resistor

Find optimal resistor configurations for a target resistance using E-series standards.

Given a target resistance, this tool finds the best single resistor or two-resistor combination (series or parallel) from the E-series standard values, ranked by how well the tolerance envelope contains the target.

Installation

pip install resistor

Or install from source:

git clone https://github.com/commuted/resistor.git
cd resistor
pip install -e .

Usage

Command Line

# Find configurations for 1580 ohms
resistor 1580

# Supports k (kilo) and M (mega) suffixes
resistor 4.7k
resistor 2.2M

# Show more results
resistor 1580 -n 10

# Use different E-series (E24 instead of E96)
resistor 1580 -e 24

# Use 5% tolerance resistors
resistor 1580 -t 5

# Only show single/series/parallel results
resistor 1580 --single-only
resistor 1580 --series-only
resistor 1580 --parallel-only

Python API

from resistor import (
    find_best_resistor_config,
    create_table,
    create_series_table,
    create_parallel_table,
)

# Create lookup tables (do once, reuse for multiple queries)
base_table = create_table(es=96, decades=6, tolerance=0.01)
series_table = create_series_table(base_table)
parallel_table = create_parallel_table(base_table)

# Find best configurations for target
results = find_best_resistor_config(
    target=1580,
    base_table=base_table,
    series_table=series_table,
    parallel_table=parallel_table,
    n=5
)

for r in results:
    print(f"{r['config']}: {r['resistors']} = {r['nominal']}Ω")

How It Works

1. Generates E-series values (default E96) across multiple decades with tolerance bounds
2. Computes all series combinations: R_total = R1 + R2
3. Computes all parallel combinations: R_total = (R1 × R2)/(R1 + R2)
4. Scores each configuration by how well the tolerance envelope contains the target
5. Returns top-n results sorted by score

The scoring function returns 0 if the target falls within the tolerance envelope, otherwise returns the normalized distance to the nearest bound. A small tiebreaker based on relative error ensures consistent ordering for equal scores.

E-Series Standards

The E-series (IEC 60063) defines preferred number values for electronic components:

Series	Values/Decade	Typical Tolerance
E6	6	20%
E12	12	10%
E24	24	5%
E48	48	2%
E96	96	1%
E192	192	0.5%

Development

# Install dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run tests with coverage
pytest --cov=resistor --cov-report=term-missing

License

MIT