check simple PCB Arduino Uno and PCB for RA02

Ok, so you step-up the battery voltage from 3V3 to 5V using the ME2188 
and use this directly as VCC for the ATmega328P? I never designed such a 
step-up regulator, but I understand that the layout is quite critical, 
so watch out for the recommendations. C3 I don't understand (but doesn't 
hurt). C66 should probably be much bigger, like 4.7-100uF, or else there 
is such a big capacitor missing from 3.3VA to GND. R13 is rather small, 
will result in a very bright LED light shining, and might interfere with 
the ISP programming; I'd rather use 1k. The ATmega328P needs two 100nF 
close to the two power supplies, plus you forgot to connect pin 22 to 
GND. I usually use 10k as pullup R1 for RESET, but 1k might work as 
well. C4/C5 I usually use 18pF due to 2-4pF being contributed by the PCB 
itself. I also prefer C33 to be 10nF instead of 100nF as this will allow 
to switch the AREF source faster, but up to you. Usually there is also a 
10mH coil between VCC and AVCC to reduce digital (and in your case 
regulator) ripple impact on the analog measurements. Hope it helps.

Oh, one more thing out of curiosity: Why don't you use an Atmega328PB?

KR, Sebastian

Sebastian W. schrieb:
> R13 is rather small

oh yes! 1k looks fine

if you want to use ISP pins as GPIO use 470 Ohm in line to external use 
so a ISP can toggle ist!

358p ISP --- 470 Ohm --- LED or Input or other
      |----- to ISP connector

328p reset
https://www.kanda.com/files/isp_circuits.pdf
https://onlinedocs.microchip.com/pr/GUID-F626284A-58F0-4C25-A6F3-0EA5054F3E2B-en-US-6/index.html?GUID-B80B25FF-E9D7-4766-B562-DA197B8B938C
Note that Microchip/Atmel recommend a diode
in the reset circuit.

a diode at R1 and a capacitor to GND

a possible induktor to AVCC
https://www.mikrocontroller.net/attachment/373911/AVCC_Beschaltung.png

Mia schrieb:
> Is it Ok now ?

I made a typo, L33 should be 10uH, not 10mH. Also, the new C112 should 
go from AVCC to GND, i.e. VCC - L33 - AVCC - C112 - GND. See also the 
figure 24.9 in the Atmega328P datasheet (extract attached).

(For all the nitty-gritty details refer to 
https://ww1.microchip.com/downloads/en/AppNotes/00002519A.pdf. But in my 
opinion some of the recommendations in there are overkill.)

Watch out that the Pin 22 is still not connected to GND in your 
schematics. It seems your Atmega328P model is lacking Pin 22.

One more item. Your ME2188 will make it that the system will continue to 
run while draining the battery down to 0.95V (depending a bit on the 
power consumption). This will probably harm the battery when it is a 
rechargeable one. Maybe you should foresee a jumper which would connect 
the +3.3V source to one of the analog ports of the Atmega328P so that 
the software could at least detect that the battery goes flat and, I 
don't know, warn the user or so ...

KR, Sebastian