Efficiency of any electronic circuits can always be improved by simulating it before actually building to pcb or general board. The best method to check a design in electronics is to use a circuit simulator and make a simple model of it to see how it works before assembling the real circuit. Electronic circuit simulation tools use mathematical models to replicate the behavior of an actual electronic device or circuit. Here are some freeware tools that will allow you to replicate the behaviour of an actual electronic circuit. All these circuit simulators suggested here are free to download.
1. Electric 8
It's an open-source electronic design automation (EDA) system that can handle many forms of circuit design and simulation. This software features include custom IC layout, schematic capture (digital and analogue), and textual languages such as VHDL and Verilog. The Electric VLSI design system is a highly flexible system that can handle many different types of electronic circuit design. Layout is done by placing and wiring electrical components. Electric comes with a built-in 12-state switch-level simulator, called ALS. The simulator displays waveforms in a separate window and lets users cross-probe from either the waveform or the circuit window.
Logisim is an opensource educational tool for designing and simulating digital logic circuits. It has the capacity to build larger circuits from smaller sub-circuits, and to draw bundles of wires with a single mouse drag, Logisim can be used to design and simulate entire CPUs for educational purposes. Its simple user interface and simulation of circuits as you build them, make it a tool that is simple enough to learn the most basic concepts of logic circuits.
Ngspice is a mixed-level/mixed-signal freeware open source circuit simulator. Its code is based on three software packages: Spice3f5, Cider1b1 and Xspice. Ngspice is part of gEDA project--a full GPL'd suite of electronic design automation tools.
4. Simulo v2.5
Simulo is a digital circuit. It's easy to use and is designed for students and hobbyists. This program is made by Benjamin Gentner.
Note: Requires .NET 3.5
Quite universal circuit simulator (Qucs) is an open source electronics circuit simulator software mainly for students. The software aims to support all kinds of circuit simulation types, e.g. DC, AC, S-parameter, transient, noise and harmonic balance analysis. Pure VLSI digital simulations are also supported using VHDL and/or Verilog.