Falstad is a free online circuit simulator. This JavaScript application is a fantastic learning tool for students of computer science and electronics. It’s particularly useful if you want to learn more about combinational logic and sequential logic. Falstad allows you to assemble electronic components into circuits then experiment with the way they respond to different inputs. You can also add so called 'scopes' to your circuit diagrams, which are essentially live timing diagrams. In addition, Falstad comes with several prebuilt circuits that you can experiment with. In this lesson you will see how to create a JK flip flop simulation.