Scanning and conecting to multiple SSIDs

Updated Sep 24

My project has several ESPs running at different locations that collect various data and upload it to an online database.
In production, these will use a wi-fi connection to an internal dongle which provides the 4g connection to a data network, but though each unit has a dongle, at this point I only have one active sim card and telephone network account.

Development takes place in two locations, and remote units are placed in some other locations with access to an internet connection via wi-fi, so I needed a way to connect to any abailable wi-fi network that I had a password for. I also needed this functionality to be seamless, in that I did not want to hardcode the connection function and end up with different code versions depending on location.
This was also important as units are often moved from on location to another, or brought into the office for upgrades, and I wanted them to continue working constantly wherever they were without any user intervention.

So this is what I came up with.

The available SSID and Password pairs are stored in two tuples.

SSID = ('blank', 'TP-Link_AA0B', 'SKYZKJYK', 'FRITZ!Box 7530 SX', 'NOVA_U2G9_A2', 'Gigaclear_2C42')
PASS = ('blank', '12345678', 'AAAAAAA', '5432154321', 'BBBBBBBB', 'abcdefgh')

The first string in each is 'blank' so the connection function can return 0 if no connection found.

import network
SSID = ('blank', ssid1', 'ssid2', 'ssid3', 'ssid4', 'ssid5')
PASS = ('blank', 'pass1', pass2', 'pass3', 'pass4',  'pass5')
station = network.WLAN(network.STA_IF)
station.active(False)

def get_connection(station):
    available_ssid = len(SSID)
	station.active(True)
    station.config(reconnects = 5)
    count = 0
    for x in range(10):
        nets = station.scan()
        for net in nets:
            con = net[0].decode('UTF-8')
            for z in range (available_ssid):
                if SSID[z] == con:
                    ssid = con
                    password = PASS[z]
                    isp = z
                    station.connect(ssid,password)
                    while not station.isconnected():
                        print('.', end="")
                        sleep(1)
                        count += 1
                        if count > 30: return 0          
        Print('WLAN connection to ' + ssid + ' succeeded!')
        #Print(station.ifconfig())
        return isp
        if station.isconnected(): break
        count += 1
        Print(count)
        sleep(2)
    Print('Unable to make connection after ' + str(count) + ' tries.')
    return 0

The first line of the function finds the number of possible SSIDs it could connect to. It scans for all SSIDs in range every 2 seconds 10 times.

On each pass, it checks the SSID of all those found against the list in the tuple SSID. If there is a match, it tries for 30 seconds to connect to it using the corresponding password from the tuple PASS.

Using this function, the only thing you need to change in your code are the possible SSIDs you could connect to in the two tuples at the head of the code, and numerous units could connect to any known router regardless of location, all using the same code.

Links

IDE editors for programming ESP boards.
Micropython editors

Micropython functionality and libraries.
Micropython.org

Find the uPython firmware for your board.
uPython firmware for development boards.

ESP32 uPython modules and function examples.
Quick reference for the ESP32

Finding the MAC address

Scanning and connecting to multiple SSIDs

Using an SD card reader breakout board

ESP32 Real Time Clock

The Deepsleep function

Storing variables in the RTC

RTC Tuning

OTA Updating running software without interuption

Future articles

Communication between ESPs

Using an Adafruit GPS module

Hassle free web communication with urequests.py.