Analog I/O

This example code shows how to use analog inputs and outputs in a data acquisition loop. Random voltage outputs (between 0 and 5 V) are generated at a constant time interval of 0.5 s on ports DAC0 and DAC1. Ports AIN0 and AIN1 are used to sample the voltages as fast as possible. The data acquisition latency (in average under 2 ms) is due mostly to the LabJack I/O times. Accurate time execution of output events can be achieved by the use of a timer logic in the loop.

""" lj_io_analog.py

Uses analog input and output channels.

This example shows how to use analog inputs and outputs in a data acquisition
loop. Accurate time execution of output events can be achieved by the use of a
timer logic in the loop. The voltage measurements are executed as fast as
possible. The main latency source is the LabJack I/O times.

Setup:
    Connect DAC0 to AIN0
    Connect DAC1 to AIN1

The LabJack unified methods in this example are:
    set_analog ....... Writes analog value to specified port(s)
    get_analog ....... Reads analog value from specified port(s)
    close ............ Closes the LabJack device

"""
import time
import numpy as np
from labjack_unified.utils import plot_line
from labjack_unified.devices import LabJackU3, LabJackU6, LabJackT7

# To use a LabJack U6 or a T7, change the device name
# from LabJackU3 below to either LabJackU6 or LabJackT7
lj = LabJackU3()

# Assigning parameters
tstep = 0.5 # Interval between step changes (s)
t = [] # Output time array
v1 = [] # Output sampled voltage 1 array
v2 = [] # Output sampled voltage 2 array

# Initializing timers and starting main clock
tprev = 0
tcurr = 0
tstart = time.perf_counter()
# Executing acquisition loop
print('Running code for 5 seconds ...')
while tcurr <= 5:
    # Updating analog output every `tstep` seconds
    # with random voltages between 0 and 5 V
    if (np.floor(tcurr/tstep) - np.floor(tprev/tstep)) == 1:
        lj.set_analog('DAC0', 5*np.random.rand())
        lj.set_analog('DAC1', 5*np.random.rand())
    # Updating previous time and getting current time (s)
    tprev = tcurr
    tcurr = time.perf_counter() - tstart
    # Acquiring analog data as fast as possible
    # and appending values to output arrays
    t.append(tcurr)
    v1.append(lj.get_analog('AIN0'))
    v2.append(lj.get_analog('AIN1'))
print('Done.')
# Closing the device
lj.close()
del lj

# Plotting results
plot_line([t]*2, [v1, v2], yname=['AIN0', 'AIN1'], axes='multi', marker=True)
plot_line([t[1::]], [1000*np.diff(t)], yname=['Sampling Period (ms)'])