Advice on my barebones PCB (ATMega328)

Hi all,

I’m trying to cobble together a PCB based around an ATMega328 smd which I intend to run at 3.3v / 8Mhz. I’ve followed the advice found here, but I wonder if you wouldn’t mind casting your eye over the fritzing plan before I press ahead?

Thanks in advance!
Mark.

ATMega328 Barebones.png

How about a schematic?

My humble opinion (I'm not a pro pcb designer but a hobbyst):

-Why are you using Atmega328 SMD when you are using thorugh hole crystal and through hole 100 uF cap. I'd use Atmega328P DIP or I'd move everything to SMD, otherwise there is no point on using SMD micro when wasting those space.

-Quick question: What is 3.3 V In? A screw terminal or male hearders?

I often use thru hole crystal vs SMD. The SMD pads take up a huge amount of space.

Lately I've gone to using this smaller SMD part for the crystal. http://www.digikey.com/product-detail/en/ECS-160-20-3X-TR/XC1776CT-ND/2676640 You can how much smaller it is here, 4x7mm,where it was purchased by accident and installed on 5x11mm pads

Still want to see a schematic tho. Otherwise, might as well ask for a review of this:

Thanks for help all - particularly for the tiny crystal. I’m setting myself the challenge of as small as possible - in what will eventually be nodes in tiny home-automation nodes.

Have attached a (cruddy) schematic here. Sorry for the quality - if it’s no good, I’ll try again in the morning.

If running off 3.3v, you don't need the 8mhz crystal at all, unless you need the clock to be particularly accurate. You can set the fuses to run at 8 mhz off the internal RC oscillator.

AREF should NOT be connected to Vcc. Just a cap to ground.

You might want to look at something more capable than Fritzing if you’re planning on having wires connect to the rest of the m328 pins.

DrAzzy: If running off 3.3v, you don't need the 8mhz crystal at all, unless you need the clock to be particularly accurate. You can set the fuses to run at 8 mhz off the internal RC oscillator.

Thanks for the advice all. I'm intending to hook up to a nrf24l01 - am I right in thinking I probably want an external crystal, or can I get away with the internal oscillator?

Ceramic resonators are another option if size is an issue. You can get through hole versions, but they're not much smaller than a regular crystal. SMD versions are tiny though.

Not quite as accurate as a crystal, but better than the internal oscillator, and used as standard on the Arduino Nano.

Ian.

markpeace: Thanks for the advice all. I'm intending to hook up to a nrf24l01 - am I right in thinking I probably want an external crystal, or can I get away with the internal oscillator?

You only need accurate timing with serial; the NRF24L01 uses SPI. The internal oscillator would be fine.