1
\$\begingroup\$

I'm very new to the world of EE and PCB design.

A friend and I decided to make an LED matrix as an easy stepping stone into these areas. We breadboarded the entire circuit and copied the design over to fritzing and I worked on putting the PCB design together (shown below,) however, I had a few questions about connecting all my grounds.

I read that using a ground plane and vias to connect all the chip GNDs wouldn't hurt, and I was wondering how that is achieved. I'm not sure I entirely understand the ground fill as it leaves spacing around traces and leaves them disconnected. How would I specify which vias to attach to my GND plane?

Additionally, if someone much smarter could let me know if there's something horribly wrong on specifically the PCB design (all components and wiring has been tested and works correctly) it would be greatly appreciated as I'd like to actually order a PCB of this design and would like to do it with minimal iterations! (I ran the DRC and it said there were no issues it saw.)

ARDUINO_RGB_LED_MATRIX

\$\endgroup\$
  • \$\begingroup\$ What layout program are you using? Did you make a schematic? \$\endgroup\$ – The Photon Jun 13 '19 at 18:22
  • \$\begingroup\$ I am using Fritzing. I have a schematic view but it has not been organized at all. The wiring was done in the breadboard view \$\endgroup\$ – notaneemajor Jun 13 '19 at 18:23
  • 1
    \$\begingroup\$ This seems like an impossibly broad question. \$\endgroup\$ – scorpdaddy Jun 13 '19 at 18:24
  • \$\begingroup\$ I'm most concerned in how the GND fill works so I can connect my ICs GND together with VIAs \$\endgroup\$ – notaneemajor Jun 13 '19 at 18:25
  • 1
    \$\begingroup\$ I would recommend against using fritzing. It has limitations that you may not run into right away, but when you do hit them you will pretty much be forced to learn a new program. Why learn a bad program, then have to start all over and learn a better one when you can start with the better one. They both cost the same (free.) \$\endgroup\$ – JRE Jun 13 '19 at 18:43
2
\$\begingroup\$

You won't need vias to connect your IC grounds to a ground plane. You are using through hole parts. The holes are plated, and basically they are oversized vias. Any pin that connects to ground would automatically be connected to the ground plane - provided that you manage to define the copper area as a ground plane.

As for creating a ground plane in fritzing, that would seem to be fairly easy.

From the fritzing forums:

To create the ground fill you just need to right click on a connector or pad that is part of your V- (GND) net and select set as ground fill seed. If you have more than one circuit with separate V- (GND) nets then you will need to set at least one seed for each net. After that make sure both layers are set as clickable (or which ever layer you want the ground fill on if you only want it on one) then go to the Routing menu > Ground Fill > Ground Fill (Top and Bottom).


Mmmpf. Forgot the part about the board layout.

You've got traces front and back on that board. That can chop your ground plane into little, unconnected pieces. Try to route everything on the top side, and only use the bottom for short jumpers to get around crossovers on the top.

The layout itself looks reasonable for what you are doing - I don't see anything that looks particularly tricky.

What I do notice, though, is that you have no decoupling capacitors for your ICs.

You might get away without them, but maybe not.

You should add small capacitors (typically 100nF) at the power pins to each IC. I mean right at the IC. Shortest leads possible, shortest traces possible. Each time a digital IC switches state, it draws a really short pulse of current. If they all do that at once, then it can cause the voltage to each IC to drop - and then the ICs get stupid ideas like freezing or giving random outputs. The little capacitors catch the current spikes and keep the voltage steady.

\$\endgroup\$
  • \$\begingroup\$ Thanks for the help. One last question, what would be the advantage of separate GND nets? Are there cases where isolated GNDs are needed? \$\endgroup\$ – notaneemajor Jun 13 '19 at 18:55
  • \$\begingroup\$ You probably shouldn't use separate ground planes without knowing for darned certain you need them. What can happen with the nets is that a connector or an IC defines a pin as ground, but it has a different net name. You need to join those different ground nets together. If you connect them with a trace, then that happens automatically. If you try to connect them only through the ground plane, you will have to do it as described in the forum link. \$\endgroup\$ – JRE Jun 13 '19 at 19:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.