Smallest time clock chip? - SOLVED

Hello, I'm like anyone elser trying to make there own thinest watch ever. So I'm curious what is the smallest timeclock I can get my hands on? I know there are shortages out there. But I'm still looking into making something even If i have to take it from something else for prototyping.

Joseph

If your plan is to use a processor along with the clock chip, then…

…ditch the clock chip altogether and just do the clock in software.

So now the question is what’s the smallest microprocessor chip you can get away with.

a7

I'm plan on using the esp32 processor I have 3 of them it is the s2 version.

Joseph

A chip like the DS3231 is actually quite small, vs. the PCB it's on. If you did a custom PCB, like a flex, you could shrink the thing down to a pretty small size.

I have a DS3231 it is a lot bigger then the esp32 processor.

Joseph

Sure it is, but consider the need for a crystal somewhere. If you get your timing from the CPU, you have to have some way to survive a power down situation. I don't know about the ESP32, but some STM processors I'm working with have a battery backed up subsystem capability, so the clock continues to run when the device is turned off. That is the main difference as far as software timekeeping goes. I haven't seen any provision on any ESP32 that I have for battery backup of the clock time (and sometimes some configuration settings in NVRAM), not yet anyway. You can get network time if you have wifi access or GPS, well great but you have to have some arrangement for that - antennas or logins. But maybe there is something I just don't know about it.

So just write the code on the esp processor. I am confident there is sufficient resources for a clock program and whatever else you wanna do.

a7

It’s a watch. Presumably it runs on a battery, so no worrying about battery backup, just like any watch.

a7

The issue is accuracy. A watch is not likely to stay in one place very much. So the internet connection would be switching and sometimes gone. So I think a good onboard clock of some sort would be better than just the MCU crystal. Maybe the ESP could support a good 32kHz crystal for that somehow?

Hello all Thank you very much for the information. I would love to use a ds3231 Module. Honestly I don't think I would have room for it. If I can find a smaller foot print for one other then a 1303 or a 1307 rtc I would be great.

Using a internal RTC might do the trick. But I think having a external would be better. I would have to see. This will take me some thinking on my part to see.

Joseph

Yeah why? I do not see any advantage, only disadvantages. Please share your reasoning.

TBC I am not talking about any kind of internal RTC "peripheral". I haven't used the processor you named, nor any chip with one. I'm just talking about writing some code that does what happens in an RTC chip.

Do you intend to use external time source over wifi or whatever?

a7

I will not be using wifi maybe bluetooth to the phone once in a while but at least 95% of the time it will be standalone not connected to anything.

To be honest I don't have a good reason to use a external rtc module other then keeping track when the processor is on or when it is in sleep need someway of keeping time.

Joseph

The smallest clock chip would be the silicon die itself. You would have to attach the leads between the die and the rest of your circuit. I doubt you own the technology to do this.
Paul

True Paul, Not me man. But I'm torn between using the internal rtc of the esp32 and a External of the Ds3231 which I do not know If I have room for one. I did mange to find a Ds3231MZ one smaller one but No one to be found other then aliexpress. That will take forever.

Joseph

Get an accurate TCXO (just like this TCXO), use it as the base clock for your MCU, and all the timers become just as accurate.

There's also the 32kHz version and you can use it as RTC clock source for newer MCUs (even the new TinyAVRs now have RTC peripheral built in)

THX, that makes sense.

Did I miss or have you said

  • the display you want to use
  • the dimensions of the volume available
  • the battery, and the operating time per charge
  • your hope for accuaracy in between fixes

a7

But will that be the time base when the processor is sleeping? This is a battery powered application.

The unspoken expectation of a watch is that it will be accurate to at least a few seconds a day.

What does a TCXO do?

'
Joseph

Google broken over there?

temperature compensated crystal oscillator

google any of those words you don’t understand.

a7

No, I thought it was part of something else for the Real time clock. Searched show up the crystal oscillator. But i was wondering if it was something else.

Joseph