![]() (It has another option, the initial voltage, but we'll ignore that for now) The capacitor is described by Cname n+ n- value as you might expect. Next, there's the "motor" resistor described by Rname n+ n- value where value is the resistance, let's say 1Ω. A simple DC supply is described by Vname n+ n- value where n+ is the positive node, n- the negative node and value is the DC volts value. I spent about 2 hours trying to find out that I simply needed to number the ground node zero!! Note that the GND node must ALWAYS be node 0 or you will get errors like "Warning: singular matrix", "Warning: source stepping failed", "Warning: gmin stepping failed", "No convergence in DC analysis", and "failed to converge". Here's the circuit with the nodes labeled to make it easier to enter into a SPICE file. Let's start with a much simpler circuit we'll ditch both transistors and represent the motor as a simple resistor, tying it directly to 9V and GND. The description file lists each of the components, and what nodes the components are connected to. ![]() Then I have to convert that into a SPICE circuit description file. First I have to draw the old motor circuit. ![]() I found the following websites helpful, too: The MacSpice website has good documentation: I want to use modeling to analyze the existing circuit and to help me come up with a better design.īut first, let's talk about SPICE. Revisiting Pokey's Fan Motor Circuit: You may recall the crappy, last minute, motor driver circuit I threw together for Pokey, my firefighting robot. The tool remains text based, but with some menu wrappers for a few functions. You can model numerous devices and print and plot the results of the simulation. It can do transient analysis, steady-state, AC small signal analysis, DC transfer function analysis. SPICE, Simulation Program with Integrated-Circuit Emphasis, has been around for 30+ years and is still an industry standard for modeling circuits to see how they'll behave. ![]() The last couple days I've been learning how to use SPICE circuit simulation software and thought I'd share what I've learned. ![]()
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