I have a circuit as shown here:




The board was assembled via JLCPCB with the following parts:

C37+C38 = https://jlcpcb.com/partdetail/2000-CL10C200JB8NNNC/C1648 (info + datasheet link)
Y2 = https://jlcpcb.com/partdetail/SeikoEpson-Q13FC1350000400/C32346 (info + datasheet link)
U17 = https://jlcpcb.com/partdetail/NxpSemicon-PCF8563TS_5118/C27397 (info + datasheet link)
C36 = https://jlcpcb.com/partdetail/53938-CL05A105KA5NQNC/C52923 (info + datasheet link)


The problem is: when I set the RTC time and date it stays there forever. It's not incrementing.
I have multiple boards assembled by JLCPCB and tried 3 of them. They all 3 have the same issue.
So it must be a design error I'm afraid.

Any thoughts?

 

I have to admit I have never worked with crystals myself as I have always used internal clocks or oscillators for my clock sources so I may be wrong.

The application diagram on page 36 of the RTC datasheet looks nothing like your circuit. Most times those diagrams are the bare minimum to success with any IC. Other than that I would say you have too much capacitance on your crystal from what I gather... too much will make it run slow and too little will make it run too fast.

 

Have you properly set register 1, bit 5 (stop)?

The time won't update in stop mode.

 

I'm using Adafruit's library and even the included example ( https://github.com/adafruit/RTClib/blob/master/examples/pcf8563/pcf8563.ino ) doesn't work here. I assume they are correctly setting the register bits as it's supposed to be a working library...



So... maybe I do need to desolder the two capacitors I added? The datasheet does indeed not list those like I added them.
(I actually copied this part from another schematic I found online. Maybe that one was incorrect to start with...)

 

Try it with C38 removed.

 

I removed C38 but nothing has changed. Time is still not increasing.

 

I tried removing C37 too, same issue.
I even tried several different libraries, they alle have the same issue: time is not increasing.

I'm scratching my head on this.. Can't figure out why it's not working

 

Someone suggested replacing C37 with a 10pF capacitor and removing C38.
I tried this, no luck either

 

You do have pull up resistors on your I2C bus lines of course (say, 4k7's)?
Just checking!

 

Yes, and there are other i2c devices on the same bus working perfectly tine too.

 

I tried replacing C37 with different values (10pF, 15pF, 20pF and 22pF) but I can't get it to work.
The clock output stays flat and measuring the frequency at OSCO I get:

10pF: +- 19kHz
15pF: +- 19.7kHZ
20pF: 17kHz
22pF: Flucutating between 16-17kHz

So I'm unable to get 32.678kHz on the OSCO pin.
Should I try with other different capacitors? I'm not sure what else to try...

 

hi akke,
Is this video link any help?
E

 

No... But I'm not sure what part of this video you wanted to show me?

 

I do now wonder if the crystal I'm using is the right one... The one I'm using is one of JLCPCB's basic parts: Seiko Epson Q13FC1350000400 32.768kHz 12.5pF ±20ppm SMD3215-2P Crystal.

This is an SMD Crystal Resonator but that's not a Quartz crystal, right?
So I'm just f*cking using the wrong crystal for this RTC. It might just not work with this SMD crystal resonator?

 

I do now wonder if the crystal I'm using is the right one... The one I'm using is one of JLCPCB's basic parts: Seiko Epson Q13FC1350000400 32.768kHz 12.5pF ±20ppm SMD3215-2P Crystal.

I had wondered that myself, but without any practical experience with crystals I wasn't sure. I do know there are different ways of cutting the quartz that impact how it works, but was not able to find any details in either the RTC or crystal datasheets. I do notice a formula in the footnotes on page 34 of the RTC datasheet that may be of interest, but I'm not understanding how to apply it exactly. The crystal datasheet isn't making sense to me (probably a lack of experience issue)

At any rate I did dig through my parts box and found a few of the RTC that I had bought a few years back and never managed to get working so now I'm really curious. The part number sounded familiar...

 

Is there anyone in here with more knowledge who can help?

 

Have you tried a different crystal?

 

Not yet. I’ve ordered a different one for testing. Will test as soon as it arrives.

 

I tried again with these crystals:

SC32P-12.5PF20PPM ( https://www.mouser.be/ProductDetail/628-SC32P-125PF20PPM )
CM315D32768DZCT ( https://www.mouser.be/ProductDetail/695-CM315D-32.768CT )

Changing the crystals didn't change anything. The time is still not ticking with the RTC