****************************************************************** * * * SNAP - Small Nodal Analysis Program * * * ****************************************************************** Written by: Jerry Fitzpatrick 636 Cherrywood Drive Wheeling, Illinois 60090 6/4/88 Version 2.1 released Introduction ------------ SNAP is a linear electronic circuit analysis program that is somewhat like SPICE. To use SNAP, you create a text file describing the circuit you wish to analyze. This "network" file is a collection of component types, labels, values, and node numbers which is processed to create a runnable SNAP program. The programs you use are: PRESNAP - converts the network file into a runnable SNAP file SNAP - creates a custom screen and window, allowing you to read in a SNAP file and perform DC or AC analysis and output data to the console, printer, a file, or built-in plotter. This version of SNAP supports up to 50 nodes, 100 components, and 50 output variables. SNAP is quite fast: it can solve a 7-node circuit for 100 different frequencies and plot 500 points, all in 30 seconds (refer to the AC example). Using SNAP ---------- To use SNAP, follow these steps using the CLI: 1) Create a network file using a text editor. I recommend Rick Stiles' UEDIT (hint, hint) but ED and other ones will do. The name of this file must end in '.net'. 2) Compile the network file using PRESNAP. This will create a new file by the same name, but with the extension '.snp'. DO NOT specify the extension in the file name. That is: use, PRESNAP my_circuit NOT, PRESNAP my_circuit.net If PRESNAP finds errors in the network file, it will not create an output file. Instead it puts out error information in a file named 'snap.err'. 3) Invoke SNAP by typing 'SNAP' on the command line. Select OPEN from the project menu and, at the requester, enter the file name. As with the network file, DO NOT specify the extension. Network Component Templates --------------------------- There are eleven component types in SNAP. Each one is denoted by a unique three-letter mnemonic (such as RES for resistor). Each component has its own set of parameters that is needed, as shown below: Resistor RES Label N+ N- Value Capacitor CAP Label N+ N- Value Inductor IND Label N+ N- Value DC Voltage Source DCV Label N+ N- Value AC Voltage Source ACV Label N+ N- Value DC Current Source DCI Label N+ N- Value AC Current Source ACI Label N+ N- Value Current-Controlled Voltage Source CVS Label N+ N- Branch Value Current-Controlled Current Source CCS Label N+ N- Branch Value Voltage-Controlled Voltage Source VVS Label N+ N- NC+ NC- Value Voltage-Controlled Current Source VCS Label N+ N- NC+ NC- Value N+ = positive node N- = negative node NC+ = positive control node NC- = negative control node Label = component label, up to eight characters Branch = the label of the controlling branch Value = component value (in ohms, farads, etc.) Output Templates ---------------- There are ten output types in SNAP: five for current and five for voltage. Each one is denoted by a unique two-letter mnemonic following a period, as described below: Voltage (in volts unless otherwise specified) Real Component .VR N1-N2 ... Imaginary Component .VI N1-N2 ... Magnitude .VM N1-N2 ... Phase (in degrees) .VP N1-N2 ... Magnitude (in decibels) .VB N1-N2 ... Current (in amps unless otherwise specified) Real Component .IR Branch ... Imaginary Component .II Branch ... Magnitude .IM Branch ... Phase (in degrees) .IP Branch ... Magnitude (in decibels) .IB Branch ... N1-N2 = voltage difference between nodes N1 and N2 (the '-N2' may be omitted if you want voltage with respect to ground) Branch = current through the specified branch (only resistors, capacitors, and inductors are allowed here) **************************** Menus ******************************* Project ------- About Produces a small advertisement for SNAP. Open Brings up a requester for you to enter the name of the SNAP file to be opened. Once opened, the file name is displayed in the title bar at the top of the screen. Quit Exit from SNAP. Analysis -------- Type Selects analysis type, AC or DC. If you choose AC, you will be prompted for a range of frequencies and the number of points to calculate. Warning: hundreds of points can take quite a while to display or print. Plotting is usually more appropriate in these cases. Scale Selects the type of scale to use for AC calculations, logarithmic or linear. For Bode plots, use the LOG scale. For better plotting accuracy over short frequency ranges, use the LIN scale. Start Starts the analysis. If the calculations are likely to take more than fifteen seconds, a requester will ask you to verify whether you want to proceed. Output ------ Console Selects the console as output. Keep in mind that your outputs will scroll off the screen if they run longer than about 22 lines (inc. the SNAP header). Printer Selects the printer as output. Plotter Selects the plotter as output and activates the PLOTTER menu. The first five outputs in your network file are plotted. The plots are automatically scaled based on the minimum and maximum values of all the outputs. LOG plots can span a maximum of three decades. The plots are color-coded in the order (1) ORANGE, (2) BLUE, (3) YELLOW, (4) VIOLET, and (5) GREEN. File Selects a file as output. A requester lets you choose the name for the file. Plotter ------- Redraw Redraws the plotter output on the screen. This is also useful for plotting the calculations after printing them out, without re-starting. Title Lets you enter a text title for the plot. The title is displayed centered at the top of the plot. Save Saves the plot screen to a file named 'snap.plt'. This file is in IFF format so you modify the plot with DeluxePaint or other such programs.