Using Atmega328p in a custom PCB

Hey guys,

im building a PCB using EasyEDA and was wondering if i could just get some verification that ive built this circuit correctly for proper operation of the Atmega328p and the ADS1115.

This circuit takes a differential reading from the ADS and displays it on an OLED.

I also added pins to upload to the 328 using TTL.

Ive never designed a circuit around the Atmega328 itself and ive created this using youtube videos.


Do not connect aref to vcc...

will this prevent it from working?

Having Aref connected to Vcc can cause badness if you set the ADC to use (internally) a Vref source other than Vcc.
Think of it as a multi-position switch. If the Aref pin is connected to Vcc and the internal Aref is set to Vcc, then Vcc is connected to Vcc - no problem. If the internal Aref is set to the internal 1.1V bandgap reference, then you've connected a 1.1V source to a 5V source, which is bad. How bad, I can't say. Whether it affects the chip if you DON'T switch the internal Vref, I can't say.

See section 24.5.2:

  • If the user has a fixed voltage source connected to the AREF pin, the user may not use the other reference voltage options in the application, as they will be shorted to the external voltage. If no external voltage is applied to the AREF pin, the user may switch between AVCC and 1.1V as reference selection.