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Just a quick check of microcontroller schematic before getting the PCB printed

j4cobgarby

Sep 18, 2018
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Here's a schematic for a keyboard I'm designed (the actual keyboard keys aren't included in this screenshot, of course).
Screenshot from 2019-04-15 18-34-10.png
Does this schematic look reasonable? I've read that I can program the Atmega32u4 over the USB connection using the pre-programmed DFU bootloader, but just in case that doesn't work I've got 6 pins coming off the chip which I can use for the 6-pin ISP interface.

I'd be very grateful if someone who's familiar with this microcontroller can look the schematic over quickly and give me any advice.

Thanks!
 

Harald Kapp

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Nov 17, 2011
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Looks like the GND connection to the USB port is missing (or maybe the label GND is taken as a connection, but I prefer placing a dedicated GND symbol):
upload_2019-4-23_11-26-52.png

Also: Vbus should only be connected to Vcc if the keyboard is powered from the USB interface.

It is also good practice to add decoupling capacitor right next to the controller's Vcc pins (2, 14, 24). Use 100 nF ceramic type and make the connections to the µC as short as possible:
one C between 1/2
one C between 14/15
one C from 24 to GND make the trace as short as possible, a GND plane would be best.
 
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