Data acquisition

Pecos includes basic data acquisition methods to transfer data from sensors to an SQL database. These methods require the Python packages sqlalchemy ( and minimalmodbus (

Device to client

The device_to_client method collects data from a modbus device and stores it in a local MySQL database. The method requires several configuration options, which are stored as a nested dictionary. pyyaml can be used to store configuration options in a file. The options are stored in a Client block and a Devices block. The Devices block can define multiple devices and each device can have multiple data streams. The configuration options are described below.

  • Client: A dictionary that contains information about the client. The dictionary has the following keys:

    • IP: IP address (string)

    • Database: name of database (string)

    • Table: name of table (string)

    • Username: name of user (string)

    • Password: password for user (string)

    • Interval: data collection frequency in seconds (integer)

    • Retries: number of retries for each channel (integer)

  • Devices: A list of dictionaries that contain information about each device (one dictionary per device). Each dictionary has the following keys:

    • Name: modbus device name (string)

    • USB: serial connection (string) e.g. /dev/ttyUSB0 for linux

    • Address: modbus slave address (string)

    • Baud: data transfer rate in bits per second (integer)

    • Parity: parity of transmitted data for error checking (string). Possible values: N, E, O

    • Bytes: number of data bits (integer)

    • Stopbits: number of stop bits (integer)

    • Timeout: read timeout value in seconds (integer)

    • Data: A list of dictionaries that contain information about each data stream (one dictionary per data stream). Each dictionary has the following keys:

      • Name: data name (string)

      • Type: data type (string)

      • Scale: scaling factor (integer)

      • Conversion: conversion factor (float)

      • Channel: register number (integer)

      • Signed: define data as unsigned or signed (bool)

      • Fcode: modbus function code (integer). Possible values: 3,4

Example configuration options are shown below.

  Database: db_name
  Table: table_name
  Username: username
  Password: password
  Interval: 1 
  Retries: 2
- Name: Device1
  USB: /dev/ttyUSB0       
  Address: 21        
  Baud: 9600
  Parity: N
  Bytes: 8
  Stopbits: 1
  Timeout: 0.05
  - Name: AmbientTemp
    Type: Temp
    Scale: 1
    Conversion: 1.0
    Channel: 0
    Signed: True
    Fcode: 4
  - Name: DC Power
    Type: Power
    Scale: 1
    Conversion: 1.0
    Channel: 1
    Signed: True
    Fcode: 4