Electrical Rules Check (ERC)

By Dan Aukes

Introduction

In the last tutorial you created a schematic. But is it any good? The electrical rules check, or ERC, is a useful way to debug your circuit. This example tutorial takes you through the process of finding and eliminating circuit design errors.

Resources

Steps

  1. Open up the adjustable voltage regulator circuit from the previous tutorial.

    Prior Schematic
    Prior Schematic

  2. Go to inspect –> “electrical rules checker” in the menu.

    Open ERC
    Open ERC

  3. Select run and inspect the results. There should be two errors.

    Two Errors
    Two Errors

    These errors indicate that the 12V and ground power connections are not connected to a source. Which is true! We forgot to add an external power connector to the board design, as in power from the wall or from an off-board battery!

  4. These errors can be resolved by adding a power connector. Select add part

    Add Part
    Add Part

  5. Search for “screw terminal” and select the 1x2 version (one row, two positions).

    Select a screw terminal
    Select a screw terminal

  6. Place the screw terminal and wire it up

    Place part
    Place part

    Wire it
    Wire it

  7. Because the 12v and ground symbols are “power ports”, you can use as many of them as you want in your schematic, because they all signify the same thing, rather than a copy. So for the purposes of ERC, place a separate ground symbol (the same symbol as you used before) near the second pin of the screw terminal and wire it up.

    Add GND
    Add GND

    Wire GND
    Wire GND

  8. Run Annotations (assign reference designators)

    Run Annotations
    Run Annotations

  9. Run ERC again

    Open ERC
    Open ERC

    Run ERC
    Run ERC

    See Errors
    See Errors

    Why are there still errors? The screw terminal pins are “passive” pins; they don’t indicate a power connection. To solve this you must explicitly state that pins 1 and 2 of the screw terminal are power outputs.

  10. Double click on the screw terminal

    Open Symbol Properties
    Open Symbol Properties

    1. Click Edit Symbol

      Editing a symbol of a built-in library directly from within a schematic will only impact that schematic; it will not be propagated back to the library.

    2. Change pin 1 and 2 to “power output” types

      Select Power Output
      Select Power Output

    3. Save and close the symbol editor window.

      Save Symbol
      Save Symbol

  11. Re-run ERC one last time

    One Warning
    One Warning

    The one remaining warning indicates that you have locally edited a symbol within the schematic. This was intentional in our case, and can be ignored.

Delete Markers

You can delete the markers (little arrows in your schematic) generated by ERC by opening up the ERC tool and selecting the “delete markers” button

Delete Markers
Delete Markers