies with “OK” or “ERROR” or the data that you have requested (rather like the Hayes modems in the past). The Tx (transmit) pin on the module should connect to the Rx (receive) pin on the microcontroller and Rx on the module should connect to Tx on the microcontroller. The Reset and Power Down pins (if your module has them) should be connected to the 3.3V supply. The other (general purpose) pins can be left unconnected. Fig.4 illustrates a typical connection for the 28-pin Micromite. Note that older versions of the module leave the Power Down or Reset pins uncon- nected or use them for general purpose I/O – so you may need to experiment with these two connections (see the accompanying panel for a website that identifies the differences). If your module does have a Power Down pin, it is important that this pin is pulled high by connecting it to the power (3.3V) pin. If it is left floating, the module will power down by default. For the purpose of experimentation you can connect the module via a USBto-Serial bridge and type in commands directly from your computer. First steps In the following discussion, we will avoid listing a lot of programming code. Not only is it boring but it is also much easier to download a program than to type it in. The main program that you will want to refer to is our example of a web server running on the Micromite (in the garden!). This can be downloaded from the SILICON CHIP website. In order to get started with the ESP8266, you need to type in some commands and observe the result. If you are using the Micromite, the easiest way to do this is to use the small program shown in Fig.5. This will turn your Micromite into a simple terminal where anything that you type into the Micromite will be sent to the ESP8266 module and anything it sends back will be sent out from the console to your screen. When you first apply power to the ESP8266 module, the current should jump to about 67mA while the module sniffs the air and then drop down to 10-30mA. Run the terminal program on your Micromite (or connect in some other way) and try typing in: AT When you hit Enter, the module should return with OK. This is a big step and once you are communicating you can get on with testing how the module will respond to your commands. By the way, all commands should be in upper case, should not contain any Issues Getting Dog-Eared? Keep your copies safe with these handy binders REAL VALUE AT $14.95 PLUS P & P Order now from www.siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number or mail the order form in this issue. *See website for overseas prices. 32  Silicon Chip siliconchip.com.au spaces and are all terminated by the Enter key. If you enter an invalid command the module will respond with ERROR, otherwise you should see OK. The next stage is to tell the module to act as both a client and access point. The command is: AT+CWMODE=3 The module should reply with a simple OK. Then you need to reset the module. Why you need to do this is uncertain and not documented but we have found that it is a necessary step. You reset the module with the command: AT+RST You should get an OK followed by a dump of data half a second later. You can ignore this data as it just lists details of the firmware running on the module. At this point you can do some useful things. For example, try listing the WiFi access points in your area. The command is AT+CWLAP and in return you will get something like this: +CWLAP:(0,””,0) +CWLAP:(3,”BigPond9B8A1D”,-86) +CWLAP:(2,”wifhubs”,-85) +CWLAP:(4,”wifhubs_2GEXT”,-77) +CWLAP:(4,”dlink-281D”,-91) +CWLAP:(4,”Baas DSL-2890AL”,-90) In this case the module has sniffed out the WiFi access points in adjacent offices as well as the one we want to connect to. The first digit after the opening bracket is the security protocol that the access point is using (0 = open, 1 = WEP, etc). The second field is the network name (or SSID) of the access point and the third field is the signal strength. Common Commands Recognised By The ESP8266 Module AT Checks that the module is alive. The response should be OK. AT+RST Reset the module. It will first respond with OK followed by a dump of information related to the firmware. AT+GMR Returns the version number of the firmware. AT+CWMODE=n Sets the mode of operation according to the number n. Where 1 is a WiFi client, 2 is an access point and 3 is both client and access point. Note that as an access point the module has limited functionality (no DHCP, etc). AT+CWLAP Will list the currently available access points in the location. AT+CWJAP=”SSID”,”passwd” Will join a network where SSID is the access point name and passwd is the password. Both must be surrounded by quotes. AT+CWQAP Will close the current connection to an access point. AT+CIFSR Will return the IP address assigned to the module. AT+CIPMUX=n Will configure the module for multiple connections according to the number n. Where 0 is single connection mode and 1 is multiple connections mode. AT+CIPSERVER=n,nn Will start a server. If n is 0 if the server is to be disabled or 1 if it is to be enabled. nn is the port number. WEB browsers default to port 80. When a connection is established the module will send “Link” followed by the data offered by the remote browser. AT+CIPSEND=n,nn Will send data to a remote client that has connected to the server. n is the id number of the transport connection (normally zero but it can be some other number if two clients have connected simultaneously). nn is the length of the data to send including any terminating carriage return and line feed characters. The module will prompt with “>” then the microcontroller should send the data followed by carriage return and line feed. Connecting to your network AT+CIPCLOSE=n Close the connection n (normally this is zero). This is should used after all the data has been sent to the client. AT+CWJAP=”SSID”,”passwd” Note: most commands acknowledge with OK or ERROR. There are many more commands that the module will recognise. For a full list, consult the links in the side box. To connect to your WiFi access point, use the following command: where “SSID” is the broadcast name of your WiFi access point and “passwd” is the password for access. Note that there should not be any spaces and the quotes should be retained as shown. If the connection is made, the module will return with OK. If something has gone wrong, you will receive the message ERROR. You could experience some difficulty here as the access point might reject the connection. Possible reasons include incorrect case in the SSID or password, the security set-up of the access point siliconchip.com.au (ie, if only certain MAC addresses are permitted access), the inability of the module to get an IP address from the router because the router is not running DHCP or simply the module being too far from the access point. Once you have connected to your network you can try the command: AT+CIFSR This will return with the IP address that your access point assigned to the module, eg, 192.168.0.109. Note that this command is one of only a few that do not return with OK. To verify that the module is “on the air”, you can ping it from your PC. In the case of a Windows computer, you can call up a command window and and enter the ping command and the IP address. As an example, enter the following at the command prompt: ping 192.168.0.109 You should see the ping packets as they are sent to the module and the December 2014  33 Reference Links For The ESP8266 Home page of Espressif Systems Inc, the designers of the ESP8266: https://espressif.com/ An English version of the data sheet for the ESP8266 chip: https://nurdspace.nl/File:ESP8266_Specifications_English.pdf Description of the module and the commands that it will accept: http://www.electrodragon.com/w/Wi07c and https://nurdspace.nl/ESP8266 How to tell if your module has a Power Down and a Reset pin: http://www.xess.com/blog/esp8266-is-alive/ How to update the firmware: http://blog.electrodragon.com/cloud-updating-your-wi07c-esp8266-now/ A community forum focused on the ESP8266: http://www.esp8266.com Search eBay for sellers of modules based on the ESP8266: http://www.ebay.com/sch/i.html?&_nkw=ESP8266 response times as the module returns the pings. The module will remember all the previous set-up steps, even when the power is cycled. So, when you next apply power, it will automatically connect to your WiFi access point and get an IP address. Most access points/routers will try to assign the same address each time your module connects but this is not guaranteed. To ensure that the address of the module doesn’t change, you should go into your router set-up and assign a fixed IP address to the module based on its MAC address. You need to do this because the module does not have a network name, only an IP address and by making sure that this address does not change you will always be able to find it on your network by using the IP address. Starting the web server The first stage of setting up a web server is to tell the module to accept multichannel connections. The command is: AT+CIPMUX=1 The module should reply with a simple OK. You need to then tell the module to act as a server for port 80, which is the default port used by web browsers. This is done with the AT+CIPSERVER command as follows: AT+CIPSERVER=1,80 The module will respond with OK then listen for incoming connections on that port number. When a remote computer does make a connection, the module will send a line containing 34  Silicon Chip the single word “Link” to the microcontroller. Following this message, the module will send a series of other lines representing the data transmitted by the remote computer when it connected. This often includes information identifying the operating system and browser but the important part is a line with the word “GET” followed by a path. The path is the web page that the browser is requesting. A simple “/” means that the browser wants the main WEB page while (for example) “/data. html” means that the browser wants the page called “data.html”. If you only want to offer the one page, you can ignore the details and just send your data back. This is done using the AT+CIPSEND command, as follows: AT+CIPSEND=n,nn where n is the channel number and nn is the length of the line of text that will be sent (including the terminating carriage return and line feed characters). The module will respond with “>” which is the prompt to send the actual line of text. When that line has been transmitted, the module will return with: SENT OK The channel number (n) mentioned above is normally zero but the module can handle up to four simultaneous requests and if that happens you will have to note which request you are responding to and use the correct number for n. This is a typical send operation AT+CIPSEND=0,38 > <TITLE>Micromite WiFi Server</TITLE> SEND OK You may send as many lines as you wish by using multiple AT+CIPSEND commands. Each line should be formatted according to the html standard so that they will display correctly in the browser. When you have finished sending the web page, you should close the connection with the command: AT+CIPCLOSE=n where n is the channel number. Rather than go into excessive detail, it will make more sense if you to download the example server code for the “Micromite in the Garden” from the SILICON CHIP website. Using the above discussion as a guide, you can see how a real web server can be implemented. Restarting the module One annoying issue that we did run into is that the ESP8266 can get confused for no particular reason and stop communicating. To overcome this, we used a TI TPS2042B power switch to control power to the module. If the module did not respond, the program would turn off power to the ESP8266 for a short time to clear the fault condition. The MMBasic server program would then initialise the module. Note that if you use this technique, you should also place a 33kΩ resistor in series with the signal going to the module’s Rx pin. This is because the microcontroller will still be driving its Tx line at 3.3V when the module is powered down and the resultant current into the module’s Rx input will destroy it. The resistor will limit this current to a safe value (100µA). Alternatively, if you have a module with a Power Down pin, you can achieve the same result by simply connecting this pin to an output pin on the microcontroller and toggling it low for 200ms when you need to restart the module. It’s possible that a more recent version of the firmware for the ESP8266 will fix the bug that causes it to become non-communicative. However, this technique will still be useful because there are many other things that can go wrong and a brief power down will rescue the server regardless of what difficulty it is in. Beyond a simple web server You can get quite fancy with your web server if you want to. You could format the data in your web page to include variables that the microconsiliconchip.com.au troller is monitoring; eg, temperature, voltages etc. You can also use html FORM tags to create check boxes, radio buttons and push buttons on the web page. When the user selects these items, their browser will send a message to the ESP8266 module which can be interpreted by your server program to turn on a valve, unlock a door or whatever. Using html links, you can have hot links in the web page that link to other pages supplied by your microcontroller or other websites. Nor are you limited to simply serving web pages. Using the ESP8266 module, your microcontroller can get the time from the Internet or the current weather forecast. You can connect to an SMTP server and send emails – eg, to alert you to some fault condition. You can also connect to services like Twitter to upload and log interesting information – eg, the humidity in your greenhouse. There are also websites that specialise in logging data from embedded controllers. A popular service is http://thingspeak.com which will store, graph and present your data for you. Imagine being able to check the temperature trends in your home-brew concoction via your smartphone. And don’t forget that the cost is just $5 for this amazingly capable module. Upgrading the ESP8266 Most ESP8266 modules come with version 00160901 of the firmware. You can discover the version of your module with the command: AT+GMR Some talented individuals on the Internet have created alternative versions of the firmware which include bug fixes and extra features such as the ability to change the baud rate. One especially valuable feature is the capability of putting the module into a transparent mode where any data sent by the remote computer is fed straight through to the microcontroller and vice versa. This means that you can set up an ESP8266 module and connect it to the Micromite’s console. Using telnet, you can then connect to the Micromite via WiFi and edit the program running on it – all from your desktop while the Micromite and ESP8266 module are hidden in a cabinet, in your shed or some other inaccessible location. An accompanying panel contains Terminal Program OPEN “Com1:115200” AS #1 DO PRINT INPUT$(1, #1); PRINT #1, INKEY$; LOOP Fig.5: this simple program will turn your Micromite into a terminal. It will shuffle characters between its console and COM1 (the ESP8266 module) and is useful for experimenting with the module and verifying how it reacts to commands. links to websites that carry upgraded versions of the firmware. To upgrade the module, you need to short one of the GPIO pins to ground and run a program on your computer that will transfer the new firmware via the serial link. The operation is relatively painless and it only takes a minute or so. About the only downside is that the new commands and features are often poorly documented so you will need to engage in some personal experiSC mentation. Enter C ode : SCDEC 20 *Conditions apply Selecte d Items Ends 20 O%FF 15th January 2015 S AV E 4D Systems designs, develops and manufactures intelligent graphics solutions using the latest OLED and LCD technology available, with custom graphics processors that enable both stand alone and host dependent solutions suitable for a very wide range of applications and projects. 4D SYSTEMS TURNING TECHNOLOGY INTO ART www.4dsystems.com.au siliconchip.com.au .com/4DSystemsAU .com/4DSystems December 2014  35