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@iPAS iPAS/cayennelpp.js
Last active Jan 21, 2020

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Cayenne Low-power Payload Decoder (javascript / node.js)
/**
* Cayenne Low-power Payload Library
*
* @author Pasakorn Tiwatthanont
* @email ptiwatthanont@gmail.com
*
* @link https://htmlcheatsheet.com/js/
*/
// console.log('Node.js version: ' + process.version)
format = require('string-format')
/**
* Byte stream to fixed-point decimal word.
*
* @param stream: array of bytes.
* @return: word of the bytes in big-endian format.
*/
function arrayToDecimal(stream, is_signed=false, decimal_point=0) {
var value = 0;
for (var i = 0; i < stream.length; i++) {
if (stream[i] > 0xFF)
throw 'Byte value overflow!';
value = (value<<8) | stream[i];
}
if (is_signed) {
edge = 1 << (stream.length )*8; // 0x1000..
max = (edge-1) >> 1; // 0x0FFF.. >> 1
value = (value > max) ? value - edge : value;
}
if (decimal_point) {
value /= Math.pow(10, decimal_point);
}
return value;
}
/**
* Cayenne Low-power Payload Decoder
*
* @param payload: array of bytes.
* @return: JSON
*/
function decode(payload) {
if (payload == null)
payload = [
0x01, 0x67, 0x00, 0xE1, // "temperature_1" : 22.5 (fixed point)
0x02, 0x73, 0x29, 0xEC, // "barometric_pressure_2": 1073.2 (fixed point)
0x03, 0x88, // "gps_3":
0x02, 0xDD, 0xFC, // { "latitude" : 18.79,
0x0F, 0x1A, 0x68, // "longitude": 98.98,
0x00, 0x79, 0x18, // "altitude" : 310 }
]
/**
* @reference https://github.com/myDevicesIoT/cayenne-docs/blob/master/docs/LORA.md
*
* Type IPSO LPP Hex Data Size Data Resolution per bit
* Digital Input 3200 0 0 1 1
* Digital Output 3201 1 1 1 1
* Analog Input 3202 2 2 2 0.01 Signed
* Analog Output 3203 3 3 2 0.01 Signed
* Illuminance Sensor 3301 101 65 2 1 Lux Unsigned MSB
* Presence Sensor 3302 102 66 1 1
* Temperature Sensor 3303 103 67 2 0.1 °C Signed MSB
* Humidity Sensor 3304 104 68 1 0.5 % Unsigned
* Accelerometer 3313 113 71 6 0.001 G Signed MSB per axis
* Barometer 3315 115 73 2 0.1 hPa Unsigned MSB
* Gyrometer 3334 134 86 6 0.01 °/s Signed MSB per axis
* GPS Location 3336 136 88 9 Latitude : 0.0001 ° Signed MSB
* Longitude : 0.0001 ° Signed MSB
* Altitude : 0.01 meter Signed MSB
*/
var sensor_types = {
0 : {'size': 1, 'name': 'Digital Input' , 'signed': false, 'decimal_point': 0,},
1 : {'size': 1, 'name': 'Digital Output' , 'signed': false, 'decimal_point': 0,},
2 : {'size': 2, 'name': 'Analog Input' , 'signed': true , 'decimal_point': 2,},
3 : {'size': 2, 'name': 'Analog Output' , 'signed': true , 'decimal_point': 2,},
101: {'size': 2, 'name': 'Illuminance Sensor' , 'signed': false, 'decimal_point': 0,},
102: {'size': 1, 'name': 'Presence Sensor' , 'signed': false, 'decimal_point': 0,},
103: {'size': 2, 'name': 'Temperature Sensor' , 'signed': true , 'decimal_point': 1,},
104: {'size': 1, 'name': 'Humidity Sensor' , 'signed': false, 'decimal_point': 1,},
113: {'size': 6, 'name': 'Accelerometer' , 'signed': true , 'decimal_point': 3,},
115: {'size': 2, 'name': 'Barometer' , 'signed': false, 'decimal_point': 1,},
134: {'size': 6, 'name': 'Gyrometer' , 'signed': true , 'decimal_point': 2,},
136: {'size': 9, 'name': 'GPS Location' , 'signed': false, 'decimal_point': [4,4,2], },};
var sensors = {};
var i = 0;
while (i < payload.length) {
// console.log(i);
// console.log(typeof payload[i])
// console.log(payload[i].toString())
s_no = payload[i++];
s_type = payload[i++];
if (typeof sensor_types[s_type] == 'undefined')
throw format('Sensor type error!: {}', s_type);
s_size = sensor_types[s_type].size;
s_name = sensor_types[s_type].name;
switch (s_type) {
case 0 : // Digital Input
case 1 : // Digital Output
case 2 : // Analog Input
case 3 : // Analog Output
case 101: // Illuminance Sensor
case 102: // Presence Sensor
case 103: // Temperature Sensor
case 104: // Humidity Sensor
case 113: // Accelerometer
case 115: // Barometer
case 134: // Gyrometer
s_value = arrayToDecimal(payload.slice(i, i+s_size),
is_signed = sensor_types[s_type].signed,
decimal_point = sensor_types[s_type].decimal_point);
//console.log(format('no:{} size:{} type:{} value:{}', s_no, s_size, s_name, s_value));
break;
case 136: // GPS Location
s_value = {
'latitude': arrayToDecimal(payload.slice(i+0, i+3), is_signed=sensor_types[s_type].signed, decimal_point=sensor_types[s_type].decimal_point[0]),
'longitude': arrayToDecimal(payload.slice(i+3, i+6), is_signed=sensor_types[s_type].signed, decimal_point=sensor_types[s_type].decimal_point[1]),
'altitude': arrayToDecimal(payload.slice(i+6, i+9), is_signed=sensor_types[s_type].signed, decimal_point=sensor_types[s_type].decimal_point[2]),};
//console.log(format('no:{} size:{} type:{} lat:{} lon:{} alt:{}', s_no, s_size, s_name, s_value.lat, s_value.lon, s_value.alt));
break;
}
sensors[s_no] = {'type': s_type, 'type_name': s_name, 'value': s_value };
i += s_size;
}
return sensors;
}
/**
* Test
*/
function test() {
// Test arrayToDecimal()
arrTest = [ 0xFF ];
console.log(arrayToDecimal(arrTest) + ' -> ' + arrayToDecimal(arrTest, is_signed=true)); // -1
arrTest = [ 0xFF, 0xFF ];
console.log(arrayToDecimal(arrTest) + ' -> ' + arrayToDecimal(arrTest, is_signed=true)); // -1
// Test decode()
console.log(decode());
}
test()
@hjmhardsoft

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hjmhardsoft commented Jan 20, 2020

The script decode Humidity incorrectly, due resolution for humidity is 0,5% per bit and no 0,1% per bit.
So, the code need to be modified, replacing

case 134: // Gyrometer
s_value = arrayToDecimal(payload.slice(i, i+s_size),
is_signed = sensor_types[s_type].signed,
decimal_point = sensor_types[s_type].decimal_point);
//console.log(format('no:{} size:{} type:{} value:{}', s_no, s_size, s_name, s_value));
break;

with

case 134: // Gyrometer
s_value = arrayToDecimal(payload.slice(i, i+s_size),
is_signed = sensor_types[s_type].signed,
decimal_point = sensor_types[s_type].decimal_point);
//console.log(format('no:{} size:{} type:{} value:{}', s_no, s_size, s_name, s_value));
if (s_type == 104) { s_value = s_value * 5}; // Humidity Data Resolution is 0,5% per bit, not 0,1% per bit
break;

@avbentem

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avbentem commented Jan 21, 2020

Alternatively, rather than adding a single exception, one could also replace the decimals handling. Like maybe make arrayToDecimal use some resolution parameter, rather than decimal_point:

function arrayToDecimal(stream, is_signed = false, resolution = 1) {
  ...
  value *= resolution;
  // Ensure the JavaScript IEEE 754 floating point calculations don't
  // return too many decimals, like for 111 * 0.1 = 11.100000000000001.
  // Unary plus-operator to cast string result of toFixed to number.
  return +value.toFixed(10);
}

...along with fixing all definitions to match the table from the comments:

  var sensor_types = {
    0: {size: 1, name: "Digital Input", signed: false, resolution: 1},
    1: {size: 1, name: "Digital Output", signed: false, resolution: 1},
    2: {size: 2, name: "Analog Input", signed: true, resolution: 0.01}
    ...
    104: {size: 1, name: "humidity", signed: false, resolution: 0.5},
    ...

...and the invocations, such as:

  while (i < payload.length) {
    ...
    switch (s_type) {
      ...
      case 104:  // Humidity Sensor
      case 113:  // Accelerometer
      case 115: // Barometer
      case 134: // Gyrometer
        s_value = arrayToDecimal(
          payload.slice(i, i + s_size),
          sensor_types[s_type].signed,
          sensor_types[s_type].resolution
        );
        break;
  ...

As for the additional use of toFixed, beware that JavaScript's 0.1 cannot be represented in an exact JavaScript IEEE 754 floating point, yielding funny results like 0.1 * 111= 11.100000000000001, while 111 / 10 = 11.1 and 0.01 * 111 = 1.11 are just fine.

Finally: lacking named parameters in JavaScript, using is_signed in is_signed = sensor_types[s_type].signed really just creates a temporary variable that is not used anywhere in the code, so can be omitted.

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