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Posh, Sporty or Scary?! - Electronics with a Touch of Spice

For many years now, I’ve been a firm advocate of simulation software. I’m long enough in the tooth to remember when a deck of SPICE cards meant exactly that. In fact my first SPICE run as a designer was done with punched tape at about the same time as those new fangled TTL chips (not even LS TTL) were coming onto the market.

But tempus fugits as it always does and things are (thankfully) a whole lot more user friendly than they were. Back then rerunning a speculative SPICE analysis meant filling out a form, getting the punch card people to do their thing, waiting until the next time slot came on the mainframe (each Tuesday for my college course!) and then getting a printout back with the results. Typically a week turnaround!!!

Nowadays I like to use LTSpice (aka SwitcherCAD  III) from Linear Technology for the majority of my analogue simulations. This is a free download application written by Mike Engelhardt and downloadable from http://www.linear.com/designtools/software/ltspice.jsp. It has an excellent User Forum at http://tech.groups.yahoo.com/group/LTspice/ where you can almost always find someone to answer your questions, and that might even be Mike Engelhardt himself. It’s not always 100% intuitive and does differ in detail from other SPICEs, but I love it.

Now it’s a snap to sweep a parameter to find the optimum value for a specific condition, run a Monte Carlo analysis to see when (and that is when, not if !) production tolerances are going to hit you, or even to solve the odd differential equation to save you pulling out Matlab or Mathcad.

But caveat emptor! As with all modelling it’s essential to remember the immortal lines from Monty Python and the Holy Grail……..


LANCELOT:     Look, my liege!
ARTHUR:      Camelot!
GALAHAD:      Camelot!
LANCELOT:     Camelot!
PATSY:          It's only a model.


...and your modelling is only as good as your assumptions. Always check results with a few real life measurements as a sanity check!

By Ray

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