realtime_chart.py

#!/usr/bin/env python
import numpy
import matplotlib.pyplot as plot

from pyusbtmc import RigolScope

""" Example program to plot the Y-T data from Channel 1"""

def getChannelData(channel):
    if (channel==1):
        channelName = "CHAN1"
    elif (channel==2):
        channelName = "CHAN2"
    else:
        print "Invalid channel!"
        return

    # Grab the data from channel 1
    test.write(":WAV:POIN:MODE NOR")

    test.write(":WAV:DATA? " + channelName)
    rawdata = test.read(9000)
    data = numpy.frombuffer(rawdata, dtype='B', offset=10)

    # Get the voltage scale
    test.write(":" + channelName + ":SCAL?")
    voltscale = float(test.read(20))

    # And the voltage offset
    test.write(":" + channelName + ":OFFS?")
    voltoffset = float(test.read(20))

    # Walk through the data, and map it to actual voltages
    # First invert the data (ya rly)
    data = data * -1 + 255

    # Now, we know from experimentation that the scope display range is actually
    # 30-229.  So shift by 130 - the voltage offset in counts, then scale to
    # get the actual voltage.
    data = (data - 130.0 - voltoffset/voltscale*25) / 25 * voltscale + voltoffset

    # Get the timescale
    test.write(":TIM:SCAL?")
    timescale = float(test.read(20))

    # Get the timescale offset
    test.write(":TIM:OFFS?")
    timeoffset = float(test.read(20))

    # Now, generate a time axis.  The scope display range is 0-600, with 300 being
    # time zero.
    time = numpy.arange(-300.0/50*timescale, 300.0/50*timescale, timescale/50.0)

    # If we generated too many points due to overflow, crop the length of time.
    if (time.size > data.size):
        time = time[0:600:1]

    # See if we should use a different time axis
#    if (time[599] < 1e-3):
#        time = time * 1e6
#        tUnit = "uS"
#    elif (time[599] < 1):
#        time = time * 1e3
#        tUnit = "mS"
#    else:
#        tUnit = "S"
    return [time, data]


# Initialize our scope
test = RigolScope("/dev/usbtmc0")

plot.ion()

while 1:
    t1, d1 = getChannelData(1)
    t2, d2 = getChannelData(2)

    # Start data acquisition again, and put the scope back in local mode
    test.write(":KEY:FORC")

    # Plot the data
    plot.clf()
    plot.plot(t1, d1)
    plot.plot(t2, d2)
    plot.title("Oscilloscope data")
    plot.ylabel("Voltage (V)")
    plot.xlabel("Time (s)")
    plot.xlim(t1[0], t1[599])
    plot.draw()