This script shows how to control an LED with FIO4 by deploying a Lua scripts to the LabJack. This script also demonstrates communication between this Python script and the on-board Lua scrip via user RAM.

LJ - 10.60 - lua_script_host_control.py

'''
LJ - 10.60 - lua_script_host_control.py

This script shows how to control an LED with FIO4 by deploying a Lua scripts
to the LabJack. This script also demonstrates communication between this Python
script and the on-board Lua scrip via user RAM.

Components
----------

- LabJack T4
- LED
  - Cathode (short pin) to GND
  - Anode (long pin) to FIO4
- Wires
- Breadboard

Course
------
Data acquisition and automation with LabJack
https://app.techexplorations.com/courses/labjack/

'''

from labjack import ljm
from time import sleep

def loadLuaScript(handle, luaScript):
    """Function that loads and begins running a lua script

    """
    try:
        scriptLen = len(luaScript)
        # LUA_RUN must be written to twice to disable any running scripts.
        print("Script length: %u\n" % scriptLen)
        ljm.eWriteName(handle, "LUA_RUN", 0)
        # Then, wait for the Lua VM to shut down. Some T7 firmware
        # versions need a longer time to shut down than others.
        sleep(0.6)
        #ljm.eWriteName(handle, "LUA_RUN", 0)
        ljm.eWriteName(handle, "LUA_SOURCE_SIZE", scriptLen)
        ljm.eWriteNameByteArray(handle, "LUA_SOURCE_WRITE", scriptLen, luaScript)
        ljm.eWriteName(handle, "LUA_DEBUG_ENABLE", 1)
        ljm.eWriteName(handle, "LUA_DEBUG_ENABLE_DEFAULT", 1)
        ljm.eWriteName(handle, "LUA_RUN", 1)
    except ljm.LJMError:
        print("Error while loading the lua script")
        raise

def readLuaInfo(handle):
    """Function that selects the current lua execution block and prints
       out associated info from lua
    """
    try:
        for i in range(10):
            # The script sets the interval length with LJ.IntervalConfig.
            # Note that LJ.IntervalConfig has some jitter and that this program's
            # interval (set by sleep) will have some minor drift from
            # LJ.IntervalConfig.
            sleep(1)
            print("LUA_RUN: %d" % ljm.eReadName(handle, "LUA_RUN"))
            print("Value from USER_RAM1_F32: %d" % ljm.eReadName(handle, "USER_RAM1_F32"))
            print("Interval delay from USER_RAM0_F32: %d" % ljm.eReadName(handle, "USER_RAM0_F32"))

            # Add custom logic to control the Lua execution block
            executionLoopNum = i % 2
              # This will write a new interval
              # time to RAM register USER_RAM0_F32
              # which is address 46000
            if executionLoopNum == 0:
                ljm.eWriteName(handle, "USER_RAM0_F32", 800)  # Change interval duration to 800ms
            else:
                ljm.eWriteName(handle, "USER_RAM0_F32", 200)  # Change interval duration to 200ms

    except ljm.LJMError:
        print("Error while running the main loop")
        raise


def main():
    try:
        luaScript = """print("Starting")
local count = 0

local mbWrite = MB.W

mbWrite(46000, 3, 1000) -- Set user RAM 46000 to 1000 to be used by the timer

LJ.IntervalConfig(0, 200)      -- Set interval to 1000 for 1000ms
local checkInterval = LJ.CheckInterval

local outPin = 2004 -- FIO4 register address
local led_state = 1

while true do
  if checkInterval(0) then   -- interval completed
    LJ.IntervalConfig(0,MB.R(46000,3))   -- Read the interval time from user RAM
    mbWrite(outPin, 0, 1)
    print("LED state: ", led_state)

    if led_state == 1 then
      mbWrite(46002, 3, 200)      -- Set register "USER_RAM1_F32".  Address 46002, type 3
      mbWrite(outPin, 0, 1)
      led_state = 0
    else
      mbWrite(46002, 3, 0)        -- Set register "USER_RAM1_F32".  Address 46002, type 3
      mbWrite(outPin, 0, 0)
      led_state = 1
    end
  end
end
                        """
        # Open handle to LabJack
        handle = ljm.openS("ANY", "ANY", "Peter_T4")

        info = ljm.getHandleInfo(handle)
        print("Opened a LabJack with Device type: %i, Connection type: %i,\n"
              "Serial number: %i, IP address: %s, Port: %i,\nMax bytes per MB: %i" %
              (info[0], info[1], info[2], ljm.numberToIP(info[3]), info[4], info[5]))

        loadLuaScript(handle, luaScript)
        print("LUA_RUN %d" % ljm.eReadName(handle, "LUA_RUN"))
        print("LUA_DEBUG_NUM_BYTES: %d" % ljm.eReadName(handle, "LUA_DEBUG_NUM_BYTES"))
        readLuaInfo(handle)
        ljm.eWriteName(handle, "LUA_RUN", 0) # Stop the Lua script.
                                             # If not called, the script will
                                             # continue to run.
        # Close handle
        ljm.close(handle)
    except ljm.LJMError:
        ljm.eWriteName(handle, "LUA_RUN", 0)
        # Close handle
        ljm.close(handle)
        raise
    except Exception:
        ljm.eWriteName(handle, "LUA_RUN", 0)
        # Close handle
        ljm.close(handle)
        raise

if __name__ == "__main__":
    main()