Electrical Rules check (ERC):
After creating the schematic and annotating circuit, it is necessary to check whether the circuit has any electrical errors. Like, if Nets are not connected properly, the input is not connected to the input pin, Vcc and GND shorted anywhere in the circuit, or any pin electrical type not selected properly, etc. All these are electrical error types. If we have made any such mistake in schematic, and if we are not performing any ERC, then after completing the PCB we cannot get the desired result from the circuit. So, ERC is mandatory.
: The Electrical Rules Check (ERC) tool performs an automatic check of the schematic. The ERC checks for any errors in your sheet, such as unconnected pins, unconnected hierarchical symbols, shorted outputs, etc.
To perform ERC on a schematic, we have to click on the ERC icon . If the circuit has no errors, then it shows Errors and warnings as zero. On the other hand, if it finds any errors it will show us the number of errors and warnings.
Fig. 1: Screenshot of Electrical Rules Checker Window on KIcad
Fig. 2: Screenshot of Electrical Rules Checker Window on KIcad
If ERC finds any errors or warnings it gives the details like error at which pin, along with an appropriate reason. In schematic also it will show a green arrow mark to indicate the error.
Fig. 3: Screenshot of a Warning or Error Detected by ERC on KIcad
So, there is no need to struggle in order to find out where the error is present and why. But we have to find the solution.
I completed a circuit, and got 6 warnings but there were no errors in ERC report. In these warnings, first two warnings included, pins not connected. Actually, I did not connect pin 5, 6 of the Component DS1 properly. Remaining warnings were regarding not connected and not driven pin warnings. If we look at the green arrows in the schematic, we can realize the mistakes.
Actually, I had not connected LCD 4,5,6, pins properly. I placed Net labels but didn’t connect them properly; So I adjusted labels and nets, and made connections properly. Again I performed ERC. Once again, I got the same errors. After observing schematic thoroughly, I found that LCD 4,5,6 pins were not connected to microcontroller 10,11,12 pins. Instead, I had placed “not connect” at microcontroller 10, 11, 12 pins. So to solve this, I placed Nets with suitable connecting labels to LCD. Once again I performed ERC. This time, I got only two warnings.
Fig. 4: Screenshot of a Warning or Error Detected by ERC on KIcad
To solve these two warnings I spent a lot of time. These were ‘not driven’ warnings. Finally, I found the solution. The mistake was that while creating an ADC0804 component in library editor, I had selected the wrong electrical type of the “V-in” pin. I had selected V-in pin as power input, but it is power output. After adjusting this, I got one warning in ERC report i.e. LCD 2nd pin was not connected to pot. So by giving Net and suitable label I solved that as well. Finally, in ERC report, I got “0” warnings and “0” errors.
In ERC report window, the optional panel allows us to configure connectivity rules to define electrical conditions, warnings, and check. If we need any modifications in this panel we can do that. In this, we can see that squares are arranged in the matrix. Each square indicates that pin type and pin electrical type. If we need any changes in present configuration, we can do so by clicking on the desired square in the matrix.
Fig. 5: Screenshot of ERC Configuration in KIcad
Filed Under: Tutorials