Every now and again the digital design engineer has to completely leave his (or her) comfort zone and enter the occult of analog design engineers. It is in this world that digital design engineers, used to making yes or no binary decisions, are presented with a multiple of answers all of which, or none, may be correct. It is in this blurry and murky world that any type of help, to corroborate a design, is most welcome.
As part of designing a servo controller board for the 17 DOF Robot (Using FPGAs) Project I had to enter such a world. However, rather than approach the design with Wigi (Ouija) board to hand, to confirm my results, I simulated the circuit design using the electronic equivalent or a Software Program with Integrated Circuit Emphasis, otherwise known as SPICE. The installation of LTspice IV on Mac OS X (Yosemite 10.10) is the subject of this blog post.
There are probably many PSPICE type simulation programs available for Mac OS X. However, since I have used LTspice IV successfully in the past, to perform simulations on a Windows platform, I was quite excited to learn of its availability for Mac OS X (version 10.7+).
According to Wikipedia, LTspice IV is a freeware computer software implementing a SPICE simulator of electronic circuits produced by Linear Technology. It provides a schematic capture and waveform viewer.
Firstly, one should navigate to Linear Technology's website and from there onto the design tools page (http://www.linear.com/designtools/software/), a screenshot of the page is shown above. In the bottom right-hand corner you should see the option to download LTspice IV for Mac OS X 10.7+. Clicking or double clicking on the option downloads a 51.2 MB file to your download area, as can be seen in the upper half of the Figure below.
Double clicking on the downloaded LTspice IV.dmg icons mounts a LTspice installation, as a device. This device appears on the screen as a folder with the content shown in the lower part of the image in in the Figure above. If the open folder does not appear automatically one needs to double click on the LTspice Installaion under devices. The green finger pointing hand is an instruction to drag the LTspice.app to what appears to be a shortcut to the Applications folder.
After completing the folder dragging process I had installed LTspice. Again, like our previous software installations, this was a fairly painless process. To actually use the application, after installation, one needs to navigate to the Launchpad and double click on the LTspice icon, shown as image (A) in the Figure above.
The first time you attempt to run the application you will be presented with the pop-up message box seen in the Figure above, image (B). "LTspice is an application downloaded from the Internet. Are you sure you want to open it? If you are sure that this application is "legit" then you can click on the "Open" button, where you will be presented with the dialog presented in image (C). That is it really.
Once the application is running you can create a new schematic and populate with components by Right-clicking on the schematic and navigating to Draft->Component. The Figure above shows a quick component test\check I performed for NPN transistors, an opto-coupler and a Low Dropout (LDO) voltage regulator. If I want to actually run a simulation with a 2N2222 NPN transistor and the HCPL-2730 opto-coupler I would need to get the SPICE model, which implement these components, from the respective manufacturer's website and import them into LTspice. An exercise that I should treat in a separate blog post.
Just like with any SPICE simulator you can place probes on the nets and view the waveform, as in the Figure above. That's it for now, you can follow our adventures in the analog world and SPICE by regularly tuning into our blog posts. Cheerio!