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This is the first time I've made a "more complex" PCB. Before I buy all the parts it would be nice if someone could check my design.

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ATmega32U4: Datasheet

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    \$\begingroup\$ Do you really need the 16 off 1N4007 diodes which are 1000V 1A rectifiers when a general purpose Si diode such as the 1N914 ans it's brethren are considerably cheaper? \$\endgroup\$ May 22, 2023 at 12:06
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    \$\begingroup\$ The question lacks details what the device is supposed to do so it is unknown if the provided schematics need modifications or not. \$\endgroup\$
    – Justme
    May 22, 2023 at 15:09
  • \$\begingroup\$ Why are rows and columns mixed to different ports? Why pull-downs are missing? Why diodes push high as you can enable internal pull-ups if diodes pull down? What frequency crystal that is? Are you sure you checked the data sheet if the supply diagram is OK? Why USB resistors are 220 ohms? \$\endgroup\$
    – Justme
    May 22, 2023 at 15:13
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    \$\begingroup\$ Regarding USB, review chapter 21.5 Design Guidelines of the datasheet. If the manufacturer 'highly recommends' something, I would do it. Especially if it's my first design using that certain chip. \$\endgroup\$
    – Velvet
    May 22, 2023 at 15:21

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Explain the function of the circuit first.

  1. The circuit seems to be supplied from USB port "directly". Although the spec suggests the bus voltage to be within 4.75~5.25V range can you still trust the bus to be "clean" to feed directly to the chip?
  2. No decoupling caps are present for each VCC pin of the chip.
  3. Doesn't 220R seem a bit high for USB comm line series resistance? The characteristic impedance is 90 Ohm differential, so 220R may cause some communication problems. I'd replace them with 22R resistors (NOTE: If you mean 22R with those 220s (R2 & R3) then R4 shouldn't be 33R as the LED current may exceed the pin's current rating and damage the chip, depending on the LED e.g. for a red LED the current will be 88mA which is way above the rating).
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  • \$\begingroup\$ yes, it is normal to trust USB voltage although you still need decoupling capacitors. \$\endgroup\$ May 22, 2023 at 15:59

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