A Simple Computer Algorithm for Selecting Appropriate Rs and Cs for a Specified Time Interval

In Part 3 you devised a graphical way to select a resistance value and a capacitance value to use in the interval timer so that a particular time interval is produced. This can be done using a computer, and a number of neat possibilities are possible.

The algorithm ("recipe") for the program is shown in the flow charts in Figure 32. The program uses existing files giving a list of resistors and capacitors available for use in the timer. Each component has a NAME and a VALUE in the file. These are read into memory. (The first value in each file is the number of components available in the file.) Next the user specifies the required time specifications, a nominal value and allowable error. The algorithm now searches every possible resistor and capacitor combination to determine if it meets the user's specification. If it does, then the resistor and capacitor names are printed out along with the nominal time interval the combination would produce. The user can then elect to try another specification or quit the program.

A listing of the program (DESIGN.FOR) and the resistor (R.DB) and capacitor (C.DB) files are given in Figures 33 and 34. There are 95 resistors and 24 capacitors in these databases, so there are 95x24=2280 combinations to inspect.

This is indeed a simple design program. Very elaborate software packages are available for electronic design.