TTN Smart Sensor (Mcci)

Codec Preview

/* Name: catena-message-port2-format-22-decoder-ttn.js Function: Decode port 0x02 format 0x22 messages for TTN console. Copyright and License: See accompanying LICENSE file at https://github.com/mcci-catena/MCCI-Catena-4430/ Author: Terry Moore, MCCI Corporation August 2019 */ // calculate dewpoint (degrees C) given temperature (C) and relative humidity (0..100) // from http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html // rearranged for efficiency and to deal sanely with very low (< 1%) RH function dewpoint(t, rh) { var c1 = 243.04; var c2 = 17.625; var h = rh / 100; if (h <= 0.01) h = 0.01; else if (h > 1.0) h = 1.0; var lnh = Math.log(h); var tpc1 = t + c1; var txc2 = t * c2; var txc2_tpc1 = txc2 / tpc1; var tdew = c1 * (lnh + txc2_tpc1) / (c2 - lnh - txc2_tpc1); return tdew; } /* Name: CalculateHeatIndex() Description: Calculate the NWS heat index given dry-bulb T and RH Definition: function CalculateHeatIndex(t, rh) -> value or null Description: T is a Farentheit temperature in [76,120]; rh is a relative humidity in [0,100]. The heat index is computed and returned; or an error is returned. For consistency with the other temperature, despite the heat index being defined in Farenheit, we return in Celsius. Returns: number => heat index in Farenheit. null => error. References: https://github.com/mcci-catena/heat-index/ https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml Results was checked against the full chart at iweathernet.com: https://www.iweathernet.com/wxnetcms/wp-content/uploads/2015/07/heat-index-chart-relative-humidity-2.png The MCCI-Catena heat-index site has a test js script to generate CSV to match the chart, a spreadsheet that recreates the chart, and a spreadsheet that compares results. */ function CalculateHeatIndex(t, rh) { var tRounded = Math.floor(t + 0.5); // return null outside the specified range of input parameters if (tRounded < 76 || tRounded > 126) return null; if (rh < 0 || rh > 100) return null; // according to the NWS, we try this first, and use it if we can var tHeatEasy = 0.5 * (t + 61.0 + ((t - 68.0) * 1.2) + (rh * 0.094)); // The NWS says we use tHeatEasy if (tHeatHeasy + t)/2 < 80.0 // This is the same computation: if ((tHeatEasy + t) < 160.0) return (tHeatEasy - 32) * 5 / 9; // need to use the hard form, and possibly adjust. var t2 = t * t; // t squared var rh2 = rh * rh; // rh squared var tResult = -42.379 + (2.04901523 * t) + (10.14333127 * rh) + (-0.22475541 * t * rh) + (-0.00683783 * t2) + (-0.05481717 * rh2) + (0.00122874 * t2 * rh) + (0.00085282 * t * rh2) + (-0.00000199 * t2 * rh2); // these adjustments come from the NWA page, and are needed to // match the reference table. var tAdjust; if (rh < 13.0 && 80.0 <= t && t <= 112.0) tAdjust = -((13.0 - rh) / 4.0) * Math.sqrt((17.0 - Math.abs(t - 95.0)) / 17.0); else if (rh > 85.0 && 80.0 <= t && t <= 87.0) tAdjust = ((rh - 85.0) / 10.0) * ((87.0 - t) / 5.0); else tAdjust = 0; // apply the adjustment tResult += tAdjust; // finally, the reference tables have no data above 183 (rounded), // so filter out answers that we have no way to vouch for. if (tResult >= 183.5) return null; else return (tResult - 32) * 5 / 9; } function DecodeU16(Parse) { var i = Parse.i; var bytes = Parse.bytes; var result = (bytes[i] << 8) + bytes[i + 1]; Parse.i = i + 2; return result; } function DecodeUflt16(Parse) { var rawUflt16 = DecodeU16(Parse); var exp1 = rawUflt16 >> 12; var mant1 = (rawUflt16 & 0xFFF) / 4096.0; var f_unscaled = mant1 * Math.pow(2, exp1 - 15); return f_unscaled; } function DecodeSflt16(Parse) { var rawSflt16 = DecodeU16(Parse); // rawSflt16 is the 2-byte number decoded from wherever; // it's in range 0..0xFFFF // bit 15 is the sign bit // bits 14..11 are the exponent // bits 10..0 are the the mantissa. Unlike IEEE format, // the msb is explicit; this means that numbers // might not be normalized, but makes coding for // underflow easier. // As with IEEE format, negative zero is possible, so // we special-case that in hopes that JavaScript will // also cooperate. // // The result is a number in the open interval (-1.0, 1.0); // // throw away high bits for repeatability. rawSflt16 &= 0xFFFF; // special case minus zero: if (rawSflt16 === 0x8000) return -0.0; // extract the sign. var sSign = ((rawSflt16 & 0x8000) !== 0) ? -1 : 1; // extract the exponent var exp1 = (rawSflt16 >> 11) & 0xF; // extract the "mantissa" (the fractional part) var mant1 = (rawSflt16 & 0x7FF) / 2048.0; // convert back to a floating point number. We hope // that Math.pow(2, k) is handled efficiently by // the JS interpreter! If this is time critical code, // you can replace by a suitable shift and divide. var f_unscaled = sSign * mant1 * Math.pow(2, exp1 - 15); return f_unscaled; } function DecodeLight(Parse) { return DecodeUflt16(Parse); } function DecodeActivity(Parse) { return DecodeSflt16(Parse); } function DecodeI16(Parse) { var i = Parse.i; var bytes = Parse.bytes; var result = (bytes[i] << 8) + bytes[i + 1]; Parse.i = i + 2; // interpret uint16 as an int16 instead. if (result & 0x8000) result += -0x10000; return result; } function DecodeI32(Parse) { var i = Parse.i; var bytes = Parse.bytes; var result = (bytes[i + 0] << 24)+ (bytes[i + 1] << 16) + (bytes[i + 2] << 8) + bytes[i + 3]; Parse.i = i + 4; // interpret uint16 as an int16 instead. if (result & 0x80000000) result += -0x100000000; return result; } function DecodeU32(Parse) { var i = Parse.i; var bytes = Parse.bytes; var result = (bytes[i + 0] << 24)+ (bytes[i + 1] << 16) + (bytes[i + 2] << 8) + bytes[i + 3]; Parse.i = i + 4; return result; } function RemainingBytes(Parse) { var i = Parse.i; var nBytes = Parse.bytes.length; if (i < nBytes) return (nBytes - i); else return 0; } function DecodeV(Parse) { return DecodeI16(Parse) / 4096.0; } function Decoder(bytes, port) { // Decode an uplink message from a buffer // (array) of bytes to an object of fields. var decoded = {}; if (! (port === 2)) return null; var uFormat = bytes[0]; if (! (uFormat === 0x22)) return null; // an object to help us parse. var Parse = {}; Parse.bytes = bytes; // i is used as the index into the message. Start with the time. Parse.i = 1; // fetch time, convert from GPS to ISO time assuming 17 leap seconds, // and then convert to JSON format. decoded.time = new Date((DecodeU32(Parse) + 315964800 - 17) * 1000).toJSON(); // fetch the bitmap. var flags = bytes[Parse.i++]; if (flags & 0x1) { decoded.Vbat = DecodeV(Parse); } if (flags & 0x2) { decoded.Vsys = DecodeV(Parse); } if (flags & 0x4) { decoded.Vbus = DecodeV(Parse); } if (flags & 0x8) { var iBoot = bytes[Parse.i++]; decoded.boot = iBoot; } if (flags & 0x10) { // we have temp, pressure, RH decoded.tempC = DecodeI16(Parse) / 256; decoded.p = DecodeU16(Parse) * 4 / 100.0; decoded.rh = DecodeU16(Parse) * 100 / 65535.0; decoded.tDewC = dewpoint(decoded.tempC, decoded.rh); var tHeat = CalculateHeatIndex(decoded.tempC * 1.8 + 32, decoded.rh); if (tHeat !== null) decoded.tHeatIndexC = tHeat; } if (flags & 0x20) { // we have light decoded.irradiance = {}; decoded.irradiance.White = DecodeLight(Parse) * Math.pow(2.0, 24); } if (flags & 0x40) { // we have gpio counts decoded.pellets = []; for (var i = 0; i < 2; ++i) { decoded.pellets[i] = {}; decoded.pellets[i].Total = DecodeU16(Parse); decoded.pellets[i].Delta = bytes[Parse.i++]; } } if (flags & 0x80) { // we have Activity decoded.activity = []; var i = 0; while (RemainingBytes(Parse) >= 2) { decoded.activity[i] = DecodeActivity(Parse); ++i; } } return decoded; } // TTN V3 decoder function decodeUplink(tInput) { var decoded = Decoder(tInput.bytes, tInput.fPort); var result = {}; result.data = decoded; return result; }