kspi / betapot

Beta CDF potentiometer curve generator

betapot

Generate and plot potentiometer curve lookup table using the Beta cumulative distribution function.

There are two parameters that determine the curve shape: A and B. If both are 1, the curve is linear. If <1, that part of the curve (bottom or top) becomes steeper. If >1 it becomes flatter.

Below is a grid of plots showing how parameters affect the curve. X axis is input, Y axis is output.

Outputs comma separated values suitable for inclusion in a C array.

Setup

The program depends on Python 3, numpy, scipy (that you should install using your package manager), matplotlib and seaborn. In case the last ones are not available, you can use pip:

pip3 install --user -r requirements.txt

Usage

usage: betapot.py [-h] [--no-plot] [--size SIZE] [--min MIN] [--max MAX]
                   [--output OUTPUT]
                   A B

positional arguments:
  A                bottom flatness
  B                top flatness

optional arguments:
  -h, --help       show this help message and exit
  --no-plot        don't plot preview
  --size SIZE      size of lookup table (default: 256)
  --min MIN        minimum output value (default: 0)
  --max MAX        maximum output value (default: 255)
  --output OUTPUT  output file (default: stdout)

For example, save a curve to pot.inc using

./betapot.py --no-plot --output=pot.inc 0.9 1.3

then include the file from your C code:

static const uint8_t pot_curve[] = {
#include "pot.inc"
};