Modifications for two's complement ADC data. Display in volts.

079cb6ee · Matthieu Cattin · da09d702 · 079cb6ee
Commit 079cb6ee authored Jan 11, 2012 by Matthieu Cattin
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fmc_adc_demo.py test/fmcadc100m14b4cha/python/fmc_adc_demo.py +18 -1

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--- a/test/fmcadc100m14b4cha/python/fmc_adc_demo.py
+++ b/test/fmcadc100m14b4cha/python/fmc_adc_demo.py
@@ -26,6 +26,9 @@ from PAGE.SineWaveform import *
 # Constants declaration
 NB_POINTS = 1000

+ADC_NBITS = 16 # ADC chip is 14 bits, but shifted to 16 bits in the firmware
+ADC_FS = 10.0
+
 USB_DEVICE = "/dev/ttyUSB0"
 RS232_BAUD = 57600

@@ -42,6 +45,17 @@ def bit2string(bit):
    else:
        return 'NO'

+# Converts two's complement hex to signed
+def hex2signed(value):
+    if(value & 0x8000):
+        return -((~value & 0xFFFF) + 1)
+    else:
+        return value
+
+# Converts digital value to volts
+def digital2volt(value, full_scale, nb_bit):
+    return float(value) * float(full_scale)/2**nb_bit
+
 def acq_plot():
    if(1 == m.nb_shot.value()):
        trig_pos = fmc.get_trig_pos()
@@ -55,6 +69,9 @@ def acq_plot():
        print('Multi-shot acq')
        channels_data = spec_fmc.get_data(0, (NB_POINTS*8))

+    channels_data = [hex2signed(item) for item in channels_data]
+    channels_data = [digital2volt(item,ADC_FS,ADC_NBITS) for item in channels_data]
+
    #channels_data = spec_fmc.get_data(0, (NB_POINTS*8))
    print('Nb points:%d')%NB_POINTS
    print('channels data length:%d')%len(channels_data)
@@ -65,7 +82,7 @@ def acq_plot():
    m.mpl_acq.canvas.ax.plot(sample, channels_data[2::4], 'r', label='Channel 3')
    m.mpl_acq.canvas.ax.plot(sample, channels_data[3::4], 'c', label='Channel 4')
    m.mpl_acq.canvas.ax.set_xlim(0, NB_POINTS)
-    m.mpl_acq.canvas.ax.set_ylim(0, 65535)
+    m.mpl_acq.canvas.ax.set_ylim(-(ADC_FS/2)-(ADC_FS/10), (ADC_FS/2)+(ADC_FS/10))
    m.mpl_acq.canvas.ax.legend()
    m.mpl_acq.canvas.draw()