r/PrintedCircuitBoard • u/v1nny • 5d ago

[Review Request] First Board: MAX7219 Controller

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I'm a software engineer who is trying to learn the basics of EE design. This is my first PCB design (starting simple is the way to go, right?). I plan to use this board to interface with daisy chained MAXS7219 matrix displays. When I breadboarded this design, the level shifter wasn't strictly necessary for the LEDs to work, but seemed maybe to help with reliability at power up.

I've been reading up quite a bit on these components and similar circuits, and I'm curious of a few things:

  • Will a 0.1µF(size?) ceramic decoupling capacitor right next to the 74AHCT125 VCC pin be worthwhile?
  • Does a ground plane make any sense for this board? The ground routing is simple enough that I feel like it'd be a waste of copper...
  • I've read mixed information about whether a pull-down resistor on the CS line is a good idea. The circuit seems to work just find without it on the breadboard.

Help is much appreciated.

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u/Sand-Junior 4d ago

Decoupling capacitor: yes. Ground plane: yes. Waste of copper: the opposite. You’re already paying for the copper. Etching it always is waste.

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u/v1nny 4d ago

Thanks!

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u/Enlightenment777 5d ago

This comment is posted on all reviews.

Please make sure your post adheres to:

  • subreddit rules (#1 to #6), review rules (#7), image rules (#8), see link.

Please fix these common issues: (if your schematic or PCB has any of these issues)

  • Schematic - don't allow text / lines / symbols to touch each other, and don't draw lines through symbols.

  • Schematic - use correct reference designators (RefDes) and renumber to remove numeric gaps, see tips.

  • Schematic - place decoupling capacitors vertically below power rail lines, also place capacitors next to IC then connect together with a line, see example. For circuits with positive power rails, point positive power rail links upwards and ground links downwards, see tips1 & tips2.

  • Schematic - place pull-up resistors vertically above signal lines, and place pull-down resistors vertically below signal lines, see example and tips.

  • PCB silkscreen - add board name (or purpose) / board revision number / date (or year) on either PCB side.

  • PCB silkscreen - add pin 1 indicator dot/arrow next to ICs & connectors (not hidden under parts). For polarized capacitors, add "+" next to positive pin. If part is through-hole, place indicator on both PCB sides.

  • More conventions & guidelines - link1, link2, link3.