How to Make an RLC Circuit in Python

Daniyal Ahmed

9 months ago

I’m the kind of developer who learns best when I see something appear on-screen. So when I found out that Schemdraw can turn a few lines of Python into a polished schematic, I had to try it. Below is the full journey: the bare-bones code, the inevitable error I hit, the upgrades I bolted on, and a handful of practice ideas you can steal

My Code

schemdraw
import schemdraw.elements as elm

d = schemdraw.Drawing()

V = d.add(elm.SourceV().label('V', loc='left'))  # Voltage source
R = d.add(elm.Resistor().label('R').right())     # Resistor
C = d.add(elm.Capacitor().label('C').right())    # Capacitor
L = d.add(elm.Inductor().label('L').right())     # Inductor

d.add(elm.Ground().at(V.start))  # Ground at the negative terminal
d.add(elm.Ground().at(L.end))    # Ground at the far end

d.draw()

Run that after installing Schemdraw (pip install schemdraw) and you’ll see a neat series R-C-L network with the source on the left and ground rails at both ends.

Explain Code

Line	What I typed	What it actually does
`import schemdraw`	Pulls in the library	Gives me the `Drawing` class and plotting backend
`import schemdraw.elements as elm`	Shortcut alias	Lets me reference parts as `elm.Resistor()` instead of the long path
`d = schemdraw.Drawing()`	Makes a blank canvas	All later parts attach to this object
`V = d.add(elm.SourceV()...)`	Adds a voltage source	I label it V and pin the label to the left
`R = d.add(elm.Resistor().right())`	Adds a resistor to the right	`.right()` makes the next part start where the last one ended
`C = d.add(elm.Capacitor()...)`	Adds the capacitor	Same chaining trick
`L = d.add(elm.Inductor()...)`	Adds the inductor	Finishes the series string
`d.add(elm.Ground().at(V.start))`	Drops ground at the source’s minus side	Keeps the drawing tidy and realistic
`d.draw()`	Renders the figure	Opens a Matplotlib window or saves if I choose

The First Error

ModuleNotFoundError: No module named 'schemdraw'

I forgot to install the package on this machine. A quick:

pip install schemdraw

sorted it out.

Other hiccups you might see:

Error text	Why it shows up	Quick cure
`AttributeError: 'SourceV' object has no attribute 'start'`	You’re on an ancient Schemdraw (< 0.15)	`pip install --upgrade schemdraw`
“Blank figure” on a headless server	No GUI backend for Matplotlib	Add:

import matplotlib  
matplotlib.use('Agg')

and call d.save('circuit.png') instead of d.draw() |

Correct Code

I wanted labels, automatic PNG export, and a quick “netlist” print-out so students can map nodes. Here’s the result:

import schemdraw
import schemdraw.elements as elm
import matplotlib
matplotlib.use('Agg')  # comment out for an interactive window

def draw_series_rlc(v_label='V',
                    r_val='10 Ω',
                    c_val='1 µF',
                    l_val='100 mH',
                    fname='series_rlc.png'):
    """
    Draw a labelled series RLC circuit and save it.
    """
    d = schemdraw.Drawing()

    V = d.add(elm.SourceV().label(v_label, loc='left'))
    R = d.add(elm.Resistor().label(r_val).right())
    C = d.add(elm.Capacitor().label(c_val).right())
    L = d.add(elm.Inductor().label(l_val).right())

    d.add(elm.Ground().at(V.start))
    d.add(elm.Ground().at(L.end))

    d.save(fname)
    print(f'Diagram saved to {fname}')

    # mini-netlist for spice fans
    print('\nNetlist:')
    print('N1 V  0')
    print(f'N1 R N2 {r_val}')
    print(f'N2 C N3 {c_val}')
    print(f'N3 L 0  {l_val}')

if __name__ == '__main__':
    draw_series_rlc()      # uses the defaults

Define Change

Parameters let me swap part values without hacking the code.
The picture drops to series_rlc.png handy for slides or lab sheets.
The quick netlist means I can paste straight into SPICE and simulate.

Explain Code

Tweak the values

draw_series_rlc(r_val='47 Ω', c_val='4.7 nF', l_val='220 µH')

Re-order parts
Move the capacitor first and watch how the diagram updates.
Add a parallel branch

d.push(); d.add(elm.Capacitor().down()); d.pop()

Export to SPICE
Pipe the printed netlist into LTspice or ngspice, then compare the step response.
Color-code elements
Pass color='blue' into any element call to highlight it for teaching.

Final Thought

Drawing circuits in code felt gimmicky until I tried it. Now I reach for Schemdraw every time I need a quick schematic for notes, slides, or blog posts like this. The library is tiny, the API is readable, and the payoff a clean vector graphic in seconds beats hand-fiddling in a GUI.