Are these schematics good?

Schematic for ATmega 32u4 and USB bus

The caps in the lower left go around any of the vcc pins on the 32u4
The labels on the pins are for a key matrix

schematic for the ATmega 4809

The resistors are for a light matrix

Schematic for Rotary encoders

The 32u4 and 4809 are connected via Serial communication.

The schematics look just fine and well drawn. You have a minor problem with the edges. When that happens to me I select all and just move it.

You ought to break out “updi” on the 4809, or you won’t be able to program it very easily.
Similar issue on the 32u4…

Really? I was thinking I could program the chips with an FTDI programmer, and I am not sure that the 32u4 has a UPDI pin

You need a way to install the bootloader, if you expect to load programs via the serial port. For that, it's very handy to have exposed the necessary pins for device programming. On the 4809, that's UPDI. On the 32u4, it's RESET, MOSI, MISO, and SCLK. If there are already external connections, you can theoretically connect to those with jumpers, but it's more convenient to have a standardized programming connector (which will also usually include power and ground.)

would FTDI be good? I would be able to burn the Bootloader and upload code.

AREF needs decoupling.

why would AREF need decoupling if I am not using it?

Have you prototyped your project to work out any code and/or hardware bugs?

Can you post a schematic with everything connected instead of a "search a word" diagram,

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

Have you prototyped your project to work out any code and/or hardware bugs?

Not really. I am still planning everything out and making adjustments to the schematic and basic PCB routing

Because it says you need to do it in the data sheet, because of the other things that rail supplies.

The schematics are OK but a lot depends on the software matching up to your hardware.

Trust the datasheet... Perhaps the analog comparator goes nuts if you don't do this, or current consumption by the analog circuitry jumps as it all starts oscillating or something. Never skimp on decoupling if you want an easy life. It might just be that the engineers designing the chip never analysed what happens without stable AREF, so they play safe.

Maybe I misunderstood that question, but you cannot burn a bootloader with an FTDI.

Worth getting one/couple of these;

Tom... :smiley: :+1: :coffee: :australia:

Where the datasheet says the AREF pin MUST be decoupled? According to the text the internal reference MAY be decoupled via the AREF pin. It is not required because you may use internal reference (i.e. for BOD) without connecting it to the AREF pin.

Whoops, yes I got it wrong - the problem of relying on memory rather than checking the datasheet - sorry for this. I'd still recommend decoupling it you never know if you might decide to use the ADC (internal temperature sensor for instance which uses the ADC). In the future you might want analogRead and its a shame if the PCB lacks pads for a cap on AREF...

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