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October 25, 2019 23:53
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https://github.com/ERNICommunity/hnh19ech-iot sends 2 bytes to TTN: temperature [ °C ], byte[0]: integer part, byte[1]: fraction (1/100 °C)
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var bytesToInt = function(bytes) { | |
var i = 0; | |
for (var x = 0; x < bytes.length; x++) { | |
i |= +(bytes[x] << (x * 8)); | |
} | |
return i; | |
}; | |
var unixtime = function(bytes) { | |
if (bytes.length !== unixtime.BYTES) { | |
throw new Error('Unix time must have exactly 4 bytes'); | |
} | |
return bytesToInt(bytes); | |
}; | |
unixtime.BYTES = 4; | |
var uint8 = function(bytes) { | |
if (bytes.length !== uint8.BYTES) { | |
throw new Error('int must have exactly 1 byte'); | |
} | |
return bytesToInt(bytes); | |
}; | |
uint8.BYTES = 1; | |
var uint16 = function(bytes) { | |
if (bytes.length !== uint16.BYTES) { | |
throw new Error('int must have exactly 2 bytes'); | |
} | |
return bytesToInt(bytes); | |
}; | |
uint16.BYTES = 2; | |
var latLng = function(bytes) { | |
if (bytes.length !== latLng.BYTES) { | |
throw new Error('Lat/Long must have exactly 8 bytes'); | |
} | |
var lat = bytesToInt(bytes.slice(0, latLng.BYTES / 2)); | |
var lng = bytesToInt(bytes.slice(latLng.BYTES / 2, latLng.BYTES)); | |
return [lat / 1e6, lng / 1e6]; | |
}; | |
latLng.BYTES = 8; | |
var temperature = function(bytes) { | |
if (bytes.length !== temperature.BYTES) { | |
throw new Error('Temperature must have exactly 2 bytes'); | |
} | |
var isNegative = bytes[0] & 0x80; | |
var b = ('00000000' + Number(bytes[0]).toString(2)).slice(-8) | |
+ ('00000000' + Number(bytes[1]).toString(2)).slice(-8); | |
if (isNegative) { | |
var arr = b.split('').map(function(x) { return !Number(x); }); | |
for (var i = arr.length - 1; i > 0; i--) { | |
arr[i] = !arr[i]; | |
if (arr[i]) { | |
break; | |
} | |
} | |
b = arr.map(Number).join(''); | |
} | |
var t = parseInt(b, 2); | |
if (isNegative) { | |
t = -t; | |
} | |
return t / 1e2; | |
}; | |
temperature.BYTES = 2; | |
var humidity = function(bytes) { | |
if (bytes.length !== humidity.BYTES) { | |
throw new Error('Humidity must have exactly 2 bytes'); | |
} | |
var h = bytesToInt(bytes); | |
return h / 1e2; | |
}; | |
humidity.BYTES = 2; | |
var bitmap = function(byte) { | |
if (byte.length !== bitmap.BYTES) { | |
throw new Error('Bitmap must have exactly 1 byte'); | |
} | |
var i = bytesToInt(byte); | |
var bm = ('00000000' + Number(i).toString(2)).substr(-8).split('').map(Number).map(Boolean); | |
return ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] | |
.reduce(function(obj, pos, index) { | |
obj[pos] = bm[index]; | |
return obj; | |
}, {}); | |
}; | |
bitmap.BYTES = 1; | |
var decode = function(bytes, mask, names) { | |
var maskLength = mask.reduce(function(prev, cur) { | |
return prev + cur.BYTES; | |
}, 0); | |
if (bytes.length < maskLength) { | |
throw new Error('Mask length is ' + maskLength + ' whereas input is ' + bytes.length); | |
} | |
names = names || []; | |
var offset = 0; | |
return mask | |
.map(function(decodeFn) { | |
var current = bytes.slice(offset, offset += decodeFn.BYTES); | |
return decodeFn(current); | |
}) | |
.reduce(function(prev, cur, idx) { | |
prev[names[idx] || idx] = cur; | |
return prev; | |
}, {}); | |
}; | |
if (typeof module === 'object' && typeof module.exports !== 'undefined') { | |
module.exports = { | |
unixtime: unixtime, | |
uint8: uint8, | |
uint16: uint16, | |
temperature: temperature, | |
humidity: humidity, | |
latLng: latLng, | |
bitmap: bitmap, | |
decode: decode | |
}; | |
} | |
function Decoder(bytes, port) { | |
// Define the order in which the fields are sent, and their | |
// names in the JSON output | |
return decode(bytes, | |
[temperature, humidity], | |
['temp [°C]', 'humidity [%]']); | |
} |
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