Digipyze

This repository contains a python script used to digitalize a battery curve and to extract the parameters to insert in MESSY.

Preparing the virtual environment

Since we are dealing with some external python libraries, we need to prepare a virtual environment and install all the needed libraries. To do that just enter in the folder where you clone this repository and run:

python3 -m venv venv

Then you need to activate it by running:

source venv/bin/activate

Now you can install all the packages contained in the requirements.txt file by running:

pip3 -r install rquirements.txt

Everything now should be ready and you can move on to the next step!

Using PlotDigitalizer

First of all, we need to digitalize al least TWO of the curve from the datasheet. It is important to use the discharge characteristics, which is a Voltage vs Capacity plot, like the following

To do that, we use an online Tool, called PlotDigitizer. When you open the website and launch the app, you will be promped to upload an image. When the image is uploaded, you should find 4 points, labelled as x1, x2, y1 and y2. This are used to calibrate the measurments.

Now move the 4 points in meaningful parts of the graph, as shown in the following pictures. As you can see, we moved x1 and y1 in the point (0, 3), while x2 is in (35, 3) and y2 is in (0, 4.5).

Note

If you don't clearly see x1 and y1 is because they are one on top of the other in the point (0, 3)

In the top right of the screen you should see a window where you can enter the value of the points.

Just enter the values of the points, so that the system is calibrated

Now, if you click in any part of the plot, you should see a white point appearing. This means that a point has been captured and you should see a list of point on the top left of the screen. You can now select a curve, for example 1C, and select some white point to follow the curve.

Note

You can select as much point you want, the more the better. However, selecting around 15-20 points should be a reasonable value and will allow to obtain good accuracy.

When you are happy with the selected number of points, just click the copy button on the top left to select all the points. Paste the output into a .txt file, which will be the file containing the points of your first curve.

Now repeat the procedure for another curve, different from the one already digitalized.

Warning

The tool allows to digitalize one line at a time. To digitalize the other one, just repeat the process from scratch, calibrate, select some points and then paste them into another .txt.

How to run it

Now you should have two .txt files, where you have the points of the two curves. The files should look something like this:

x, y
0.03410000,  3.00830000
0.04210000,  3.04570000
0.07820000,  3.14540000
0.09820000,  3.19110000
0.14030000,  3.26180000
0.20040000,  3.35320000
0.24450000,  3.41140000
0.30460000,  3.48610000
0.33670000,  3.51520000
0.39280000,  3.56090000
0.47700000,  3.60660000
0.55510000,  3.64400000
0.63730000,  3.70220000
0.70940000,  3.75620000
0.79360000,  3.83100000
0.83970000,  3.88500000
0.89780000,  3.95980000
0.93790000,  4.03460000
0.97190000,  4.09700000
0.98800000,  4.17590000
0.99600000,  4.23820000

In the folder curves you find two examples of two .txt files extracted by the characteristic showed before.

Now that everything is ready, you can run the python script passing the correct command line arguments to compute the parameters of polynomial.

The command line arguments are the following:

Name	Type	Description
first-curve-file	String	Path to the first curve .txt file
second-curve-file	String	Path to the first curve .txt file
battery-capacity	Int	Capacity of the battery in mAh

Warning

The capacity of the battery MUST be in mAh

python3 prova.py --first-curve-file first_curve_filename.txt --second-curve-file second_curve_filename.txt --battery-capacity battery_capacity_in_mAh