eelib.py

#!/usr/bin/python3

import time
import sys
import math
import re
import struct
import enum
import pyvisa

def errprint(*args, **kwargs):
	print(*args, file=sys.stderr, **kwargs)
	
def norm_angle(x: float) -> float:
	"""Normalizes angle to value between [-180,180[."""
	x = x % 360
	if x >= 180:
		x -= 360
	elif x < -180:
		x += 360
	return x

def vunit(v):
	"""Returns voltage with proper unit."""
	units = ("V", "mV", "uV")
	factors = (1, 1e-3, 1e-6)
	for i in range(0, len(units)):
		if abs(v) >= factors[i]: return f"{v / factors[i]}{units[i]}"
	return "1uV"

def active_channels():
	"""Returns active DSO channels."""
	channels = []
	for ch in ['C1', 'C2', 'C3', 'C4']:
		s = dso.query(f"{ch}:TRA?").strip()
		match = re.search("^(C\d):TRA ON$", s)
		if match: channels.append(match.group(1))
	return channels

def vautoscale(ch, iterations = 2, vdiv = 7.5):
	"""Automatic vertical offset and scale adjustment."""
	# Measures Vmin and Vmax, then adjusts vertical offset and scale
	for i in range(0, iterations):
		if i > 0: time.sleep(0.1)
		s = dso.query(f"{ch}:PAVA? MIN").strip()
		match1 = re.search("^C\d:PAVA MIN,(.*)V$", s)
		s = dso.query(f"{ch}:PAVA? MAX").strip()
		match2 = re.search("^C\d:PAVA MAX,(.*)V$", s)
		if match1 and match2 and not match1.group(1).startswith("*") and not match2.group(1).startswith("*"):
			vmin = float(match1.group(1))
			vmax = float(match2.group(1))
			vpp = vmax - vmin
			v0 = vmin + vpp / 2
			dso.write(f"{ch}:OFST {-v0:.5f}V")
			dso.write(f"{ch}:VDIV {vpp / vdiv:.5f}V")
		else:
			errprint(f"Error parsing for vautoscale: {s}")
			sys.exit(1)

def hscale(f):
	"""Computes optimal horizontal scale for given frequency."""
	t = 1 / (f * 4)
	units = ("ns", "us", "ms", "s")
	factors = (1e-9, 1e-6, 1e-3, 1)
	for i in range(0, len(units)):
		for j in (1, 2, 5, 10, 20, 50, 100, 200, 500):
			if j * factors[i] > t: return f"{j}{units[i]}"
	return "1s"

def dBV(v):
	return 20 * math.log10(v)

def measure_hscale():
	"""Returns horizontal scale per division."""
	s = dso.query(f"TDIV?").strip()
	match = re.search("^TDIV ([-+0-9.E]+)S$", s)
	if match:
		t = float(match.group(1))
	else:
		errprint(f"Error parsing: {s}")
		sys.exit(2)
	return t

def measure_vpp(ch):
	"""Returns Vpp of given DSO channel."""
	# Assumes optimal vertical scale
	s = dso.query(f"{ch}:PAVA? PKPK").strip()
	match = re.search("^C\d:PAVA PKPK,(.*)V$", s)
	if match and not match.group(1).startswith("*"):
		vpp = float(match.group(1))
	else:
		errprint(f"Error parsing Vpp: {s}")
		sys.exit(2)
	return vpp

def measure_mean(ch):
	"""Returns mean of given DSO channel."""
	# Assumes optimal vertical scale
	s = dso.query(f"{ch}:PAVA? MEAN").strip()
	match = re.search("^C\d:PAVA MEAN,(.*)V$", s)
	if match and not match.group(1).startswith("*"):
		v = float(match.group(1))
	else:
		errprint(f"Error parsing V: {s}")
		sys.exit(2)
	return v

def measure_level(ch):
	"""Returns V of given DSO channel at the trigger point."""
	# Assumes optimal vertical scale
	s = dso.query(f"{ch}:PAVA? LEVELX").strip()
	match = re.search("^C\d:PAVA LEVELX,(.*)V$", s)
	if match:
		sample = float(match.group(1))
	else:
		errprint(f"Error parsing: {s}")
		sys.exit(2)
	return sample

def measure_phase(ch1, ch2):
	"""Returns phase difference between two DSO channels."""
	# Assumes optimal horizontal and vertical scales
	dso.write(f"{ch2}-{ch1}:MEAD? PHA") # Query returns extra \xa1\xe3 data, so using read_raw
	s = dso.read_raw()[:-2].decode()
	match = re.search("^C\d-C\d:MEAD PHA,(.*)$", s)
	if match:
		if match.group(1).startswith("*"):
			phase = 0
		else:
			phase = norm_angle(float(match.group(1)))
	else:
		errprint(f"Error parsing phase: {s}")
		sys.exit(4)
	return phase

def close_resources():
	for instr in resources:
		resources[instr].close()

rm = pyvisa.ResourceManager()
resources = {}
for instr in rm.list_resources():
	match = re.search("::SDS.*::INSTR$", instr)
	if match:
		resources['dso'] = rm.open_resource(instr)
	match = re.search("::SDG.*::INSTR$", instr)
	if match:
		resources['awg'] = rm.open_resource(instr)

dso = resources['dso'] if 'dso' in resources else None
awg = resources['awg'] if 'awg' in resources else None

# Module Tests
if __name__ == "__main__":
	assert norm_angle(240) == -120
	assert vunit(2.5e-3) == "2.5mV"