iCircuit

Its advanced simulation engine can handle both analog and digital circuits and features realtime always-on analysis. It is the perfect companion to students, hobbyists, and engineers. You use it as you would any CAD program: you add elements, connect them together, and set their properties. But iCircuit is unlike other CAD programs because it is always simulating. It's just like working with the real circuit. You do not stop to take a measurement or spend a lot of time configuring reports. Instead, you just play with the circuit as you normally would, with the power on! There are over 30 elements you can use to build your circuits. The app has everything from simple resistors, to switches, to MOSFETs, to digital gates. The app features a multimeter that you use to probe around the circuit to instantly read voltages and currents. If you want to see how a value changes over time, then you can add values to the built-in oscilloscope. The scope can simultaneously track many signals over time and features a touch interface to control the total time displayed and stacked and unstacked modes to easily compare signals.

Supported elements include:

Signal generators, Voltage sources, and Current sources Resistors, Capacitors, and inductors Manual SPST/SPDT Switches, and SPST/SPDT relays Diodes, BJ Transistors, and MOSFETs Speakers, Buzzers, and LEDs ADCs, and DACs Logic gates: AND, OR, NAND, NOR, XOR JK and D Flip-flops