topic Re: PCB design check and one GND airwire not disappearing in EAGLE Forum

PCB design check and one GND airwire not disappearing

alexander.wrede — Thu, 21 Nov 2019 10:31:31 GMT

Hello,

I'm creating an Arduino driven dew controller for my telescope and have created enclosed layout.

(heating the telescope mirror when its temperature gets to close to dew point)

Can the pros kindly have a look to the .brd and suggest improvements to a newbee like me.

There is also one GND airwire (bottom right) not disappearing, despite its all connected.

Any hints on that or just leave it?

Thanks and kind regards,

Alex

Re: PCB design check and one GND airwire not disappearing

one-of-the-robs — Thu, 21 Nov 2019 11:05:41 GMT

@alexander.wrede wrote:

Hello,

I'm creating an Arduino driven dew controller for my telescope and have created enclosed layout.

(heating the telescope mirror when its temperature gets to close to dew point)

Can the pros kindly have a look to the .brd and suggest improvements to a newbee like me.

Well, they might have a look if you actually attached it 🤔 You probably need to ZIP them to get past the forum's filter.

@alexander.wrede wrote:

There is also one GND airwire (bottom right) not disappearing, despite its all connected.

Any hints on that or just leave it?

Nearly every time someone says this, they've not looked closely enough at the layout and missed the fact that part of their ground plane is not connected to the rest of it. I'm guessing you haven't explicitly routed your ground signals and have just relied on the polygon fill. You should never rely on that. Never. ALWAYS ROUTE YOUR GROUNDS, to make sure they're still routed when you "just quickly add one more mounting hole". The polygon fill cannot be trusted to maintain connections because that's just not what it's for.

Re: PCB design check and one GND airwire not disappearing

alexander.wrede — Thu, 21 Nov 2019 12:27:07 GMT

Thanks for your answers.

New try, enclosed as a ZIP file.

Have in meantime manually routed the GND wires before creating a polygon but same issue.

I have insert a "zero ohm" transistor to use as a bridge but the airwire goes through the resistor, strange enough.

Re: PCB design check and one GND airwire not disappearing

one-of-the-robs — Thu, 21 Nov 2019 13:18:56 GMT

You have drawn that 0-ohm resistor with both ends connected to the same net - in this case "GND". When you do that, Eagle knows that both ends are the same net and expects there to be a PCB connection between the two ends. After all, that's what you've told it to do! If you want two different nets to be connected together at one point only, a 0R link is one way to do that, but they must be different nets for it to make any sense. If they're the same net, they need to be connected somwhere on the copper.

My preferred way to fix the "I can't route my ground completely on a single-sided board" issue is to draw it as double-sided but with very limited use of the top copper. In your case, I would delete R7 from the schematic - it's doing no good there - and instead route the airwire from X1/X7 to pin 14 of the Arduinowith a short hop to the top copper layer where R7 currently is. Make the board as if it's only got the bottom - i.e. just ignore the top copper - and insert a wire link where the top copper track is. You will want to make the vias big enough to look like pads, but that's no problem.

Other minor observations:

- you don't say how you intend to get this board made. My immediate thought when looking at a single-sided, through-hole-only design is that it might be home etched. This may be because most such boards that I design are for teaching 12-year-olds. Anyway, if it is for home etch, I'd avoid running tracks between pins of the DIL socket. The trace N$15 to X4 from pin 9 could be routed between N$16 and N$18 then taken round X4 pin 4. The GND trace from X5 can route directly to pin 19 if N$17 is hooked round X5 pin 3 (and maybe move R6 left a bit to clean it up).

- I don't see any decoupling capacitors. If all you were doing was breaking out a module to easier connectors, that would be fine, but there seems to be a voltage regulator (IC1), which should definitely have them.

(I actually think, if you rotate IC1 and relocate X6, X2 and X7, you may be able to avoid that wire link on your ground net).

Re: PCB design check and one GND airwire not disappearing

alexander.wrede — Thu, 21 Nov 2019 15:45:13 GMT

Reworked it.

Added capacitors, a diode and two wire links. Have kept the wires from going around the DIL pins.

Enclosed the updated board. For a home etch I dont have the equipment and not sure I m able to do it well enough also with the fine drilling.

Will let make two pieces somewhere as still much cheaper than buying a commercial dew controller.

Kind regards,

Alex

Re: PCB design check and one GND airwire not disappearing

one-of-the-robs — Thu, 21 Nov 2019 17:00:15 GMT

In the absence of the schematic, and, indeed, the full system overview, it's hard to say whether this is actually wrong, but...

The KK header named "SW" has only one pin connected. This looks dubious, especially as "SW" (without a number, even) would be an unusual name for a pin header. Is the diode intended as a reverse connect protection? If so, surely it should go between the supply connector (X7?) and the regulator input (N$19)

Re: PCB design check and one GND airwire not disappearing

alexander.wrede — Thu, 21 Nov 2019 17:45:53 GMT

SW stands for a switch which I am having here already.

In fact its a DC connector and the switch put together. Also for the display, temperature and humidity sensors I m just putting connectors to attach them to the board.

The heat strip is regulated via a small MOSFET breakout board for which are two connectors on the board, X7 as the 12V connector for the MOSFET, X6 for the signal line and for an LED when the heating strip is on.

Enclosed the schematics beside the board.

Re: PCB design check and one GND airwire not disappearing

one-of-the-robs — Thu, 21 Nov 2019 20:37:39 GMT

Well, it's your design so it's up to you how you do it. However, if it were mine:

- I would group the power and signal for the MOSFET board onto a single connector

- I would group power and ground input onto a single connector, probably without the link on a pair of pins, unless you want to use that to allow direct connections. What I mean is, either

1) a 2-pin connector with a switch in the wiring to the battery, or

2) a 4-pin connector so that the battery connects to pins 1 & 2 and the switch between pins 3 & 4

- I would tidy up the schematic a bit. Avoid diagonal lines, name the nets, use supply symbols to avoid so many explicit nets.

What you have should work, though.

Re: PCB design check and one GND airwire not disappearing

alexander.wrede — Fri, 22 Nov 2019 08:54:23 GMT

Good morning,

based on your input have redrawn the schematics and modified the board.

Looks both much better now.

Thanks a lot !

Alex