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Tiny Snakes Lesson 2: Wifi

WIFI background

There is a single radio on the ESP8266, but it has some nice features:

  • Client mode (able to connect to access points)
  • AP mode (can provide an access point)
  • Can do both "simultaneously"
  • Raw frames are possible but complicated
  • TCP/IP is mostly dealt with
  • MicroPython has an in-built web server that will provide a REPL prompt
    • We aren't going to play with this really here, there's too many devices here

Dealing with AP mode

The ESP8266 with MicroPython will default to starting up the AP on, so lets deal with turning it off:

>>> import network
>>> ap_if = network.WLAN(network.AP_IF)

ap_if meaning "access point interface" in this case.

To check what state the ap_if is in (I.E. is the AP mode on and broadcasting?)

ap_if.active()
True

To find out what IP settings are currently set:

>>> ap_if.ifconfig()
('192.168.4.1', '255.255.255.0', '192.168.4.1', '8.8.8.8')

Lets setup the client before turning off the AP

Noting that in the following example sta_if is the station, or client, interface. You are basically connecting to a pre-existing wifi. You could put anything into the SSID and Password below, but unless they match the network you won't get into anything

>>> sta_if = network.WLAN(network.STA_IF)
>>> sta_if.active(True)
>>> sta_if.connect('<your ESSID>', '<your password>')
>>> # Loop till we actually get a successful connection
>>> while not sta_if.isconnected():
>>>     pass
...
...
...
>>> sta_if.ifconfig()
('192.168.0.2', '255.255.255.0', '192.168.0.1', '8.8.8.8')
>>> # Now disable AP mode, you don't need it any more
>>> ap_if.active(False)

Sockets

TCP/IP and UDP sockets are availble, so lets go ahead and open one up and see where it gets us.

>>> import socket
>>> addr_info = socket.getaddrinfo("towel.blinkenlights.nl", 23)
>>> addr = addr_info[0][-1]
>>> s = socket.socket()
>>> s.connect(addr)

You now have a connected socket to the remote server, we should likely pull some data

>>> while True:
...     data = s.recv(500)
...     print(str(data, 'utf8'), end='')
...

When you are bored with this you can always < ctrl>+c out to end the loop

>>> s.shutdown(1)
>>> s.close()

So lets move onto something a bit more complicated, like pulling a website down

def http_get(url):
    _, _, host, path = url.split('/', 3)
    addr = socket.getaddrinfo(host, 80)[0][-1]
    s = socket.socket()
    s.connect(addr)
    s.send(bytes('GET /%s HTTP/1.0\r\nHost: %s\r\n\r\n' % (path, host), 'utf8'))
    while True:
        data = s.recv(100)
        if data:
            print(str(data, 'utf8'), end='')
        else:
            break
    s.close()

So lets actually snag the website now

>>> http_get('http://micropython.org/ks/test.html')

Going further

  • Blink the LED on packet TX or RX
  • Blink the LED based on status of events