first upload

README

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+JJY.py: sync JJY40-enabled watches and clocks from Python 3
+-----------------------------------------------------------
+This is a Python port of the 7-year old "Project Fukushima" JJY40 emulator
+for syncing longwave-enabled watches and clocks that support this station.
+With the help of any sort of loop antenna (or even headphones or speakers), it
+allows you to adjust your watch without having to be close to the Japanese
+signal. This program follows the JJY timecode specification and modulation
+methods used by the oldest desktop applications for this very purpose, and
+transmits on 13333.(3) Hz, whose 3rd harmonic is the reference frequency,
+40 KHz, but the base frequency here is within the spectrum supported by any
+consumer-grade audio hardware.
+
+== Dependencies ==
+
+JJY.py depends on PyAudio (>=0.2.14) and ntplib (>=0.4.0). Just install them
+by running pip install -r requirements.txt from the project directory. Note
+that installing PyAudio will also pull its PortAudio (>=v19) dependency.
+
+The program has been primarily tested on Python 3.10.
+
+== Usage ==
+
+JJY.py can be run like this:
+
+python jjy.py [-t duration] [-d delta] [-s ntp_server] [-n ntp_version] \
+              [-o tz_offset] [-r sample_rate]
+
+All parameters are optional here:
+
+* -h: display help screen
+* -t: transmission duration in minutes (default 30)
+* -d: manual delta correction in milliseconds (default 0, see below)
+* -o: timezone offset from UTC (in hours, default 9, see below)
+* -r: transmission sampling rate (in Hz, default 48000, only change if this
+      fails to work)
+* -s: specify NTP server to fetch time from (if no server is specified, then
+      local system time is used)
+* -n: specify NTP protocol version to use, default is 4, good for most cases
+
+After running the command, you must enter the synchronization mode on your
+watch/clock (making sure that JJY40 is selected if it's multiband) and put it
+close enough to your (improvised) loop antenna, headphones or speakers. The
+script will fetch the UTC time according to your source, apply the TZ offset,
+then the manual delta offset and then will attempt to start the transmission
+from the closest second. The TZ offset is set to +9 hours by default because
+most JJY-enabled watches/clocks expect the JST time to be sent in order to
+then apply their own timezone correction according to your settings. If your
+watch/clock doesn't have such correction, you can always use this -o flag to
+zero out this offset (with -o 0) and transmit the local time directly onto it.
+In case your equipment, software or time source server introduce any delay to
+the synchronization process, you can add a constant delta (in milliseconds)
+with the -d flag. After the synchronization is successful, you can press the
+Ctrl+C combination or wait until the entire sequence (which is 30 minutes long
+by default, adjustable with -t flag) gets transmitted.
+
+== FAQ ==
+
+- How is this even possible?
+
+To put it simply, to emit any audio signal, electricity has to travel through
+many wires and coils. This inevitably creates electromagnetic interference. If
+we send the signal of a particular constant frequency with enough intensity
+through audio circuits, this interference will turn into radio emission in the
+longwave spectrum, which is exactly what we need for syncing radio-controlled
+clocks and watches. This emission is too weak to cause any harm outside but
+enough to be received by the watch or clock several centimeters apart.
+
+- Which watches/clocks has this been tested on?
+
+Some Casio and Citizen models, including Casio GW-B5600BC, GMW-B5000D and
+Citizen PMD56-2951.
+
+- Is my particular watch/clock model supported?
+
+As long as it can receive JJY40 signal and you know how to make it do this, it
+is automatically supported by JJY.py. At this point, I can surely say that if 
+anything goes wrong, it's not the fault of your watch or your emulator, but 
+something in between: audio setup, antenna setup or the placement of the watch
+relative to the antenna. It might take some trial and error and a great deal
+of patience to make sure everything works as expected.
+
+For most digital Casio models, you can force JJY40 reception by entering one
+of the test menus: press and hold first Light, then Receive and then Mode
+button. Scroll through with the Receive button to ensure that "J 40" is on the
+screen, then start the reception process with the Light button. You should get
+a "JOK" message if the process is successful, or "JNG" if unsuccessful.
+
+- Aren't there enough JJY emulation apps already?
+
+In 2017, there were almost no cross-platform solutions for this, and this was
+the primary reason the Fukushima project started. However, even in 2024, I
+could not find any Python solution for this meant for normal desktop and not
+for Raspberry Pi, Arduino and other embedded platforms. That's why a port of
+the JJY.js library to Python was deemed necessary.
+
+- Are there still any plans for implementing other longwave time protocols?
+
+Maybe. DCF77 and WWVB are of the primary interest.
+
+== Credits ==
+
+Original research, JS library and web demo application by Luxferre, 2017.
+Ported to Python in 2024. Released into public domain with no warranties.

jjy.py

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+#!/usr/bin/env python3
+# JJY.py: a port of jjy.js library and a standalone script
+# to synchronize time on JJY-enabled wristwatches via headphones
+# Depends on pyaudio and ntplib
+# Created by Luxferre in 2024, released into public domain
+
+import pyaudio, ntplib, math, array, time, datetime
+
+OP_FREQ = 40000/3 # emitted frequency, Hz
+
+# BCD and parity calculation helpers
+
+def toBCD(val: int):
+  return (val%10) + ((int(val/10)%10)<<4) + (int(val/100)<<8)
+
+def calc_parity(val: int):
+  i = 0
+  while val != 0:
+    i ^= (val & 1)
+    val >>= 1
+  return i
+
+# internal time representation from unix time
+# only fetches the fields necessary for JJY implementation
+def intreptime(unixtm):
+  res = {}
+  tm = time.gmtime(unixtm)
+  res['year'] = toBCD(tm.tm_year % 100)
+  res['yday'] = toBCD(tm.tm_yday)
+  res['hour'] = toBCD(tm.tm_hour)
+  res['minute'] = toBCD(tm.tm_min)
+  res['second'] = tm.tm_sec
+  # in Python, Monday is 0; in JJY, Sunday is 0
+  res['wday'] = (tm.tm_wday + 1) % 7
+  res['unix'] = int(unixtm) # save the unix time representation
+  return res
+
+# time fetching part (returns JST)
+def fetchtime(params = {}):
+  delta = 0.0
+  offset = 32400
+  if 'delta' in params:
+    delta = float(params['delta']) / 1000
+  if 'offset' in params: # base offset from UTC in seconds
+    offset = int(params['offset'])
+  if 'server' in params and params['server'] is not None: # NTP server set
+    ntpver = 3
+    if 'version' in params:
+      ntpver = params['version']
+    c = ntplib.NTPClient()
+    resp = c.request(params['server'], version=ntpver)
+    unixtm = resp.tx_time
+  else: # use current system time by default
+    unixtm = time.time()
+  unixtm += offset + delta # account for delta
+  return intreptime(unixtm)
+
+# timecode generation part
+# accepts the result of fetchtime function
+def gentimecode(ts):
+  timecode = [2,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,
+    0,0,2,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,2,0,0,0,0,0,0,0,0,0,2]
+  # populate minute
+  timecode[1] = (ts['minute']>>6)&1
+  timecode[2] = (ts['minute']>>5)&1
+  timecode[3] = (ts['minute']>>4)&1
+  timecode[5] = (ts['minute']>>3)&1
+  timecode[6] = (ts['minute']>>2)&1
+  timecode[7] = (ts['minute']>>1)&1
+  timecode[8] = ts['minute']&1
+  # populate hour
+  timecode[12] = (ts['hour']>>5)&1
+  timecode[13] = (ts['hour']>>4)&1
+  timecode[15] = (ts['hour']>>3)&1
+  timecode[16] = (ts['hour']>>2)&1
+  timecode[17] = (ts['hour']>>1)&1
+  timecode[18] = ts['hour']&1
+  # populate day number
+  timecode[22] = (ts['yday']>>9)&1
+  timecode[23] = (ts['yday']>>8)&1
+  timecode[25] = (ts['yday']>>7)&1
+  timecode[26] = (ts['yday']>>6)&1
+  timecode[27] = (ts['yday']>>5)&1
+  timecode[28] = (ts['yday']>>4)&1
+  timecode[30] = (ts['yday']>>3)&1
+  timecode[31] = (ts['yday']>>2)&1
+  timecode[32] = (ts['yday']>>1)&1
+  timecode[33] = ts['yday']&1
+  # populate parity bits
+  timecode[36] = calc_parity(ts['hour'])
+  timecode[37] = calc_parity(ts['minute'])
+  # populate year
+  timecode[41] = (ts['year']>>7)&1
+  timecode[42] = (ts['year']>>6)&1
+  timecode[43] = (ts['year']>>5)&1
+  timecode[44] = (ts['year']>>4)&1
+  timecode[45] = (ts['year']>>3)&1
+  timecode[46] = (ts['year']>>2)&1
+  timecode[47] = (ts['year']>>1)&1
+  timecode[48] = ts['year']&1
+  # populate day of the week
+  timecode[50] = (ts['wday']>>2)&1
+  timecode[51] = (ts['wday']>>1)&1
+  timecode[52] = ts['wday']&1
+  return timecode
+
+# generate an audio data chunk of specified duration
+def gen_audio(duration, freq=OP_FREQ, sr=48000):
+  smps = int(sr * duration)
+  # create the sine wave array for the whole second
+  rawdata = []
+  for k in range(0, sr):
+    v = math.sin(2 * math.pi * k * freq / sr)
+    if k > smps: # reduced power mode
+      v *= 0.1
+    rawdata.append(int(v * 32767)) # max gain
+  return array.array('h', rawdata).tobytes()
+
+# global buffers for audio data and current position
+curstream = b''
+streampos = 0
+
+# bitcode transmission callback
+def bitcode_transmit(in_data, frame_count, time_info, status):
+  global curstream, streampos
+  framelen = frame_count << 1 # 2 bytes per frame as we're using int16
+  framedata = curstream[streampos:streampos+framelen]
+  streampos += framelen
+  return (framedata, pyaudio.paContinue)
+
+# main logic is here
+def start_transmission(timeparams):
+  global curstream
+  p = pyaudio.PyAudio()
+  sr = timeparams['sr']
+  mins = timeparams['duration']
+  jjy_bit_chunks = [ # pregenerate the chunks
+    gen_audio(0.8, OP_FREQ, sr), # data bit 0
+    gen_audio(0.5, OP_FREQ, sr), # data bit 1
+    gen_audio(0.2, OP_FREQ, sr)  # marker bit
+  ]
+  ts = fetchtime(timeparams) # get the current timestamp
+  print('Time fetched (Unix):', ts['unix'])
+  bitcode = gentimecode(ts)[ts['second']+1:] # slice the rest of current minute
+  nextmin = ts['unix'] - ts['second'] # rewind to start of the minute
+  for i in range(0, mins): # generate bitcode for the next N minutes
+    nextmin += 60 # calc the next minute
+    bitcode += gentimecode(intreptime(nextmin))
+  print("Transmitting... Press Ctrl+C to exit")
+  # wait for the next second to start (roughly, with all the call overhead)
+  time.sleep((1 - datetime.datetime.now().microsecond/1000000)/2)
+  # open a PyAudio stream with callback
+  stream = p.open(format=pyaudio.paInt16, channels=1, frames_per_buffer=16384,
+            rate=sr, output=True, stream_callback=bitcode_transmit)
+  curstream = jjy_bit_chunks[bitcode.pop(0)] # preload the first second
+  while stream.is_active(): # wait for the stream to finish
+    if len(bitcode) > 0: # feed the stream in parallel
+      curstream += jjy_bit_chunks[bitcode.pop(0)]
+    time.sleep(0.75) # feeding the stream should be faster than realtime
+  # close audio
+  stream.stop_stream()
+  stream.close()
+  p.terminate()
+  print("Transmission ended")
+
+if __name__ == '__main__':
+  from argparse import ArgumentParser
+  parser = ArgumentParser(description='JJY.py: an opensource longwave time synchronizer for JJY40-enabled watches and clocks', epilog='(c) Luxferre 2024 --- No rights reserved <https://unlicense.org>')
+  parser.add_argument('-t', '--duration', type=int, default=30, help='Transmission duration (in minutes, default 30)')
+  parser.add_argument('-d', '--delta', type=int, default=0, help='Manual delta correction (in ms, must be determined individually, 0 by default)')
+  parser.add_argument('-o', '--tz-offset', type=float, default=9, help='Timezone offset from UTC to transmit (in hours, default 9 - corresponds to JST)')
+  parser.add_argument('-r', '--sample-rate', type=int, default=48000, help='Transmission sampling rate (in Hz, default 48000)')
+  parser.add_argument('-s', '--ntp-server', type=str, default=None, help='NTP server to sync from (if not specified then will sync from the local system time)')
+  parser.add_argument('-n', '--ntp-version', type=int, default=4, help='NTP protocol version to use (default 4)')
+  args = parser.parse_args()
+  params = { # populate parameters from the command line
+    'server': args.ntp_server, 'version': args.ntp_version,
+    'delta': args.delta, 'offset': int(args.tz_offset * 3600),
+    'sr': args.sample_rate, 'duration': args.duration
+  }
+  start_transmission(params)

requirements.txt

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+pyaudio>=0.2.14
+ntplib>=0.4.0