Reading PZEM-004t power sensor (new version v3.0) through Modbus-RTU protocol over TTL UART

pzem_004t.py

# Reading PZEM-004t power sensor (new version v3.0) through Modbus-RTU protocol over TTL UART
# Run as:
# python3 pzem_004t.py

# To install dependencies: 
# pip install modbus-tk
# pip install pyserial

import serial
import modbus_tk.defines as cst
from modbus_tk import modbus_rtu

# Connect to the sensor
sensor = serial.Serial(
    port='/dev/PZEM_sensor',
    baudrate=9600,
    bytesize=8,
    parity='N',
    stopbits=1,
    xonxoff=0
)

master = modbus_rtu.RtuMaster(sensor)
master.set_timeout(2.0)
master.set_verbose(True)

data = master.execute(1, cst.READ_INPUT_REGISTERS, 0, 10)

voltage = data[0] / 10.0 # [V]
current = (data[1] + (data[2] << 16)) / 1000.0 # [A]
power = (data[3] + (data[4] << 16)) / 10.0 # [W]
energy = data[5] + (data[6] << 16) # [Wh]
frequency = data[7] / 10.0 # [Hz]
powerFactor = data[8] / 100.0
alarm = data[9] # 0 = no alarm

print('Voltage [V]: ', voltage)
print('Current [A]: ', current)
print('Power [W]: ', power) # active power (V * I * power factor)
print('Energy [Wh]: ', energy)
print('Frequency [Hz]: ', frequency)
print('Power factor []: ', powerFactor)
print('Alarm : ', alarm)

# Changing power alarm value to 100 W
# master.execute(1, cst.WRITE_SINGLE_REGISTER, 1, output_value=100)

try:
    master.close()
    if sensor.is_open:
        sensor.close()
except:
    pass

this only print the data once right and not a loop? what does the .close() method do?

this only print the data once right and not a loop?

Hi, @FujiwaraKengo . That is correct, data is printed out only once and then the scripts ends, closing the communication channel. You could put the reading part in a loop (lines 27 to 43), allowing for a reasonable waiting time between iterations, or call the full script periodically.

Can this script be modified for usage with Windows? Changing "/dev/PZEM_sensor" to the comport of the FTDI-cable results in

Traceback (most recent call last):
  File "g:\PZEM-004T\pzem_004t.py", line 27, in <module>
    data = master.execute(1, cst.READ_INPUT_REGISTERS, 0, 10)
  File "c:\Users\Bart\AppData\Local\Programs\Python\Python310\lib\site-packages\modbus_tk\utils.py", line 39, in new
    raise excpt
  File "c:\Users\Bart\AppData\Local\Programs\Python\Python310\lib\site-packages\modbus_tk\utils.py", line 37, in new
    ret = fcn(*args, **kwargs)
  File "c:\Users\Bart\AppData\Local\Programs\Python\Python310\lib\site-packages\modbus_tk\modbus.py", line 356, in execute
    response_pdu = query.parse_response(response)
  File "c:\Users\Bart\AppData\Local\Programs\Python\Python310\lib\site-packages\modbus_tk\modbus_rtu.py", line 46, in parse_response
    raise ModbusInvalidResponseError("Response length is invalid {0}".format(len(response)))
modbus_tk.exceptions.ModbusInvalidResponseError: Response length is invalid 0

Yes, I checked the Tx-/Rx-connections.

edit: Hmm, seems it does this when there are no readings (didn't connect AC-side), I am getting output when AC-side is connected. So I added an try/except for modbus_rtu.ModbusInvalidResponseError and an if-statement to check if data contains something.

Now to figure out how to change the address from Python.
edit: data = master.execute(1, cst.WRITE_SINGLE_REGISTER, 2, output_value=2)
seems to do that :)