Newbie would like his DIY Arduino schematic checked

Hi All

I’m new to Arduino, I decided I would have a go at designing my own DIY Arduino using Eagle. I’m also new to Eagle.

At the moment, the board is meant as a generic base design. that is why none of the digital or analogue pins are connected. I am trying to get the board itself designed correctly before I move on and make boards with a specific function in mind.

The board will be done using the ATMEGA328P-AU and SMD components to make it as small as I can.

I have done what I feel is a good amount of research and feel that I have most things correct so far, but would like some brains that are more experienced to look over it. I would like particular attention paid to the iscp and serial header please, as I am not confident with them. I also have to 1 question that I have not been able to clarify.

Question 1, the crystal I have picked is EPSON Q22FA1280034112. This crystal is different to what I have ever used with my through hole experience. The confusion I’m having is that the crystal itself has 2 ground connections. I am assuming that the ground connections are for the case of the crystal itself. I am also assuming that I still need to have the actual crystal connections running to ground via the capacitors. In the schematic I have attached to this post, you will see what I believe is correct. I was hoping I could get confirmation that this is correct on this post.

I have attached an image of my schematic to this post for you checking please

thank you in advance for you time and experience

The only thing that stands out to me is how that crystal is connected. Are you sure that is correct?

I believe the crystal is connected correctly. Im just unfamiliar with ground connections on the crystal. Im currently trying to find some examples of how they are used like that. Thanks for taking a look

Looks pretty okay. Only couple of things:

X2 looks like a (weirdly shaped ;p) serial/bootloader program header, correct? In that case, it should NOT contain the reset but the DTR of the serial which is connected to the Arduino via a capacitor.

AREF should not connect to Vcc but to a cap to GND.

And yeah, crystal looks okay but I don’t know many with >2 connections. But the diagram suggests it’s connected to the casing which seems fine.

But in general I find it a lot easier to use an Arduino Pro Mini…

I think you have got the crystal connected wrongly.

Here is the pin-out from the datasheet:
Crystal Pinout.png

Pins 1 and 3 are the 'active ’ pins of the crystal, and should be connected to the pins of the microcontroller and the capacitors, as you have done.

However pins 2 and 4 are both connected to the metal case of the crystal. They should be connected to the circuit GND.

By connecting pins 2 and 4 the way you have, you have used the case to short circuit the two active crystal pins together.

This is how you need to connect the crystal:

Thanks so much for the pickup on the crystal, you guys have clarified it for me, I will make the corrections to the schematic in the morning. I will also correct the aref pin and run it to ground using a cap. The headers I have in the schematic are some surface mount molex 2x3 wire to board connectors. Hence why the look a bit strange. but I figure they should do the trick if I am using some jumper leads.

X1 and X2 look like the same connector. Make them different. Otherwise you are going to plug the wrong cable into one of them at some stage. At least make one male and one female.