Questions regarding power symbols (How to make two non connected 3v3 systems)


#1

Hi,
I want to use two voltage regulators, with separate track paths. Kicad is showing both 3.3V as connected. Is there a way round this please?

EDIT: I’m not sure if this is the correct way, but I had two 3.3V power points. I’ve now removed one and the tracks are separate now.
C.


Getting up to date
#2

If follow up questions have very little to do with the original content, make a new topic as you will get more help that way. (I split it because of that)


About your question:

A power symbol (i assume this is what you call a “power point”) is nothing else then a fancy global label. So any such label with the same name (in this case +3v3) will be connected over all hierarchical sheets.
If you do not want to have two such things connected you have a few options.

Option 1 (for small circuits):
Use no labels at all. Just directly connect everything


Option 2 (the kind of simple way):
Use global labels instead of power symbols. Name the labels differently for both your 3v3 systems. (Example would be: +3v3_MCU, +3v3_Analog; Or simply +3v3_1, +3v3_2 depending on your exact usecase and your preferences)

Option 3 (Option 2 but with custom power symbols):
Creating a power symbol is not really hard but at the same time not straight forward either.
I would create a project local symbol library for creating such a specialized power symbol.

A power symbol consists of one invisible power input pin. (This is the thing that creates the label) The pin name is what will become the label name.
In addition it normally has some grapical elements that help the user identify it (completely optional but highly suggested)
The symbol reference must start with “#” and you should set the “is a power symbol” flag in the symbol properties. (The “#” tells kicad not to include this symbol in the BOM and not to try to find a footprint for it)
It is suggested to use the same symbol name as pin name. (Makes it easier for the user to identify which label will be created. Again optional but highly suggested)

Option 3a (use power symbols already in the lib)
If you find two different power symbols in the lib that fit your needs (Names are different and you can work with these names) then you can use them instead of designing your own power symbols.


A bit more sophisticated would be to design your schematic such that you can use hierarchical design. In such a case i would not use any global labels at all and accomplish everything with local labels or hierarchical pins.


#3

Hi R,
Ok thanks.

Actually, I find it difficult to learn what may seem quite easy for you. I normally press buttons like a monkey till I either get the result I want or have to stop and go through the instructions, then usually forget them.

I think monkeying around isn’t very efficient, but some of us have to use different methods.

I’ve mainly done my circuit, apart from the routing, and printed out an SVG showing everything will fit. I’m not sure if you would call it large or small, but it has 47 components, including two PICs. Anyway, considering I’m now using the Kicad methods, I find it fairly intuitive.
Cheers, C.


#4

Appear that in your case is better use different labels.
I had this problem once. I used +5V inside a hierarchical sheet that replicated 16 times. I did the layout of this hierarchical part, replicate it and ignored on DRC. It was not the beautiful solution, because despite others EDAs, KiCad doesn’t have a option to make the power page-local (https://bugs.launchpad.net/kicad/+bug/1728250).
But, if your problem is “same voltage level from different regulators to different proposes” could be better and better to read the schematic for other guy, use different names.
Give a “+e” on the power symbol, edit it with the different names and save on the project local library.


#5

Well that is what hierarchical pins and local labels are there for.


#6

Hi,
I note the points above.

I have made an error and need to delete a GND plane I’ve set. I’ve tried both top and bottom layer, selected ZONE, then delete, but the Zone is still there.
Is this my error or a Kicad fault?

**EDIT: I selected everything except the ZONE and moved it, leaving the ZONE behind, then deleted it. **

C.


#7

KiCad doesn’t automatically recalculate filled zones when editing board elements (drawing traces, moving components, and even deleting zones. You need to force it by pressing B to recalculate (refill) the zones. This will also clear up leftover fill from deleted zones.


#8

Hi S,
Ok, thanks, I think I understand.

EDIT: AH the B on the keyboard! It worked :slight_smile: While looking for the B, I found the measure tool. Good!

C


#9

Hi,
If possible I want to add switchable tracks (2x PICs = 2x switchable tracks) between the Regulators and the PICs, on the reverse of the board.

There is a GND plane covering the reverse of the board.

I assume I add a VIA next to the REG power pad and another next to the PIC VDD, then add 2x pads in the track for the switch.

How is this done please?
C.


#10

What is a “switchable track”?


#11

Hi B,
On the PCB are two PICs, which will be programmed in circuit. I need to be able to switch each PIC ON/OFF for programming individually.
C.


#12

If I understand you correctly, you could either use a jumper if you are only going to program the PIC(s) occasionally. Alternatively, you could use a MOSFET on the RESET pin. When the MCU is running, the RESET line is pulled up to 3.3V but the programmer will pull it low to enter programming mode. You could use a cheap 2n7000 or equivalent to achieve this.


#13

Hi J,
I presume you mean MCLR? (Pickit3)
If so then I have a button connected to both MCLR pins. If I split them and add another button, 1x for each. Will this do?
C.


#14

So you have two PICS connected to one set of programming lines?

I might use jumpers, but need to check if a PIC is “reverse powered” it might still get enough power to go into programming mode.

The standard way is to have two sets of programming pins, but you might be able to find a suitable pin to put a jumper on, MCLR, or data in or whatever.


#15

Hi,

I’ll add a separate programming connector.

C.


#16

I think, there is a fundamental issue with your idea. When you only disconnect Vcc or Vdd supply to the PIC, it may not shutdown as you expected. Usually the PIC that got disconnect will pull a lot of current from all the IOs connect to it. Also, using a zero ohm, 0603, or Jumper would doing the temperate ON/OFF for you (But again, you should not do at Vdd or Vcc pins).