After trying the simple example on the previous page, you can switch to this code to try out Bluetooth LE functionality using the Adafruit Bluefruit LE Connect app on your iOS or Android device.
See this guide to get the app installed and set up.
To use with CircuitPython, you need to first install a few libraries, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, open the directory Baudot_tty/baudot_tty_ble/ and then click on the directory that matches the version of CircuitPython you're using and copy the contents of that directory to your CIRCUITPY drive.
Your CIRCUITPY drive should now look similar to the following image:
# SPDX-FileCopyrightText: 2020 John Park for Adafruit Industries
#
# SPDX-License-Identifier: MIT
### Baudot TTY Message Transmitter
### Bluefruit Connect UART mode to send messages to CLUE for audio
### tramsission to TTY machine.
### The 5-bit mode is defined in ANSI TIA/EIA-825 (2000)
### "A Frequency Shift Keyed Modem for use on the Public Switched Telephone Network"
import time
import math
import array
import board
import audiopwmio
from audiocore import RawSample
from adafruit_ble import BLERadio
from adafruit_ble.advertising.standard import ProvideServicesAdvertisement
from adafruit_ble.services.nordic import UARTService
# BLE radio setup
ble = BLERadio()
uart_server = UARTService()
advertisement = ProvideServicesAdvertisement(uart_server)
ble._adapter.name = "TTY_MACHINE" # pylint: disable=protected-access
# constants for sine wave generation
SIN_LENGTH = 100 # more is less choppy
SIN_AMPLITUDE = 2 ** 12 # 0 (min) to 32768 (max) 8192 is nice
SIN_OFFSET = 32767.5 # for 16bit range, (2**16 - 1) / 2
DELTA_PI = 2 * math.pi / SIN_LENGTH # happy little constant
sine_wave = [
int(SIN_OFFSET + SIN_AMPLITUDE * math.sin(DELTA_PI * i)) for i in range(SIN_LENGTH)
]
tones = (
RawSample(array.array("H", sine_wave), sample_rate=1800 * SIN_LENGTH), # Bit 0
RawSample(array.array("H", sine_wave), sample_rate=1400 * SIN_LENGTH), # Bit 1
)
bit_0 = tones[0]
bit_1 = tones[1]
carrier = tones[1]
char_pause = 0.0 # pause time between chars, set to 0 for fastest rate possible
dac = audiopwmio.PWMAudioOut(
board.A2
) # the CLUE edge connector marked "#0" to STEMMA speaker
# The CLUE's on-board speaker works OK, not great, just crank amplitude to full before trying.
# dac = audiopwmio.PWMAudioOut(board.SPEAKER)
LTRS = (
"\b",
"E",
"\n",
"A",
" ",
"S",
"I",
"U",
"\r",
"D",
"R",
"J",
"N",
"F",
"C",
"K",
"T",
"Z",
"L",
"W",
"H",
"Y",
"P",
"Q",
"O",
"B",
"G",
"FIGS",
"M",
"X",
"V",
"LTRS",
)
FIGS = (
"\b",
"3",
"\n",
"-",
" ",
"-",
"8",
"7",
"\r",
"$",
"4",
"'",
",",
"!",
":",
"(",
"5",
'"',
")",
"2",
"=",
"6",
"0",
"1",
"9",
"?",
"+",
"FIGS",
".",
"/",
";",
"LTRS",
)
char_count = 0
current_mode = LTRS
# The 5-bit Baudot text telephone (TTY) mode is a Frequency Shift Keyed modem
# for use on the Public Switched Telephone network.
#
# Definitions:
# Carrier tone is a 1400Hz tone.
# Binary 0 is an 1800Hz tone.
# Binary 1 is a 1400Hz tone.
# Bit duration is 20ms.
#
# Two modes exist: Letters, aka LTRS, for alphabet characters
# and Figures aka FIGS for numbers and symbols. These modes are switched by
# sending the appropriate 5-bit LTRS or FIGS character.
#
# Character transmission sequence:
# Carrier tone transmits for 150ms before each character.
# Start bit is a binary 0 (sounded for one bit duration of 20ms).
# 5-bit character code can be a combination of binary 0s and binary 1s.
# Stop bit is a binary 1 with a minimum duration of 1-1/2 bits (30ms)
def baudot_bit(pitch=bit_1, duration=0.022): # spec says 20ms, but adjusted as needed
dac.play(pitch, loop=True)
time.sleep(duration)
# dac.stop()
def baudot_carrier(duration=0.15):
# Carrier is transmitted 150 ms before first character is sent
baudot_bit(carrier, duration)
dac.stop()
def baudot_start():
baudot_bit(bit_0)
def baudot_stop():
baudot_bit(bit_1, 0.04) # minimum duration is 30ms
dac.stop()
def send_character(value):
baudot_carrier() # send carrier tone
baudot_start() # send start bit tone
for i in range(5): # send each bit of the character
bit = (value >> i) & 0x01 # bit shift and bit mask to get value of each bit
baudot_bit(tones[bit]) # send each bit, either 0 or 1, of a character
baudot_stop() # send stop bit
baudot_carrier() # not to spec, but works better to extend carrier
def send_message(text):
global char_count, current_mode # pylint: disable=global-statement
for char in text:
if char not in LTRS and char not in FIGS: # just skip unknown characters
print("Unknown character:", char)
continue
if char not in current_mode: # switch mode
if current_mode == LTRS:
print("Switching mode to FIGS")
current_mode = FIGS
send_character(current_mode.index("FIGS"))
elif current_mode == FIGS:
print("Switching mode to LTRS")
current_mode = LTRS
send_character(current_mode.index("LTRS"))
# Send char mode at beginning of message and every 72 characters
if char_count >= 72 or char_count == 0:
print("Resending mode")
if current_mode == LTRS:
send_character(current_mode.index("LTRS"))
elif current_mode == FIGS:
send_character(current_mode.index("FIGS"))
# reset counter
char_count = 0
print(char)
send_character(current_mode.index(char))
time.sleep(char_pause)
# increment counter
char_count += 1
while True:
print("WAITING...")
send_message("\nWAITING...\n")
ble.start_advertising(advertisement)
while not ble.connected:
pass
# Connected
ble.stop_advertising()
print("CONNECTED")
send_message("\nCONNECTED\n")
# Loop and read packets
while ble.connected:
if uart_server.in_waiting:
raw_bytes = uart_server.read(uart_server.in_waiting)
textmsg = raw_bytes.decode().strip()
print("received text =", textmsg)
send_message("\n")
send_message(textmsg.upper())
# Disconnected
print("DISCONNECTED")
send_message("\nDISCONNECTED\n")
Once you've copied the code.py code file to your CLUE, you can connect from the Bluefruit app to the CLUE device named TTY Machine and then use the UART function to send messages to the CLUE.
The letters will be received by the CLUE and then sent as audio to the TTY machine!
Page last edited January 21, 2025
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