Send modbus slave data via lorawan

[Gusti Made Arya Wijaya]

Hello,
I'm currently starting a project to read Modbus slave data and send it via lorawan to TTN. I combining lorawan with OTAA code with pycom_modbus code , here is my code

#!/usr/bin/env python
#
# Copyright (c) 2019, Pycom Limited.
#
# This software is licensed under the GNU GPL version 3 or any
# later version, with permitted additional terms. For more information
# see the Pycom Licence v1.0 document supplied with this file, or
# available at https://www.pycom.io/opensource/licensing
#
import pycom
from uModBus.serial import Serial
from uModBus.tcp import TCP
from network import WLAN
from network import LoRa
import socket
import machine
import ubinascii
import time


#pycom.pybytes_on_boot(False)

lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.AS923)

# create an OTAA authentication parameters, change them to the provided credentials
app_eui = ubinascii.unhexlify('70B3D57ED0037CB2')
app_key = ubinascii.unhexlify('6CE141489C7DA7312C0523697A7B2F30')

# join a network using OTAA (Over the Air Activation)
#uncomment below to use LoRaWAN application provided dev_eui
lora.join(activation=LoRa.OTAA, auth=(app_eui, app_key), timeout=0)
#lora.join(activation=LoRa.OTAA, auth=(dev_eui, app_eui, app_key), timeout=0)

# wait until the module has joined the network
while not lora.has_joined():
    time.sleep(2.5)
    print('Not yet joined...')

print('Joined')
# create a LoRa socket
s = socket.socket(socket.AF_LORA, socket.SOCK_RAW)

# set the LoRaWAN data rate
s.setsockopt(socket.SOL_LORA, socket.SO_DR, 5)

# make the socket blocking
# (waits for the data to be sent and for the 2 receive windows to expire)
s.setblocking(True)

######################### RTU SERIAL MODBUS #########################
uart_id = 0x01
#modbus_obj = Serial(uart_id, pins=('P3','P4')) #default p3 p4 ==> tx1 rx1
#modbus_obj = Serial(uart_id, pins=('P3','P4'), ctrl_pin='P8')
modbus_obj = Serial(uart_id, pins=('P10','P14'), ctrl_pin='P20') 

###################### READ HOLDING REGISTERS ##################
slave_addr=0x01
starting_address=0x25
register_quantity=2
signed=True

while True:
    #read modbus slave data_bit
    register_value = modbus_obj.read_holding_registers(slave_addr, starting_address, register_quantity, signed)
    #print('Holding register value: ' + ' '.join('{:#x}'.format(x) for x in register_value))

    # send some data
    #s.send(bytes([0x01, 0x02, 0x03]))
    s.send(register_value)

    # make the socket non-blocking
    # (because if there's no data received it will block forever...)
    s.setblocking(False)

    # get any data received (if any...)
    data = s.recv(64)
    #print(data)
    time.sleep(120)

I got an error message like this,

I don't know yet how to send the data, because I'm a newbie in python.

[Gusti Made Arya Wijaya]

@Gusti-Made-Arya-Wijaya I've fixed this problem, basically, data from Modbus Slave is byte HEX, so I think to not use conversion function in serial.py.
and here is the result, TTN receive HEX data from lopy4

Thanks all for the replies

[tuftec]

This works for me.
LoRaSock.send(bytes([0x01, 0x02])+pack('>h',nvvar['Level']&0xffff)+bytes([0x02, 0x02])+pack('>h',nvvar['Batt']&0xffff))

are my variables.

[Gusti Made Arya Wijaya]

@kjm I think for OTAA mode is no problem. the problem is how to convert the register value to byte

[Gusti Made Arya Wijaya]

@tuftec data type of register_value is a tuple with int value (17109, 20578), I've tried s.send(bytes(register_value)) but still error. I don't know how to convert the value to byte

[tuftec]

Not sure exactly what line corresponds to line 71, but I suspect it is the s.send(register_value) line.
I think you just need to change the type to bytes. Just try s.send(bytes(register_value)).

[kjm]

I have no luck with OTA mode on TTN for the lopy4, but ABP works OK