Merge pull request adafruit#1095 from jedgarpark/baudot-tty

first commit

Author: jedgarpark

Baudot_TTY/baudot_tty.py

@@ -0,0 +1,209 @@
+### Baudot TTY Message Transmitter
+
+### 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
+from audiocore import RawSample
+import audiopwmio
+
+# 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 = 0.1  # 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 tone is transmitted for 150 ms before the
+    # first character is transmitted
+    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:
+    send_message("\nADAFRUIT 1234567890 -$!+='()/:;?,. ")
+    time.sleep(2)
+    send_message("\nWELCOME TO JOHN PARK'S WORKSHOP!")
+    time.sleep(3)
+    send_message("\nWOULD YOU LIKE TO PLAY A GAME?")
+    time.sleep(5)
+
+    # here's an example of sending a character
+    # send_character(current_mode.index("A"))
+    # time.sleep(char_pause)