What converting a circuit to string means and why you'd do it

Converting a circuit diagram to a string format means turning a visual schematic — the boxes, lines, and labels you draw or photograph — into text that a computer can read, store, and search. The string is usually a list of components and their connections written in a format like SPICE (Simulation Program with Integrated Circuit Emphasis), JSON, or a custom text notation that your circuit software understands.

You do this so you can back up the circuit in a way that takes almost no space, survives software updates, and stays readable 10 years from now. A JPEG of a schematic can become unreadable if the image degrades or the software that made it disappears. A text string of the same circuit will open in any text editor on any device.

The conversion also lets you search your circuit files by component name, voltage, or function without opening each one individually. If you have 50 circuits and need to find every one that uses a 10-kilohm resistor, a string format makes that possible in seconds.

Key Takeaways

  • Most circuit design software can export to SPICE format or JSON, which are text-based strings that store all component and connection data without needing the original software to read them.
  • If your software does not have a built-in export function, you can manually transcribe the circuit into a structured text format by listing each component, its value, and what it connects to.
  • Store the string file as plain text (.txt) or in a standard format like .cir or .json so it remains readable across different computers and decades of software changes.
  • Test the string by importing it back into your circuit software or a free viewer to confirm all components and connections survived the conversion.

Using your circuit software's built-in export function

Most circuit design programs have an export or save-as option that converts your diagram to a text string automatically. Open your circuit in the software you used to create it, then look in the File menu for "Export", "Save As", or "Output". The options you see depend on the software.

If you use LTspice (free, made by Analog Devices), your circuit is already stored as a text file with a .cir extension. Open that file in any text editor and you will see the SPICE netlist — a string that lists every component, its value, and what nodes it connects to. No conversion needed; just copy the file to your backup location.

If you use KiCad (free, open-source), go to File > Export and choose "SPICE Netlist" or "JSON". KiCad will create a text file that describes your circuit in a format other programs can read. The JSON option is newer and more human-readable if you plan to search or edit the string by hand.

If you use Multisim or Proteus (paid software), check the File menu for "Export Netlist" or "Generate Netlist". Both can output SPICE format. Some versions also support exporting to CSV (comma-separated values), which is easier to search in a spreadsheet if you have many circuits.

Manually transcribing a circuit into string format

If your software has no export function, or if you have a circuit on paper or in a photograph, you can write the string yourself. This takes longer but requires only a text editor and patience. Start by listing every component in your circuit, then write down what each one connects to.

Use this structure for each line: ComponentType ComponentName Value Node1 Node2 [Node3 Node4]. For example, a resistor named R1 with a value of 10 kilohms connecting between nodes "in" and "out" would be written as: R R1 10k in out. A capacitor C1 of 100 microfarads between "out" and ground would be: C C1 100u out 0 (where 0 is ground).

Here is a complete example of a straightforward circuit string:

R R1 10k vcc out R R2 1k out 0 C C1 100u out 0 V V1 5 vcc 0 .end

This describes a voltage divider with a capacitor to ground. The V line defines the power supply (5 volts between node "vcc" and ground). The .end line tells the simulator the circuit definition is complete. If you are using JSON instead, the structure is different but the information is the same — each component listed with its properties and connections.

Choosing a file format that will last

Save your circuit string as plain text with one of these extensions: .txt, .cir, .sp, or .json. Avoid proprietary formats like .dwg or .sch unless you also keep a copy in a standard format. Plain text files open on any computer, any operating system, and any decade.

SPICE format (.cir or .sp) is the oldest and most widely supported. Almost every circuit simulator made in the last 30 years can read a SPICE netlist. If you want maximum future-proofing, use SPICE.

JSON format (.json) is newer and easier to read if you need to search or edit by hand. It is also becoming a standard for circuit data exchange. If your software supports JSON export, use it alongside SPICE so you have both options.

Do not rely on a single proprietary format. If you have a circuit in Multisim's native format, export it to SPICE as well. If you have a KiCad schematic, save both the .kicad_sch file and a SPICE netlist. The extra file takes almost no space and protects you if the original software becomes unavailable.

Testing your converted circuit string

Before you delete the original diagram, import the string back into your circuit software or a free simulator to confirm nothing was lost. Open the string file in the same program you used to create it, or in a free SPICE viewer like ngspice or LTspice.

Check that all components appear with the correct values and connections. If you manually transcribed the circuit, look for typos in component names or node connections — a single wrong letter will break the circuit. Run a simulation if possible; if the circuit behaves the way you expect, the conversion is correct.

If the import fails, the error message will usually point to the line that caused the problem. Common mistakes are misspelled component types (use R for resistor, C for capacitor, L for inductor, V for voltage source), missing values, or node names with spaces or special characters. Fix the error, save, and test again.

Organizing and naming your circuit strings

Store your circuit strings in a folder structure that matches how you organize the original diagrams. If you have a folder called "Audio Amplifiers", create a subfolder called "Audio Amplifiers / SPICE Strings" and put all the converted circuits there. Use a naming convention that includes the circuit name and the format: TDA7293_Amplifier_SPICE.cir or Preamp_Stage_JSON.json.

If you have many circuits, create a straightforward text file index that lists the filename, the circuit's purpose, and the components it contains. This lets you search for circuits by function without opening each file. For example: TDA7293_Amplifier_SPICE.cir | 100W audio amplifier | TDA7293, power transistors, output transformer.

Back up the strings folder to cloud storage, an external drive, or both. Since the files are text, they compress well and take almost no space. A folder with 100 circuit strings might be only 5 to 10 megabytes.

Frequently Asked Questions

Can I convert a circuit photograph or PDF schematic to a string?

Not automatically. You would need to manually transcribe it by reading the diagram and typing each component and connection into a text file. If the PDF is a vector drawing (not a raster image), some circuit software can import it directly and then export to SPICE. For a photograph, manual transcription is the only option.

What if my circuit software does not support SPICE export?

Check if it supports JSON, CSV, or any text-based format. If not, export to a standard image format (PDF or SVG) and manually transcribe the circuit into SPICE or JSON. The transcription takes time but ensures you have a future-proof backup.

Will a SPICE string work in every circuit simulator?

Most simulators support SPICE, but some use slightly different syntax for advanced features. A basic SPICE netlist with resistors, capacitors, inductors, and voltage sources will work everywhere. If your circuit uses specialized components or simulation commands, test it in the target simulator before relying on it.

How do I search multiple circuit strings for a specific component?

Use your operating system's file search tool (Windows Search, macOS Spotlight, or Linux grep) to search for the component value or name across all .cir or .txt files in your circuits folder. For example, searching for "10k" will find every circuit that uses a 10-kilohm resistor.

Should I keep both the original diagram and the string version?

Yes. The diagram is easier to understand visually, and the string is easier to search and back up. Keep both in your organized folder structure. The diagram file is your working copy; the string is your long-term archive.