hey there katjap, just now noticed this now (since it made the blog). after following matseng'e suggestion for traces, the supply lines look better.
Did i put too many vias in?
Never! :) They don't really hurt anything, although if the diameter is wide enough they'll tend to suck solder away from under the IC and cause voids (which can be a problem). You'll find that the further away from the IC you are, the less of a difference they make. DP had posted a good app note on the blog a while ago about via's under pads - they can be problematic for mass produced PCBA's.
Some comments (meant to be helpful):
- vias on the right side appear to be extremely close together (double check your ERC output to make sure they're not violating a minimum spacing constraint).
- on v 0.2 it looks like thermal reliefs have crept in on the top layer under the IC.
- double check the pull-back on your ground fill (I usually go with at least .01"/0.254mm isolation)
- ceramic power supply bypass caps should be as close to possible to the pins
- double check that your reference designators aren't under the components (you'll thank yourself for spending the extra time when you go to assemble/debug ;-))
- you may need a skillet/hotplate or toaster oven to assemble this
will the cap's go up in smoke?
A good rule of thumb is to double the supply voltage and you'll usually be fine (the 50V caps you have called out should be more than adequate).
katjap wrote:Is supplying my motor voltage right off a PSU really a good idea?
The ATX supply can handle the current without a problem. With constant current drivers and steppers you'll generally find that you can get more speed with higher voltages. This is because the higher voltage helps to overcome the inductance of the motor coil when switching.
Do i need to work on trying to seperate the ground plane for the motor voltage and the logic level voltages?
On ATX supplies, GND is GND so they're no real isolation, plus your IC is generating the logic voltage, so it will also be referencing the same GND. Further, you'll need to be referencing his ground on your connector for your drive signals. So, truly separate motor and logic grounds here isn't a possibility. Generally, if you think about how your low-speed currents flow (path of least resistance (i.e. straight line)) and position components accordingly, you'll be fine with one ground plane.
You had mentioned you were staying away from 0.1" headers (0.1" pitch connectors would be OK for your currents, but not to 3A). Depending on how you have things setup, you may or may not like to be able to easily unplug the motor from the board, without having to remember pinouts/colors. If you're using this for a CNC setup, you might want to add a pass through connector with an RC filter for your home switch on this board, then run that signal through X3 - I tend to put home switches close to the steppers, having them go to the same board can be helpful. It depends on whether you want this to be more of a general purpose breakout vs something specific to your project.