Model/Automate Passive Components for Current Amp Network

.gitignore

@@ -19,3 +19,6 @@ fp-info-cache
 *.gbrjob
 *.drl
 *.csv
+
+.venv/
+venv/

README.md

@@ -1,11 +1,18 @@
 # Getting Started with A-Team Electrical
 
-## Setting Up the Library Path
+## Setting Up the KiCAD Library Path
 - Click `Preferences->Configure Paths`
 - Under `Environment Variables` click `+`
 - Set the name `LIB_DIR_AT`
 - Set the path to `<repository_location>/lib` where <repository_location> is the download location.
 
 Example entry:
 - Name: `LIB_DIR_AT`
-- Path: `C:\Users\guyfl\Documents\A-Team\electrical\lib`
+- Path: `C:\Users\guyfl\Documents\A-Team\electrical\lib`
+
+# Setting Up the Python Environment
+ 1. We recommend creating a python environment using `python3 -m venv venv`
+ 2. Install poetry `pip install poetry`
+ 3. Run any python file with `poetry run python <python_file>`
+ 4. (Optional) Add dependencies with `poetry add <dependency>`
+

pyproject.toml

@@ -0,0 +1,20 @@
+[tool.poetry]
+name = "ateam-electrical"
+version = "0.1.0"
+description = "PCBs, Spice Models, Supporting Analysis Scripts for SSL A-Team"
+authors = ["Your Name <you@example.com>"]
+license = "MIT License"
+readme = "README.md"
+packages = [{include = "ateam_electrical"}]
+
+[tool.poetry.dependencies]
+python = "^3.8"
+numpy = "^1.23.3"
+matplotlib = "^3.6.0"
+eseries = "^1.2.1"
+uliengineering = {git = "https://github.com/ulikoehler/UliEngineering.git"}
+
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"

spice_models/motor_current_sense/calc_passives.py

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+# Calculates passive values for the motor current sensing network
+# these can be loaded into the adjacent spice models to
+# see the network response
+#
+# The dev board amplifier network equations are specified in
+# ST Microelectronics Application Note AN5397. Variable names in this
+# script will use identical names and equation references. We use the
+# variant of the network in Figure 8, but with a non-symmetrical DC
+# offset.
+# https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjd26rjm8P6AhWyj4kEHeTmAPgQFnoECBIQAQ&url=https%3A%2F%2Fwww.st.com%2Fresource%2Fen%2Fapplication_note%2Fan5397-current-sensing-in-motion-control-applications-stmicroelectronics.pdf&usg=AOvVaw2--yddSoA57WRf8KFsh-lz
+#
+# It's also noted the STSPIN (stspin32f0(?a|b)) internal amplifier
+# doesn't have a spice model or internal chart, just characteristic
+# parameters. Ryo identified LTC6241 a similar part, so it's parameters
+# are used here as needed.
+#
+# Generally, one should set I_max and V_motor
+
+import eseries
+import math
+from UliEngineering.Electronics import VoltageDivider
+
+############################
+#  user adjustable params  #
+############################
+
+# maximum current we want to accurately sense
+# df45 50W and 65W are rated for 2.36A, and 3.26A respectively
+# ecu22048h24 is rated for 2.94A, h18 (not using) is rated for 4.04A
+# we pick 4.0A to give us some margin for noise/error
+# NOTE: stalled motor will greatly exceed this, but that's ok
+I_max = 4.0
+
+# 6C LiPo battery, full charged is 4.2V/cell
+V_motor_max = 4.2 * 6.0
+
+# max resistor wattage
+P_max_W = 1.0
+
+num_adc_bits = 10
+
+###########################
+#  non-adjustable params  #
+###########################
+
+operating_boundary_margin_v = 0.25
+Vgnd = 0.0
+Vdda = 3.3
+
+V_amp_output_min = Vgnd + operating_boundary_margin_v
+V_amp_output_max = Vdda - operating_boundary_margin_v
+
+# @48KHz PWM frequency
+ltc6241_gain_db = 32.0
+# dB = 20 * log_10(V1/V2) ~ 10^(db / 20) = V
+ltc6241_gain_lin = 10 ** (ltc6241_gain_db / 20)
+# print(f"Amplifier maximum linear V/V gain: {str(round(ltc6241_gain_lin, 3))}")
+an5397_recommended_R1_E96 = 2.37e3 # 2k37
+
+# P = I^2 * R
+R_sense = P_max_W / (I_max ** 2)
+print(f"maximum sense resistance: {R_sense}")
+
+# round down to preserve safe thermal/power budget
+R_sense_E24 = eseries.find_less_than_or_equal(eseries.E24, R_sense)
+
+R_sense_05 = R_sense / 2.0
+R_sense_05_E24 = eseries.find_less_than_or_equal(eseries.E24, R_sense_05)
+
+# print("")
+V_output_range = V_amp_output_max - V_amp_output_min
+# print(f"Desired amplifier output range {V_output_range}")
+
+# V = IR
+V_input_range = I_max * R_sense_E24
+V_gain_needed = round(V_output_range / V_input_range, 3)
+
+print(f"desired amplifier gain: {V_gain_needed}")
+if V_gain_needed > ltc6241_gain_lin:
+    print("WARNING: needed gain exceeds stable gain limit of the amplifier")
+
+# AN5397 eq. 13
+# G = (R2 / R1)
+r2 = V_gain_needed * an5397_recommended_R1_E96
+# it's prudent to round away (down) from the max gain to stay away from the OpAmp rails in-case
+# a very small or 0 margin is picked, otherwise we might chop off the performant range
+# R2 proportional to Gain, so also round R2 down
+r2_E96 = eseries.find_less_than_or_equal(eseries.E96, r2)
+
+actual_gain = round(r2_E96 / an5397_recommended_R1_E96, 3)
+print(f"actual amplifier gain: {actual_gain}")
+V_actual_output_range = V_input_range * actual_gain
+
+# round in the direction of higher DC offset to keep away from edges of amplifier operating region
+R_dc_offset_bottom_E96 = eseries.find_greater_than_or_equal(eseries.E96, 2 * r2_E96)
+R_dc_offset_ratio = V_amp_output_min / Vdda
+R_dc_offset_top = VoltageDivider.top_resistor_by_ratio(R_dc_offset_bottom_E96, R_dc_offset_ratio)
+# round in the direction of higher DC offset to keep away from edges of amplifier operating region
+R_dc_offset_top_E96 = eseries.find_less_than_or_equal(eseries.E96, R_dc_offset_top)
+V_dc_offset = VoltageDivider.voltage_divider_voltage(R_dc_offset_top_E96, R_dc_offset_bottom_E96, Vdda)
+
+V_actual_min_output = round(V_dc_offset, 3)
+if V_actual_min_output < V_amp_output_min:
+    print("WARNING: minimum amplifier output fell below desired minimum")
+
+V_actual_max_output = round(V_dc_offset + V_actual_output_range, 3)
+if V_actual_max_output > V_amp_output_max:
+    print("WARNING: maximum amplifier output is above desired maximim")
+
+num_adc_values = 2 ** num_adc_bits
+pct_range_used = V_actual_output_range / (Vdda - Vgnd)
+
+print("")
+print("")
+print(f"Nominal voltage range at ADC: [{V_actual_min_output}, {V_actual_max_output}]")
+print(f"Num ADC quant. steps used {math.floor(pct_range_used * num_adc_values)} ({round(pct_range_used * 100.0, 1)}%)")
+print("")
+print(f"BUY: R_sense (AN5397 Rs) resistor value {str(round(R_sense_E24, 3))} (5%, {P_max_W}W)")
+# print(f"\tALT: Buy resistor value {str(round(R_sense_05_E24, 3))} (5%) and place in parallel")
+print(f"BUY: R1 (AN5397 R1) value {str(round(an5397_recommended_R1_E96, 3))}")
+print(f"BUY: R2 (AN5397 R2) value {str(round(r2_E96, 3))} (1%)")
+print(f"BUY: R_dc_offset_lower (AN5397 2*R2 lower) value {str(round(R_dc_offset_bottom_E96, 3))} (1%)")
+print(f"BUY: R_dc_offset_upper (AN5397 2*R2 upper) value {str(round(R_dc_offset_top_E96, 3))} (1%)")
+print("")
+print("")
+print("Voltage to current mapping function")
+m = (I_max - 0.0) / (V_actual_max_output - V_actual_min_output)
+m = round(m, 3)
+b = V_actual_min_output
+b = round(b, 6)
+print(f"I = {m}*V + {b}")