Fritzing is a freely downloadable circuit editor and electronic design automation application produced by staff and students from the Interaction Design Lab at the University of Applied Sciences in Potsdam, Germany. It allows electronic circuits to be created and edited in three different interchangeable views:
Breadboard (Prototype Board) View
Fritzing is particularly well suited for use with microcontroller-based projects, including Arduino, due to its extensive library of pre-drawn circuit boards.
Components are inserted by selecting and then dragging from the Parts Bin area at the upper right. Selected parts may be examined and configured using the Inspector area at the lower right. (Notice that the appearance of components is automatically updated, as with the 330Ω resistors in the above image.)
Connections are made by dragging wires between nodes, and these will initially appear as rubber-banded links in the other two views.
Fritzing does not simulate the circuit so you will need to build and test a real prototype to ensure your design actually works!
Schematic (Circuit Diagram) View
Components are initially randomly placed, but are dragged to the desired positions, oriented, and then linked by replacing each rubber-banded wire by a manually-drawn connection.
PCB (Printed Circuit Board) View
PCB view allows a permanent soldered design to be created based on the connections made in the Breadboard and Schematic views.
Fritzing's PCB feature includes options for manual and autorouted PCB design, and it is even possible to have your PCBs professionally manufactured and delivered for a small charge.
Selected Fritzing Resources
Fritzing is supplied as a folder structure inside a compressed ZIP file. Simply extract the file to a suitable location and then run the Fritzing application in the root folder. Windows users may find it convenient to place a shortcut to the Fritzing executable on the desktop.