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random-signal

Generate a pseudo-random signal for mocking Sensor data

var RandomSignal = require("../.")

var opt = {
  sep: "\n"     // seperator
, tdelta: 200   // milliseconds
}

var rs = RandomSignal(opt)

rs.pipe(process.stdout)

setTimeout( function () {
  rs.destroy()
}, 1000)

outputs

{"x":"2014-02-26 16:30:57.918","y":1.3151883383869654}
{"x":"2014-02-26 16:30:58.123","y":4.24176480313184}
{"x":"2014-02-26 16:30:58.328","y":3.719194025237043}
{"x":"2014-02-26 16:30:58.529","y":3.7442073803567077}

Options

Along with Readable stream options, (including object mode) you may pass in these options or use the defaults given below

  var tdelta = opt.tdelta || 50
    , hz = opt.hz || (1 / 20 * tdelta)
    , amp = opt.amp || 1
    , noiseHz = opt.noiseHz || 4 * hz
    , noiseAmp = opt.noiseAmp || 0.3 * amp
    , trendIV = opt.trendIV || (1000 * 1/hz)
    , lowtrend = opt.lowtrend || -amp
    , hightrend = opt.hightrend || amp
    , sep = opt.sep || ""
    , timeFormatter = opt.timeFormatter || getTimeString

where

y = amp * Math.sin(hz*ts) + noise + trend
  = amp * Math.sin(hz*ts) + noise(0, noiseAmp) + Math.sin(noiseHz*ts) + trend
  = amp * Math.sin(hz*ts) + noise(0, noiseAmp) + Math.sin(noiseHz*ts) + noise(lowtrend, hightrend)

with

noise = function(low, high) {
  Math.random() * (low - high + 1) + low
}

tdelta (milliseconds)

The millisecond time that data will be produced. The default is 50ms.

hz (seconds)

The frequency of the underlying sine signal. The default frequency for the sine wave is 1 cycle per 20 tdelta's. This means that each cycle is fairly well sampled. It also means that setting tdelta = 50 will result in a default of a cycle per second.

amp

The amplitude of the underlying sine signal.

noizeHz (seconds)

The frequency of the applied noise signal

noiseAmp

The amplitude of the noise which will be randomly generated between 0 and noiseAmp

trendIV (milliseconds)

The millisecond interval in which to apply a random trend constant to the output data. The default is 1000 * 1/hz which provides a new trend every cycle of the underlying sine wave. If you want a longer trend, say applied every 5 cycles, set trendIV = 5000 * 1/hz. Remember the trendIV is in milliseconds, so the 1000 multiplication is necessary.

hightrend

The maximum amplitude of the randomly applied constant trend. The default is 1.

lowtrend

The minimum amplitude of the randomly applied constant trend. The default is -1.

sep

If the stream is not configured in objectMode this seperator will be applied to the end of the utf8 encoded string buffer. The default is set to empty string "".

timeFormatter

A function that takes a Javascript Date object as inputs and outputs a formatted date string. The default getTimeString function will output dates as "YYYY-MM-SS HH:MM:SS.f"

Install

npm install random-signal