I’m new to KiCAD. I have become relatively proficient with Eeschema. My question is regarding adding bypass cap’s to my circuit. The IC generally have the power pins hidden. So without turning on these power pins, how do I add bypass cap’s? Thanks Mike
I’d worry more about how you connect power…
I’ve used the Power Flag to connect power to various items. Mike
so just drop some caps between there and GND?
The problem is that I want to place a bypass cap at the power pin of each IC. How will KiCAD know where to place the footprints of the bypass cap? Mike
it doesn’t. you do the layout.
I’m not getting it. If I place a dozen bypass caps and connect them to the power flags. Then when I go to make the layout I have to move them to where I want? Mike
yup you’ve got it right
OK, thanks. I’ll give it a try. Mike
What version of KiCad are you using, and which library are you pulling your ICs from? Hidden power pins for ICs no longer conform to the standards for the KiCad libraries. AFAIR in v5 most of the IC libraries (there may be 1 or 2 that haven’t been updated yet) have the power pins as an additional gate (called “Unit” in KiCad) symbol for the IC. If you don’t place that gate then your ICs won’t be powered when you send your netlist to PCBNew. (Unfortunately, the ERC in EESchema doesn’t warn about unplaced gates…)
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Sadly a few of the logic libs still use hidden power pins in the official lib as nobody cares enough about them to fix this.
I just updated to 5.1.4 . The library is an old custom library I made using 5.0.4 . But my library skills are not the best. My custom library has old Intel IC’s in it. Items like 8251 Uarts, 8080 CPU etal. I had defined the powerpins, but after some reading I made them invisible. Was that a mistake? Mike
I just looked at a 74xx gate and see that there is an extra gate soto speak that has the power pins. I suppose that I should modify my library items to have this? Mike
Many of us are convinced that this practice has more disadvantages than benefits. Either approach is workable, and your choice may be controlled by the habits, fears, inertia, and prejudice within the organization where you work. Favoring one approach over the other will not affect your eternal destiny.
Dale
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Currently, the consensus favors this approach. The implicit assumption is that a bunch of these “power units” will be collected in some out-of-the-way corner of a schematic, and surrounded by bypass capacitors (and possibly other power conditioning circuitry). Segregating these components like this may encourage us to mentally associate them, and consequently follow good layout practices when we place them on a layout.
Your personal library is likely to be equally effective whether you adopt this practice or not. Off hand, I don’t recall whether the KLC (“KiCAD Library Conventions”) explicitly permit hidden power pins, or discourage the practice, or define it as “Non-Compliant”, or are silent on the matter.
Dale
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Hidden power pins are strictly prohibited https://kicad.org/libraries/klc/S4.6/ (exception power symbols but well they are the reason why this hack exists in the first place)
At like that IC power pins I use 100n and then 1k ferryte bead to VCC. If I had hidden power pins I would be not able to do that at schematic. For standard digital ICs I would accept separate symbol just to connect power, but for more complicated ICs I prefere to see just at that IC and not somewhere in sheet corner how its power is filtered. About 15 years ago I tried to make VCC and GND pins in pairs to show at schematic which capacitor is at which VCC/GND pair but I changed my mind and now I have all VCC pins at symbol top and all GND at bottom.
OK, I restored the power pins and will use them for my bypass cap’s. Thanks for the help Mike
I just want to add that I like the approach of the OPamp library better (Power pins that can be “attached” where you expect them on the OPamps) rather than the logic gate library (Power pins that sit on a function-less colored box). I like having the pins on one item from the IC. But I can live with it as it is now.
I’m willing to give the ‘Unit’ idea a try. It’s similar to what I did in the past anyway.
What I use to do when I built a schematic was distribute the caps very near the IC they were intended for. Then when I annotated they would carry a part number that made sense considering that they would be close to the IC. After the PCB was verified, and a production run started, I’d move the caps down to a corner of the schematic with notations that they were bypass caps distributed near ICs and devices. A complete explanation would be on the ECN but it would be a ‘Memo’ type so the revision level wouldn’t change. (My schematics, PCBs and all the other components of a design carried the same Rev level).
The only issue I’d have with the Units idea is that sometimes room on a drawing is tight.
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