schematic-diagram

Schematic Diagram Generator

Turn a natural-language circuit description into a clean Graphviz DOT file, render it as SVG and PNG, and save all three to the working directory.

Step 1 — Analyse the description

Read the full schematic description and extract:

• Components: every part (IC, transistor, passive, connector, LED, sensor, relay, motor, encoder, driver, converter, display, SBC, power source…)
• Functional groups: cluster parts that belong together logically
• Connections: every wire, including the pin name at both ends
• Power nets: named rails like VCC, GND, 12V, 5V, 3V3, VCC_SWITCHED — model prominent intermediate rails as separate diamond-shaped nodes, not just edge labels
• Signal direction: which end drives, which end receives (determines arrow direction)
• Bus types: I2C, SPI, UART, CAN, PWM, quadrature encoder — these become dashed edges

Step 2 — Choose the layout archetype

Pick the archetype that best matches the circuit, then arrange functional groups left → right:

A) Energy / power flow

[Source (PV/battery)] → [Conversion/management] → [Switching stage] → [Loads]

Use when the dominant story is where power comes from and how it is switched/converted. Examples: solar charger, MPPT + relay management, precharge circuit, DC-DC converter chain.

B) Sense → Control → Act

[Sensors / inputs] → [MCU / controller] → [Drivers] → [Actuators]

Use when an MCU processes inputs and drives outputs. Examples: motor controller, robot drive system, PID loop, Arduino + H-bridge.

C) Multi-board / distributed system

[Board A (e.g. Pi)] ←serial/I2C→ [Board B (e.g. MEGA)] ←GPIO→ [Board C (Pro Mini)]

Arrange boards as peer columns; connect with labelled bus edges. Use when several MCUs/SBCs exchange data.

D) Bus-centric

[Peripheral 1]
[Peripheral 2]  ←── I2C/SPI bus ──→  [MCU / bus master]
[Peripheral 3]

Use when one bus ties many peripherals to one master (I2C sensors, SPI devices).

Mixed circuits

Combine archetypes: place the energy/power layer at the top of the diagram (using subgraph cluster_power) and the control/signal layer below it. Connect them with power-supply edges.

Each functional group becomes a subgraph cluster_X { … }. Flat clusters are usually better than deeply nested ones.

Step 3 — Write the DOT file

Graph-level settings

digraph <CamelCaseName> {
    graph [
        rankdir=LR
        fontname="Arial"
        fontsize=14
        label="<Human-readable title>"
        labelloc=t
        labeljust=c
        splines=spline       // spline avoids the edge-through-cluster problem of ortho; curved is incompatible with taillabel/headlabel
        nodesep=0.9
        ranksep=2.0
        compound=true
        bgcolor=white
        pad=0.8
    ]
    node [fontname="Arial" fontsize=10 style="filled,rounded" shape=box margin="0.2,0.12"]
    edge [
        fontname="Arial"
        fontsize=9
        penwidth=1.5
        labelfontsize=9
        labeldistance=2.4
        labelangle=25
    ]
}

GND symbols — one per cluster, never one global one

A single global GND node creates a fan of long, crossing lines. Instead declare one GND symbol per cluster and connect it locally:

// declare all at once after the global node defaults
node [shape=invtriangle style=filled fillcolor="#444444" fontcolor=white
      fontsize=8 width=0.4 height=0.28 margin="0.04,0.04" label="GND"]
gnd_pwr  gnd_ctrl  gnd_mcu  gnd_drv  gnd_sens

// then restore normal node style
node [shape=box style="filled,rounded" fontsize=10 fontcolor=black margin="0.2,0.12"]

Each cluster uses only its own GND symbol.

Cluster color palette

Functional role	fillcolor	color (border)
Energy source (PV, battery)	#FFF8E1	#E65100
Power conversion (MPPT, DC-DC, reg)	#FCE4EC	#880E4F
Switching / relay stage	#E3F2FD	#1565C0
MCU / microcontroller / SBC	#E8F5E9	#2E7D32
Motor driver / H-bridge / ULN	#FFF3E0	#E65100
Actuator (motor, brush, servo)	#FBE9E7	#BF360C
Sensor / measurement / ADC	#F3E5F5	#6A1B9A
Communication / display	#E0F2F1	#00695C
Intermediate power rail ◇	#FFF3CD	#CC7700

Choose the role that best describes each cluster. It is fine to use the same color for two clusters of the same role.

Intermediate power rails as diamond nodes

RAIL_5V [
    label="5 V Rail\n(XL4015 out)"
    shape=diamond
    fillcolor="#FFF3CD" color="#CC7700" penwidth=2.8
    width=2.0 height=1.0 fontsize=10
]

Component node shapes

Component type	Recommended shape / notes
MCU, Arduino, SBC (Pi, MEGA)	shape=box — large: width=2.0–2.8 height=1.4–1.8
Simple IC (timer, driver)	shape=box — medium: width=1.6–2.0 height=1.0–1.4
Relay (bistable or standard)	shape=box — add coil/contact info in label
H-bridge / motor driver	shape=box — label includes EN/PWM pins
DC-DC converter	shape=box — label: input/output voltages
Battery / accumulator	shape=cylinder width=1.1 height=1.2
Solar panel	shape=box — label: Vmp, Wp
Passive (R, C, L)	shape=box — small: width=0.9 height=0.7
LED / indicator	shape=ellipse width=1.1 height=0.7
Transistor (BJT, MOSFET)	shape=box width=1.5 height=1.1
Encoder / end switch	shape=box — small, note signal type in label
Display (OLED, LCD)	shape=box width=1.8 height=1.0
Current / voltage sensor	shape=box — label with I2C address if known

Edge conventions — pin labels at both ends

Every edge must carry taillabel (pin at source) and headlabel (pin at destination). Match labelfontcolor to the edge color:

// GPIO control signal
ProMini -> ULN2003 [
    taillabel="D7 (R3_SET)"  headlabel="IN3"
    color="#1565C0" penwidth=2 labelfontcolor="#1565C0"
]

// Serial bus between boards
RPi -> MEGA [
    taillabel="TX (GPIO14)"  headlabel="RX0"
    color="#00695C" style=dashed penwidth=2 labelfontcolor="#00695C"
    label="UART 115200"
]

Edge color guide

Net / signal type	color	style
High-power supply (battery, PV)	#E65100	solid
Regulated / switched power	#CC7700	solid
Motor drive / PWM output	#BF360C	solid
Control / GPIO / relay coil	#1565C0	solid
I2C / SPI bus	#00695C	dashed
UART / Serial	#00838F	dashed
Analog signal / ADC input	#6A1B9A	solid
Encoder / quadrature	#4527A0	solid
Generic data bus	#2E7D32	dashed
GND return	#444444	solid

Backward / cross-layer edges

When power bypasses the normal left-to-right flow (e.g. battery feeds a load directly), add constraint=false to avoid rank distortion:

BAT -> MEGA [
    taillabel="12 V+"  headlabel="VIN"
    color="#E65100" penwidth=2 labelfontcolor="#E65100"
    constraint=false
]

Dashed edges for buses

MEGA -> INA260 [
    taillabel="SDA/SCL"  headlabel="SDA/SCL (0x40)"
    color="#00695C" style=dashed penwidth=2 labelfontcolor="#00695C"
    label="I2C"
]

Relay nodes with dual-coil labels

For bistable relays, include SET/RST coil pins in the label:

R1 [
    label="Relay R1\n(bistable 12 V)\nSET←R1_SET | RST←R1_RST\nSwitches: PV → Victron"
    shape=box width=2.2 height=1.3
    fillcolor="#E3F2FD" color="#1565C0" penwidth=2
]

Step 4 — Render to SVG and PNG

MANDATORY: use the system dot binary (graphviz package) — nothing else. Do NOT use viz.js, npm, node, cairosvg, or any other rendering tool. Do NOT create /tmp/viz_test or any npm project. The only permitted commands are dot -Tsvg … and dot -Tpng ….

Check for graphviz — run this first, before writing any DOT file

which dot 2>/dev/null && dot -V 2>&1 || echo "GRAPHVIZ_MISSING"

If the output contains GRAPHVIZ_MISSING: Stop immediately. Do not write any file. Tell the user:

Graphviz ist noch nicht installiert. Bitte tippe diesen Befehl direkt in den Chat (das !-Präfix öffnet eine interaktive Shell mit Passwort-Prompt):

! sudo apt install -y graphviz

Sobald das erledigt ist, sag kurz "fertig" und ich rendere das Diagramm.

Wait for the user's confirmation, then re-run the which dot check before continuing.

Render DOT → SVG + PNG

dot -Tsvg <input.dot> -o <output.svg>
dot -Tpng -Gdpi=144 <input.dot> -o <output.png>

-Gdpi=144 gives 2× resolution — sufficient for screen and A4 print.

Step 5 — Save outputs and report

Save three files to the working directory (use a short, descriptive base name):

File	Content
<name>.dot	Editable DOT source
<name>.svg	Scalable vector graphic
<name>.png	Rasterized PNG (144 dpi)

Report the file paths and briefly describe what was grouped into each cluster.

Common pitfalls

Problem	Fix
Edges route through cluster boxes	Use splines=spline, not splines=ortho or curved
All GND lines converge messily	One local gnd_X per cluster
Battery → load edge bends backwards	Add constraint=false
Pin labels overlap nodes	Increase labeldistance (try 2.4–3.0)
Clusters overlap each other	Increase ranksep (try 2.0–2.5)
Labels too small to read	labelfontsize=9, render PNG at -Gdpi=144 or higher
Multi-board layout looks tangled	Use archetype C or D; make each board its own cluster
I2C/UART bus fans out messily	Group all bus edges from one cluster, use lhead/ltail