examples: ad4020_example: Calculate voltage using driver scale attribute

The scale may vary according to ADC characteristics such as precision
bits, span compression, gain, etc. and also with setup properties such
as voltage reference.
Use driver provided scale to convert back to milli-voltage units which
is the standard IIO unit for voltage type channels.

Signed-off-by: Marcelo Schmitt <[email protected]>

examples/ad4020_example.py

@@ -26,7 +26,7 @@
 data = my_adc.rx()
 
 x = np.arange(0, len(data))
-voltage = data * 2.0 * vref / (2 ** 20)
+voltage = data * my_adc.voltage0.scale
 dc = np.average(voltage)  # Extract DC component
 ac = voltage - dc  # Extract AC component
 
@@ -35,7 +35,7 @@
 plt.title(dev_name.upper() + " Time Domain Data")
 plt.plot(x, voltage)
 plt.xlabel("Data Point")
-plt.ylabel("Voltage (V)")
+plt.ylabel("Voltage (mV)")
 plt.show()
 
 f, Pxx_spec = signal.periodogram(
@@ -49,7 +49,7 @@
 plt.semilogy(f, Pxx_abs)
 plt.ylim([1e-6, 4])
 plt.xlabel("frequency [Hz]")
-plt.ylabel("Voltage (V)")
+plt.ylabel("Voltage (mV)")
 plt.draw()
 plt.pause(0.05)