A Free Digital Circuit Simulator - LogiSim

I have found that there are not many digital simulators that work well for digital circuits that operate on the gate level.

Now, when I say well, I also mean free. I'm a cheapskate and don't like to pay for software when a freeware, or open-source program is available to do the same thing as premium software.

Also, due to restrictions in the ebook on this site, I wanted something I could recommend to people that just want to simulate a digital circuit. Why should someone need to know the logic levels of certain components and how they aren't compatible with other suite components, when they simply need to check their digital circuit? Simulators can become a tangled web of frustration to a beginner, and even the seasoned veteran if ever he had to switch to a new software.

Thus, I found LogiSim, a free, open-source simulator for digital circuits! At first I was skeptical to run a *.exe from the internet, but I figured it was a reasonable risk and ran the application. I had a circuit I had wanted to simulate in working on the modulus counter article, and had the circuit up and running within minutes, a testament to the intuitive nature of the program. The only thing I had to look up was how to run the clock! It turns out, you must "poke" the clock, so you control the clock with the press of a button, no bounce included! (it is possible to automate the clock, but I like to watch the states change, so I do it manually)

So, you want to toggle a bit in a flip flop? Just click it! Want to display the state of an output(in case the color of the wire isn't sufficient for some reason)? throw an LED in there and connect, no current-limiting resistor required! There are a whole host of cool things in this program to get a firm grasp of digital electronics, everything from basic gates, to ROM & RAM, to a joystick(not quite sure what it does, but it's pretty cool to have!), buttons, and a keyboard module(which reads the actual keyboard on your computer!). So this thing can do some serious work!

Overall, I'd recommend it for anyone that needs gate-level digital circuit simulation, so, teachers, students, and anyone trying to get into digital electronics!

Here's an image of my simulation of a Mod-10 counter using JK flip flops, and no, this isn't the one I was talking about earlier. ;)

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