Rombos A Two Resistor Series/Parallel Combination Calculator



-          13 March 2007 : First Edition


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Resistors are usually manufactured according to a specific set of resistance values. Two common value sets are the E24 set of values and the E96 set of values. While it is possible to find resistors manufactured to a wider set of values, it may involve a custom order and need a longer lead time.

Placing two resistors in series or parallel using the more common set of values is one way to create a resistance value closer to the desired value.

This program can help in the selection process: by selecting the desired target value, the allowed error in percentage, and the connection type, the program lists the combinations which are within these parameters.



-         Series or parallel selection.

-         Use E24 or E24+E96 series values.

-         Adjustable error allowance 0% to 10%

-         Import a list of target values for batch mode use.

-         Results are listed in a scrollable window.

-         Date and time and software version listed in window.

-         Select for copy/paste operations supported.

-         Window results can be written to a log file.

-         Resistor power is listed for a given voltage.

-         A single win32 executable. Does not install or require any libraries or updates.




Figure 1 Rombo Screenshot


Future Work


-         more intelligent combination searches, especially for E96 searches. A search of a high resistance values can produce several combinations like 100000 and 10, 100000 and 12 , etc.

-         for parallel mode, an open is listed as 9999999. Could be done better.

-         settable decade ranges. Would be especially useful to do this for E24 and E96 separately.

-         importing a custom set of available resistor values could be useful to do the search

-         listing all the actual resistor values used in the program would be good practice.

-         add aging and manufacturing tolerance calculations.

-         a Linux version if demand is there. GUI is FLTK based.