ESP8266 setup to talk to an mbed¶

The esp 8266 is a very handy little WiFi module that you can get hold of for a few $ via ebay.

There's a really good wiki page at https://developer.mbed.org/users/4180_1/notebook/using-the-esp8266-with-the-mbed-lpc1768/ with information on how to connect it to an lpc1768 and two test codes.

Whilst playing with this we found it fairly useful to be able to interact with the units via a terminal. In general this is a very good way to check out what it does and get a feel for how the unit behaves.

Our modified terminal passthrough code is here

Using this program you can manually enter the AT commands and observe the responses required to get your esp linked onto a WiFi network and even, somewhat laboriously, send messages to a server.

Power¶

The ESP8266 is a bit of current hog - it can require up to 150mA from the 3.3V supply so generally will not run from an mbeds own regulators (at least its not very reliable when we've tried it here).

Instead a small 3.3V reg running from the 5V USB supply suffices to get it running happily. Something like this seems to work:

NB we now have th MCP1700-330 whose pinout is slightly different. check the MCP website for details at http://ww1.microchip.com/downloads/en/DeviceDoc/20001826C.pdf

You can also put an led and resistor in series across the 3.3v to see if there is any voltage dropout when the unit is transmitting.

The mbed connections look like this (its a top view of the esp8266 here) NB you will need to connect the CH-PD pin high to power up the ESP8266. Sometimes this results in such a drain of power as the ESP turns on that the supply can't cope. Hence if you have any problems check the power first.

Once you've got your ESP8266 connected and powered the simple terminal program above can be really useful.

To get your esp running, upload the code and plug everything in.

Start a terminal and conect it to the mbed (for our linux boxes that's generally something like

where the sudo is required otherwise you can't access the usb ports...

now the fun starts.

you'll probably get some kind of junk coming up on the screen straight away depending on what the esp unit was setup for last time.

to test it out try typing this : AT the board should reply as soon as you push enter with OK

this AT is the attention command that is required as a prefix to any command sent.

send it a few times to check.

Now to get the unit setup properly.

Reset¶

send the following: AT+RST this resets the esp8266 and reads back lots of information about it. The response should be something like this:

AT+RST

OK

ets Jan 8 2013,rst cause:2, boot mode:(3,7)

load 0x40100000, len 1396, room 16 tail 4 chksum 0x89 load 0x3ffe8000, len 776, room 4 tail 4 chksum 0xe8 load 0x3ffe8308, len 540, room 4 tail 8 chksum 0xc0 csum 0xc0

2nd boot version : 1.4(b1) SPI Speed : 40MHz SPI Mode : DIO SPI Flash Size & Map: 8Mbit(512KB+512KB) jump to run user1 @ 1000

�n't use rtc mem data r��rl��� Ai-Thinker Technology Co.,Ltd.

ready

Set the mode¶

ok now set the mode (we want client at the moment) - this means that the wifi module will connect to our router as opposed to becoming a router in its own right... AT+CWMODE=1

which will reply with OK

Connect the unit¶

Now to get the unit online; send this to login to the wifi unit named CWMWIFI with password CWM2016TT AT+CWJAP="CWMWIFI",CWM2016TT"

there will be a slight delay and then a response which is hopefully

WIFI CONNECTED WIFI GOT IP

OK

if it goes wrong you'll get ERROR

If all has gone well you are now online.

Find the IP address¶

It's handy to know what IP address you've ben given so to find out send AT+CIFSR

Reply will be:

+CIFSR:STAIP,"192.168.1.4"

+CIFSR:STAMAC,"5c:cf:7f:1c:0e:ff"

So at this point the esp8266 is registerd on the network and you can now really start testing.

There are two options now: Either you want to be a server or a client.

Server Setup¶

To setup as a server that will respond to requests sent to port 8080 (you can probably choose any in our case but your router / firewall can limit the options sometimes) :

set the unit to multiple connections AT+CIPMUX=1 which should respond with OK then

AT+CIPSERVER=1,8080 which should also respond with OK

What this has done is tell the esp8266 to become a server and accept connections on port 8080. Now if another unit connects to this one (see later) you;ll get a response and be able to respond.

Client Setup¶

This is what to do for a unit tat's going to talk to a server: set the unit to multiple connections AT+CIPMUX=1 which should respond with OK so far so good (and the same as the other version) now to open a connection to our server using connection 4 (there are 5 to choose from thats the point of the multiple connections option above) to a server whose IP address is 192.168.1.4 and is open to connections on port 8080

AT+CIPSTART=4,"TCP","192.168.1.4",8080 after which you are hoping for something like OK CONNECTED although some seems to reply with LINKED

if something goes wrong then you get

ERROR

4,CLOSED

assuming that you got a link you can now send a message: To send the text "Quick Brown Fox" you do this:

AT+CIPSEND=4,14

where the number 4 denotes the connection to send to and the number 14 tells the system how many bytes you want to send.

the response to this should be

>

and at this point you can just type the message

Quick Brown Fox

as soon as you type the 14th character("x") the message will be sent

Other useful info¶

• if you send a command to the esp8266 too soon then it will fail and the unit returns busy p...
• If you server times out you can extend its timeout time by sending AT+CIPSTO=xxxx where xxxx is a number between 0 and 7200 and is equal to the timeout delay. by default this is only 180s when you first use the esp8266 whihc is a little short. if you want your connection kept alive then extend this. if the number xxxx=0 the timeout is infinity but this is potentially problematic in some situations.

Example communication¶

AT+CIPSTART=4,"TCP","192.168.1.3",8080

4,CONNECT

OK

AT+CIPSEND=4,14

OK > The Quick Fox

Recv 14 bytes

SEND OK

server response

+IPD,4,5:?The Quick Fox

Talking to the internet¶

Its possible, once the wifi is running that you would want to talk to websites over the wider internet. First one needs a wifi router thats on the web of course but assuming that this is available you can connect your esp to it and then make connections to the wider world.

First you need to tell your esp to make a connection to the website you want. This assumes you already logged into the wifi on it etc.

This example will get the time in JSON format. See http://www.jsontest.com/#date for more details.

We will use a single connection.

AT+CIPMUX=0

AT+CIPSTART="TCP","time.jsontest.com",80

This should reply with something encouraging like CONNECTED or LINKED

Now the fun starts - web servers will not reply to you unless you correctly terminate your commands. If you just send some bytes to one it will generally ignore you unless the end of the command string is terminated with <CR><LF><CR><LF> - yes thats right - twice.

The string you need to send is

GET / HTTP/1.1 <CR><LF>

host: time.jsontest.com <CR><LF>

<CR><LF>

The commands to send is therefore

"AT+CIPSEND=4,41\r\nGET / HTTP/1.\r\nhost: time.jsontest.com\r\n\r\n"