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Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

This article documents a change to the sensor configuration and payload formatter adding another temperature and humidity sensor for the greenhouse.

The sensors are now:

• ID=1 air temperature and humidity;
• ID=2 soil temperature and humidity.
• ID=3 greenhouse temperature and humidity.

The payload contains an 8bit payload version number then six 16bit values for the six sensors. This is parsed by the TTN uplink formatter.

RS485-LN firmware has been upgraded to v1.4.

Uplink formatter

function decodeUplink(input) {
  ab=new ArrayBuffer(input.bytes.length);
  const abv=new DataView(ab,0,ab.byteLength);
  for(var i=0;i<ab.byteLength;i++)abv.setUint8(i,input.bytes[i]);
  var payver=abv.getUint8(0);
  switch(payver){
    case 1:
      if(ab.byteLength<13){return {errors:["Bad payload length"]};}
      result={
        data:{
            field1:abv.getInt16(3)/10,
            field2:abv.getInt16(1)/10,
            field3:abv.getInt16(7)/10,
            field4:abv.getInt16(5)/10,
            field5:abv.getInt16(11)/10,
            field6:abv.getInt16(9)/10
        },
      warnings:[], // optional
      errors:[] // optional (if set, the decoding failed)
      };
      if(result.data.field2===-1){result.data.field1=null;result.data.field2=null}
      if(result.data.field4===-1){result.data.field3=null;result.data.field4=null}
      if(result.data.field6===-1){result.data.field5=null;result.data.field6=null}
      return result;
    default:
      return {errors:["Unknown payver"]};
    }
  }

Above, is the Custom Javascript formatter which writes the measured values into variables fields1-field6 of the data object.

This formatter is for firmware v1.4 which simply returns all ones in fields for MODBUS devices that do not respond with valid data. In this case, the humidity fields should never be -1, so they are used as a test for data valid.

This is not a good general solution. I suggested the following to Dragino:

A possible solution is to add a 16 bit field to the payload with a bit for each AT+COMMANDn to indicate that a valid response was received to that command (ie did not time out waiting for response, good CRC decoded). I could test those bits in the javascript uplink formatter, and supply null if the data was not valid.

This approach would be backwards compatible with v1.03 as it is an additional 16 bit field at the end of the payload, code reading v1.03 payloads would simply ignore the extra two bytes.

RS485-LN configuration

See the earlier articles in the series for details of the serial port client and configuration.

123456
AT+DEBUG
AT+BAUDR=4800
AT+DATAUP=0
AT+PAYVER=1
AT+DATACUT1=0,0,0
AT+DATACUT2=0,0,0
AT+DATACUT3=0,0,0 
AT+MBFUN=1
AT+COMMAND1=01 04 00 00 00 02,1
AT+COMMAND2=02 04 00 00 00 02,1
AT+COMMAND3=03 04 00 00 00 02,1
AT+CMDDL1=200
AT+CMDDL2=200
AT+CMDDL3=200

Above, the script sends the password (which if already unlocked will cause an error which can be ignored) and commands to configure sampling of the two sensors, and packaging of the results in the payload.

Configure Thingspeak channel for the six data fields

The six data fields were displayed in a new channel on Thingspeak.

Write and test Thingspeak webhook

This task is simply collecting the URL and access credentials for write access to the Thingspeak channel.

Above is a capture over some days. The zero glitch in the greenhouse sensor has been addressed by increasing timeout, and revision of the uplink formatter to discard invalid data.

Air time

At this time, the gateway is very close to the RS485-LN, and DR5 (SF7 BW125kHz) is selected by ADR.

Above is a calculation using Semtech’s calculator.

Above is a screenshot from Airtime calculator for LoRaWAN. In checking the Radiocommunications (Low Interference Potential Devices) Class Licence 2015 as ammended 05/03/2022 (latest at time of writing), there is no limitation on dwell time in Australia under that licence. That said, the downloaded MAC data for the device includes “uplink_dwell_time”: true.

To be continued…

Links / references

• Garden environmental telemetry project – part 4
• Garden environmental telemetry project – part 3
• Garden environmental telemetry project – part 2
• Garden environmental telemetry project – part 1

Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

This article documents a change to the sensor configuration and payload formatter in preparation for another RS485-LN.

The sensors are now:

• ID=1 air temperature and humidity;
• ID=2 soil temperature and humidity.

The payload  contains a 8bit payload version number then four 16bit values for the four sensors. This is parsed by the TNN uplink formatter.

function decodeUplink(input) {
  var payver=input.bytes[0];
  switch(payver){
    case 1:
      return {
        data: {
          field3: ((input.bytes[3]<< 8)|input.bytes[4])/10,
          field4: ((input.bytes[1]<< 8)|input.bytes[2])/10,
          field5: ((input.bytes[7]<< 8)|input.bytes[8])/10,
          field6: ((input.bytes[5]<< 8)|input.bytes[6])/10
        },
      warnings: [], // optional
      errors: [] // optional (if set, the decoding failed)
      };
    case 2:
      break;
    }
  }

Above, is the Custom Javascript formatter which writes the measured values into variables fields3-field6 of the data object.

To be continued…