Some general questions about routing

[Solenoid]

I'm building my first major project, it's an Arduino Leonardo clone mixed with Arduino Pro and some other features. I've finally finished routing the board and it's quite cramped because of board size restrictions.

It passes Seeedstudio DRC with the exception of the pads on the sides of the board which are about a micrometer too close to the edge, I don't think it will be a problem during production.

My general questions are:

• My ground fill passes by some very narrow places sometimes (under the MCU), is that a problem? I don't plan passing a lot of current, but would it be good practice to add some wider sections or vias, even if it makes ground loops?
• There's a buzzer right above the MCU, I didn't find the resistive value in the datasheet, I know the MCU can safely source/sink 40mA maximum on a pin and I don't want to go above, how do I know it won't fry it, or do I have to put a resistor there myself?
• The quartz is on the right of the buzzer, its lines are very close to some IO pins (which are also UART TX/RX pins), I fear they might induce some undesirable currents in the quartz lines, but I don't know if it's true.
• I've got some right angle routing at some Y intersections, I don't know if I should route it differently or it doesn't matter.

Otherwise any advice or remarks are welcome.

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[free_electron]

what kind of buzzer are we talking ? iductiv ? pizeo ? self-oscillating ?

it all depends ...

[Solenoid]

what kind of buzzer are we talking ? iductiv ? pizeo ? self-oscillating ?

it all depends ...

I put the link to the datasheet in first post, the model I'm planning to use is PS1240P02BT, it's a piezoelectronic buzzer.

[marshallh]

1. Before reading any of this, know that your board will probably work just fine, save for an actual wiring error. Routing is noobish but sufficient. I have seen many boards far worse.

2. Your design suffers from poor grounding. Start picking critical ground nodes and follow the current return path to another ground node. You might realize the problem here, that is you have lots of useless copper dangling around doing nothing useful except picking up noise. Solution is to put on stitching vias (probably 10-20 would be enough) to lower the inductances of your ground return paths. Try a 3x3 grid of vias under the MCU. Attached image with where I would put stitching vias.

3. USB data lines - they are differential, route them tightly together. That means moving the series resistors very close.

4. Yes you do want series current limiting resistors for your MCU pin driving the buzzer.

5. With xtals and clock lines generally the closer the better, while keeping them isolated from other signals, your layout here isn't a problem.

6. There is a lot of wasted space on the board , which is not a problem at all, but if you wanted to condense it down further you could probably cut the area in half.

[Solenoid]

1. Before reading any of this, know that your board will probably work just fine, save for an actual wiring error. Routing is noobish but sufficient. I have seen many boards far worse.

2. Your design suffers from poor grounding. Start picking critical ground nodes and follow the current return path to another ground node. You might realize the problem here, that is you have lots of useless copper dangling around doing nothing useful except picking up noise. Solution is to put on stitching vias (probably 10-20 would be enough) to lower the inductances of your ground return paths. Try a 3x3 grid of vias under the MCU. Attached image with where I would put stitching vias.

3. USB data lines - they are differential, route them tightly together. That means moving the series resistors very close.

4. Yes you do want series current limiting resistors for your MCU pin driving the buzzer.

5. With xtals and clock lines generally the closer the better, while keeping them isolated from other signals, your layout here isn't a problem.

6. There is a lot of wasted space on the board , which is not a problem at all, but if you wanted to condense it down further you could probably cut the area in half.

I will add more vias, I don't quite understand the board general inductance well so I can't grasp the problem yet.

The wasted space is also for ease of soldering for people doing it for the first time (introduction to robotics in general), it has worked out quite well until now on an old version of the board with the smallest elements being in 0805 packages. If I could put elements closer or use smaller packages I would. The other thing was to remain true to the Arduino pinout.

[Solenoid]

Follow-up on my project: it's finished, tested and in production, I decided to go with a shield as I wanted more input/output components.

The main board: PRismino, the shield and a power board to power everything from batteries. The libraries are also included.

Thanks for your input.