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JJY.js: Web Audio API based JJY transmitter

JJY.js: JJY time signal emulation/transmission library

Usage

  1. Make sure that the watch/clock is configured to receive JJY 40 KHz signal (for most Casio Waveceptor/G-Shock watches, the easiest way is to enter the engineer menu by pressing Mode+Light+Receive and select J 40 reception mode, for all other watches you need to set the home city to Tokyo)
  2. Make sure your device clock is in sync before running the emulator.
  3. From the page, run:
var jjy = JJY()
jjy.run()

The library automatically transcodes your local time into Japanese timezone regardless which timezone you're in.

To transmit a single timecode (Date object must be constructed in UTC) steadily: jjy.run(DateObject)

To change the waveform distortion parameter (for debug/wave experiment purposes), pass a numeric float value above 2 to JJY constructor (default is equal to 1/3 of current AudioContext sampling rate).

  1. Start the reception and place the watch/clock close to device speaker or headphones.

Demo

A functional demo (with explanations of internal workings) of JJY.js is available at Fukushima web page.

/*
JJY.js: JJY time signal emulation/transmission library
Copyright (c) @plugnburn (831337.xyz) 2017
@license ISC
*/
function JJY(distorter) { //JJY constructor
distorter = parseFloat(distorter)
//create pre-filled constant array for efficient copying
var codeProto = '200000000200000000020000000002000000000200000000020000000002'.split('').map(Number)
function toBCD(val) {
return val%10 + (((val/10)%10)<<4) + ((val/100)<<8)
}
function calcParity(val){
var i = 0;
while(val) {
i ^= val & 1
val >>>= 1
}
return i
}
function jjyTimecode(timeObj) { //generate a JJY timecode from any given Date object
var ts = {
min: toBCD(timeObj.getUTCMinutes()),
hour: toBCD(timeObj.getUTCHours()),
day: toBCD(Math.floor((timeObj - new Date(timeObj.getUTCFullYear(),0,0,0,0))/864e5)),
year: toBCD(timeObj.getUTCFullYear() % 100),
weekDay: timeObj.getUTCDay()
}, timeCode = codeProto.slice();
//populate minute
timeCode[1] = (ts.min>>6)&1
timeCode[2] = (ts.min>>5)&1
timeCode[3] = (ts.min>>4)&1
timeCode[5] = (ts.min>>3)&1
timeCode[6] = (ts.min>>2)&1
timeCode[7] = (ts.min>>1)&1
timeCode[8] = ts.min&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.day>>9)&1
timeCode[23] = (ts.day>>8)&1
timeCode[25] = (ts.day>>7)&1
timeCode[26] = (ts.day>>6)&1
timeCode[27] = (ts.day>>5)&1
timeCode[28] = (ts.day>>4)&1
timeCode[30] = (ts.day>>3)&1
timeCode[31] = (ts.day>>2)&1
timeCode[32] = (ts.day>>1)&1
timeCode[33] = ts.day&1
//populate parity bits
timeCode[36] = calcParity(ts.hour)
timeCode[37] = calcParity(ts.min)
//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.weekDay>>2
timeCode[51] = (ts.weekDay>>1)&1
timeCode[52] = ts.weekDay&1
return timeCode
}
function getJJYTimeCode(timeObj) {
var timeRep = timeObj || new Date(Date.now() + 324e5);
return {
bitCode: jjyTimecode(timeRep),
cs: timeRep.getUTCSeconds()
}
}
return {
getTimeCode: getJJYTimeCode, //exposed for getting timecode information in non-browser environments
run: function(tObj) { //browser-only function, requires Web Audio API support
var ctx = new (window.AudioContext || window.webkitAudioContext)(),
sr = ctx.sampleRate,
opFreq = 40000/3,
rp = opFreq/sr, bufSet = [], pwm = [.8, .5, .2];
if(isNaN(distorter) || distorter < 2)
distorter = sr/3
ctx.createBuffer = ctx.createBuffer || ctx.webkitCreateBuffer;
ctx.createBufferSource = ctx.createBufferSource || ctx.webkitCreateBufferSource;
performance.now = performance.now || performance.webkitNow || function(){return (new Date).getTime()}
secondTick = (function(tm){
var px = 0, py = 0, dx = 0;
return function(cb){
px = performance.now()
setTimeout(function(){
dx = (py = performance.now()) - px - tm
px = py
cb()
}, tm - dx/2)
}
})(1000)
// pre-populate the buffers
for(var i=0;i<3;i++) {
var sLen = sr*pwm[i];
bufSet[i] = ctx.createBuffer(1, sLen, sr);
var cData = bufSet[i].getChannelData(0);
for(var k=0;k<sLen;k++)
cData[k] = Math.floor(distorter*Math.sin(2 * Math.PI * k * rp))/distorter
}
// play back the timecode
var renderMinute = function() {
var sigInfo = getJJYTimeCode(tObj), currentIndex = sigInfo.cs,
renderSecond = function() {
secondTick(currentIndex<59 ? renderSecond : renderMinute)
var bs = ctx.createBufferSource()
bs.buffer = bufSet[sigInfo.bitCode[currentIndex]]
bs.connect(ctx.destination)
bs.start()
currentIndex++
}
renderSecond()
}
renderMinute()
}
}
}
if(typeof module !== 'undefined' && module.exports && this.module !== module)
module.exports = JJY()
@Mnkai

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Mnkai commented Jul 22, 2018

On the line 31, you may have intended
day: toBCD(Math.floor((timeObj - new Date(timeObj.getUTCFullYear(),0,1))/864e5)+1),
instead of current
day: toBCD(Math.floor((timeObj - new Date(timeObj.getUTCFullYear(),0,0,0,0))/864e5)),

JS Date object's month index starts from 0, and day index starts from 1. (I know, it's strange)

@plugnburn

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plugnburn commented May 30, 2019

On the line 31, you may have intended
day: toBCD(Math.floor((timeObj - new Date(timeObj.getUTCFullYear(),0,1))/864e5)+1),
instead of current
day: toBCD(Math.floor((timeObj - new Date(timeObj.getUTCFullYear(),0,0,0,0))/864e5)),

JS Date object's month index starts from 0, and day index starts from 1. (I know, it's strange)

Nope, that was intended, because of the way JJY timecode requires day representation.

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