ATmega Crystal and power layout

Thread Starter

ShayneColbert

Joined Mar 3, 2019
4
Hi,

I have finished designing my first circuit boards and am uncertain about a couple of things. First of all I know that I should connect both sets of ground pins and +voltage pins on the chip. My question is is the way I have connected them on my two boards ok or was it unnecassary to have two seperate cable runs for each one. Shall I just send one power cable to them and link them together.

My second question regards the layout for the crystals. Originally I had them laid out like in the first circuit (Backpack Board). But I am not sure if this is the correct way to do it. I then changed them to the layout in my second circuit(Utility Board). I beleive this is the way atmel suggest laying them out. It has a solid ground plane on the second layer. They are two layer boards. Should the ground plane below the crystals ground area be seperate from the rest of the ground plane or not. And should I link it with vias. I'm not sure if it should be made separate as I don't want to create a ground loop in the ground plane. The board is going to be used near an RF module so I want to make it as rock solid as possible.

Thanks in advance for any help.

Backpack board.png ATmega328 PCB.png
 

DickCappels

Joined Aug 21, 2008
5,943
Both of your crystal layouts should work fine.

You can just tie the power supply pins together. It is a good idea to make provisions for a choke or resistor to filter the analog powwe supply in case of noise problems.
 

Thread Starter

ShayneColbert

Joined Mar 3, 2019
4
Both of your crystal layouts should work fine.

You can just tie the power supply pins together. It is a good idea to make provisions for a choke or resistor to filter the analog powwe supply in case of noise problems.
Thanks for your advice. I'm not actually using any of the analogue capabilities of the chip and I'm powering from a battery so I'm guessing I wont need a choke or resister on the analogue power.
 
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Wolframore

Joined Jan 21, 2019
1,321
There’s 2 ATmega328 and an ATtiny84 on the first board. Why not just use an ATmega2560 or an STM32? How many IO’s do you need? Are the pins connected directly to motors?
 
Last edited:

Thread Starter

ShayneColbert

Joined Mar 3, 2019
4
There’s 2 ATmega328 and an ATtiny84 on the first board. Why not just use an ATmega2560 or an STM32? How many IO’s do you need? Are the pins connected directly to motors?
The two atmega328s are monitoring multiple Infrared inputs and they need all the cpu cycles they can get to make sure no data is missed. The ATtiny84 is controlling ws2812b leds and the drivers contain tight assembly code which will interfere with the code on the 328s if i run all the functions from the same chip. Basically I have multiple chips so as to give me more processing power. Plus I want through hole components.
 
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