Arduino DUE RTC crystal

[ElectroNub]

Hi all,

I have a cheap Arduino DUE clone and I found that it does not have the 32khz crystal installed on the board. I would like to make use of the on-board RTC rather than use a separate module.

I read somewhere that you can find the required crystal on a discarded cell phone. I think I found one but I cannot tell for sure. I am hoping one of you can confirm my found treasure is what I think it is. Picture attached below.

The part is the right size for the pad on my DUE. It is labeled A234N in the picture.

Also, what should I consider when looking for capacitors? The DUE schematic shows 22pF. Is that value critical or can I whack in a couple caps that are the right size for the pads from the same donor board? That pair just north of the battery in the picture look like the right size.

It seems my meter can only read down to nF so testing them might be a problem.

Any help appreciated. I'm just a nub trying to figure this stuff out

[ElectroNub]

P.S. My meter has better resolution than I remembered. Checking 22nF caps is not a problem. Smallest I've found so far is 100nF.

I'm a bit confused. Smaller physical size caps seem to have have larger values. This SMD stuff makes my brain hurt lol!

[neslekkim]

My original Due don't have this crystal either, does it mean that the ones produced today have the crystal?

[technix]

I don't remember any Arduino ever had a RTC crystal at all. Maybe the designer of your clone decided to add footprints for it?

I won't use an RTC crystal there actually, instead I would prefer using Maxim DS3231 as it packs a 2ppm guaranteed precision DTCXO and all required I2C RTC logic, and available from some Shenzhen supplier for US$0.25/each or less for quantity of 10.

[neslekkim]

I don't remember any Arduino ever had a RTC crystal at all. Maybe the designer of your clone decided to add footprints for it?

When the DUE came, there was some pictures with the crystal, and some without, my due have the footprint, but not the crystal.

With the pads:
http://www.arduino.cc/en/uploads/Main/ArduinoDue_Front.jpg

with the crystal:
http://www.arduino.cc/en/uploads/Main/DueUSBPorts.jpg

[technix]

I don't remember any Arduino ever had a RTC crystal at all. Maybe the designer of your clone decided to add footprints for it?

When the DUE came, there was some pictures with the crystal, and some without, my due have the footprint, but not the crystal.

With the pads:
http://www.arduino.cc/en/uploads/Main/ArduinoDue_Front.jpg

with the crystal:
http://www.arduino.cc/en/uploads/Main/DueUSBPorts.jpg

Oh okay anyway my Due clone does not have that populated though.

[ElectroNub]

I don't remember any Arduino ever had a RTC crystal at all. Maybe the designer of your clone decided to add footprints for it?

I won't use an RTC crystal there actually, instead I would prefer using Maxim DS3231 as it packs a 2ppm guaranteed precision DTCXO and all required I2C RTC logic, and available from some Shenzhen supplier for US$0.25/each or less for quantity of 10.

Great suggestion! But that's not the fun way! I figured this is a good opportunity to learn about crystals (and I am). Plus my discarded cell phones are free and there is no shipping time. Accuracy can be software compensated and the temperature is reasonably stable for my project. I'm also looking for the satisfaction of "hacking" something just for the sake of hacking it I got a pair of free DUE so I have nothing to lose and knowledge/experience to gain!

Just need to figure out if this chip that I have already de-soldered is in fact a watch crystal...