Follow our handy getting-started guide on CircuitPython and especially the ESP8266 installation page/guide to learn how to install CircuitPython on your ESP8266 Feather

Flash the latest version of CircuitPython (you'll need v 2.2 or higher) and continue to the next step!

Installing and using ampy

We're using the ESP8266 Feather which means it has lots of memory and Internet capability. We use the Internet part to get the current time. However, this Feather is not as easy to use as the SAMD series, as it does not show up as a disk drive!

You'll need to use ampy to install the circuitpython scripts!


Once you've gotten ampy working save the following to your computer as and upload it so that you don't have to turn off the os debug output via REPL anymore

import esp

Install libraries

You'll need a bunch of libraries to get the OLED working. Use ampy to create a directory called lib

Then download the latest library bundle

You'll need to upload adafruit_ssd1306.mpy, and the adafruit_bus_device and adafruit_register folders to the lib folder. Then check with ampy's ls command to verify all  your files are in place!

Main Sketch

Now you can download the following script to your computer and save it as

Don't upload it via ampy yet! The current file has fake tokens in it that need to be set!

# SPDX-FileCopyrightText: 2017 Limor Fried for Adafruit Industries
# SPDX-License-Identifier: MIT

import time

import adafruit_ssd1306
import bitbangio as io
import board
import network
import ntptime
import ubinascii
import uhashlib

# pylint: disable=broad-except

# example
totp = [("Discord ", 'JBSWY3DPEHPK3PXP'),
        ("Gmail   ", 'abcdefghijklmnopqrstuvwxyz234567'),
        ("Accounts", 'asfdkwefoaiwejfa323nfjkl')]
ssid = 'my_wifi_ssid'
password = 'my_wifi_password'

TEST = False  # if you want to print out the tests the hashers
ALWAYS_ON = False  # Set to true if you never want to go to sleep!
ON_SECONDS = 60  # how long to stay on if not in always_on mode

i2c = io.I2C(board.SCL, board.SDA)
oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)

# Gimme a welcome screen!
oled.text('CircuitPython', 0, 0)
oled.text('PyTOTP Pal!', 0, 10)
oled.text(' <3 adafruit <3 ', 0, 20)

EPOCH_DELTA = 946684800  # seconds between year 2000 and year 1970
SECS_DAY = 86400

SHA1 = uhashlib.sha1

if TEST:
    print("SHA1 test: ", ubinascii.hexlify(SHA1(b'hello world').digest()))
    # should be 2aae6c35c94fcfb415dbe95f408b9ce91ee846ed

# HMAC implementation, as hashlib/hmac wouldn't fit
# From
def HMAC(k, m):
    SHA1_BLOCK_SIZE = 64
    KEY_BLOCK = k + (b'\0' * (SHA1_BLOCK_SIZE - len(k)))
    KEY_INNER = bytes((x ^ 0x36) for x in KEY_BLOCK)
    KEY_OUTER = bytes((x ^ 0x5C) for x in KEY_BLOCK)
    inner_message = KEY_INNER + m
    outer_message = KEY_OUTER + SHA1(inner_message).digest()
    return SHA1(outer_message)

if TEST:
    KEY = b'abcd'
    MESSAGE = b'efgh'
    print("HMAC test: ", ubinascii.hexlify(HMAC(KEY, MESSAGE).digest()))
    # should be e5dbcf9263188f9fce90df572afeb39b66b27198

# Base32 decoder, since base64 lib wouldnt fit

def base32_decode(encoded):
    missing_padding = len(encoded) % 8
    if missing_padding != 0:
        encoded += '=' * (8 - missing_padding)
    encoded = encoded.upper()
    chunks = [encoded[i:i + 8] for i in range(0, len(encoded), 8)]

    out = []
    for chunk in chunks:
        bits = 0
        bitbuff = 0
        for c in chunk:
            if 'A' <= c <= 'Z':
                n = ord(c) - ord('A')
            elif '2' <= c <= '7':
                n = ord(c) - ord('2') + 26
            elif c == '=':
                raise ValueError("Not base32")
            # 5 bits per 8 chars of base32
            bits += 5
            # shift down and add the current value
            bitbuff <<= 5
            bitbuff |= n
            # great! we have enough to extract a byte
            if bits >= 8:
                bits -= 8
                byte = bitbuff >> bits  # grab top 8 bits
                bitbuff &= ~(0xFF << bits)  # and clear them
                out.append(byte)  # store what we got
    return out

if TEST:
    print("Base32 test: ", bytes(base32_decode("IFSGCZTSOVUXIIJB")))
    # should be "Adafruit!!"

# Turns an integer into a padded-with-0x0 bytestr

def int_to_bytestring(i, padding=8):
    result = []
    while i != 0:
        result.insert(0, i & 0xFF)
        i >>= 8
    result = [0] * (padding - len(result)) + result
    return bytes(result)

# HMAC -> OTP generator, pretty much same as

def generate_otp(int_input, secret_key, digits=6):
    if int_input < 0:
        raise ValueError('input must be positive integer')
    hmac_hash = bytearray(
    offset = hmac_hash[-1] & 0xf
    code = ((hmac_hash[offset] & 0x7f) << 24 |
            (hmac_hash[offset + 1] & 0xff) << 16 |
            (hmac_hash[offset + 2] & 0xff) << 8 |
            (hmac_hash[offset + 3] & 0xff))
    str_code = str(code % 10 ** digits)
    while len(str_code) < digits:
        str_code = '0' + str_code

    return str_code


# Set up networking
sta_if = network.WLAN(network.STA_IF)

oled.text('Connecting to', 0, 0)
oled.text(ssid, 0, 10)

if not sta_if.isconnected():
    print("Connecting to SSID", ssid)
    sta_if.connect(ssid, password)
    while not sta_if.isconnected():
print("Connected! IP = ", sta_if.ifconfig()[0])

# Done! Let them know we made it
oled.text("IP: " + sta_if.ifconfig()[0], 0, 20)

# Get the latest time from NTP
t = None
while not t:
        t = ntptime.time()
    except Exception:

# NTP time is seconds-since-2000
print("NTP time: ", t)

# But we need Unix time, which is seconds-since-1970
print("Unix time: ", t)

# Instead of using RTC which means converting back and forth
# we'll just keep track of seconds-elapsed-since-NTP-call
mono_time = int(time.monotonic())
print("Monotonic time", mono_time)

countdown = ON_SECONDS  # how long to stay on if not in always_on mode
while ALWAYS_ON or (countdown > 0):
    # Calculate current time based on NTP + monotonic
    unix_time = t - mono_time + int(time.monotonic())
    print("Unix time: ", unix_time)

    # Clear the screen
    y = 0
    # We can do up to 3 per line on the Feather OLED
    for name, secret in totp:
        otp = generate_otp(unix_time // 30, secret)
        print(name + " OTP output: ", otp)  # serial debugging output
        oled.text(name + ": " + str(otp), 0, y)  # display name & OTP on OLED
        y += 10  # Go to next line on OLED
    # Display a little bar that 'counts down' how many seconds you have left
    oled.framebuf.line(0, 31, 128 - (unix_time % 30) * 4, 31, True)
    # We'll update every 1/4 second, we can hash very fast so its no biggie!
    countdown -= 0.25

# All these hashes will be lost in time(), like tears in rain. Time to die

Set Up Networking

Before uploading, change these two lines to your network SSID and password

ssid     = 'my_wifi_ssid'
password = 'my_wifi_password'

Set Up Tokens

You'll also need to get 2 factor "authenticator tokens/secrets". Each site is a little different about how it does this.

For example, when you set up GMail for 2FA it will show you a QR code like this:

This is not the real token from my gmail

Which is great for phones. For us, we need the base32-encoded token. Click the Can't Scan It? link or otherwise request the text token. You'll get a page like this

This is not the real token from my gmail

That string of letters and numbers may be uppercase or lower case, it may also be 16 digits or 24 or 32 or some other qty. It doesn't matter! Grab that string, and remove the spaces so its one long string like "ra4ndd2utltotseol564z3jijj5jo677" Note that the number 0 and number 1 never appear so anything that looks like an O, l or an I is a letter.

Now edit this section of the code, you can display up to 3 accounts on a Feather OLED. If you pad the name with spaces the numbers will be right-justified but its not important, I'm just picky

totp = [("Discord ", 'JBSWY3DPEHPK3PXP'), # exmple
        ("Gmail   ", 'abcdefghijklmnopqrstuvwxyz234567'),
("Accounts", 'asfdkwefoaiwejfa323nfjkl')]

If you want to test the setup first, you can keep the Discord entry which is the "PyOTP" example token. Then scan this with your phone in Authy or Google Authenticator

Test It Out!

OK once you've set everything up lets test!

Run the program directly on the Feather with OLED attached using ampy --port portname run

You'll see it connect to your local network, get the time via NTP, then calculate and display OTP codes both on the OLED and on the serial port (you'll need to wait till the program is done to see the serial output)

Check against your phone to make sure the codes are correct. Once you're satisfied, tweak the two lines to change the behavior

ALWAYS_ON = False  # Set to true if you never want to go to sleep!
ON_SECONDS = 60 # how long to stay on if not in always_on mode

Then finalize by uploading with ampy's put command

This guide was first published on Dec 30, 2017. It was last updated on Nov 28, 2023.

This page (Software) was last updated on Nov 28, 2023.

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