Does nrf51822 have a clock?

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 15:11:02 GMT

Unfotunately yes I'm sure.. It will happen. T.T @Wojtek

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 15:08:57 GMT

Thanks. There is no way to answer right because I didn't explain everything. but Thanks. @BLEdude

RE: Does nrf51822 have a clock?

Wojtek — Mon, 14 Sep 2015 15:07:38 GMT

Maybe a bit different approach - are You sure that it is needed to totally TURN OFF nrf51? It doesn't draw that much current when in system on... You can measure time using internal RTC then. Also You can monitor your battery by internal ADC.

RE: Does nrf51822 have a clock?

BLEdude — Mon, 14 Sep 2015 15:06:43 GMT

Ohh I see. I was unclear as to what time difference you were trying to measure. If trying to see how long the device is off, then yes, I can't really see any way besides having a dedicated clock.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 15:04:31 GMT

If device could not figure out how long it's turned off itself without phone, this can't be solved.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 15:01:00 GMT

Thanks. but it doesn't solve this problem because what if device turns off and he turn on again and again and few days later connect to phone? @BLEdude

RE: Does nrf51822 have a clock?

BLEdude — Mon, 14 Sep 2015 14:58:41 GMT

Hrmm... Depending on how precise you need to know the time difference, you could create a timer which will save the time every x number of seconds. That way if your device suddenly dies, you will at least have the time within x number of seconds. Hopefully this makes sense.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 14:54:06 GMT

@BLEdude What if device turns off or battery is gone? That's why I asked you guys. It has to have clock something. I thought it has it of course.

RE: Does nrf51822 have a clock?

BLEdude — Mon, 14 Sep 2015 14:52:33 GMT

Maybe instead of sending its last time to the phone, the device can save the time to its persistent storage. And then when it reconnects to the central, it can send the time it saved, and the central can figure out the difference in time?

RE: Does nrf51822 have a clock?

Michael Dietz — Mon, 14 Sep 2015 14:37:47 GMT

I think so. Sounds like you'll need to do what Wojtek said.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 14:32:51 GMT

So, the result is that I need to add some external stuff? Thanks.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 14:31:34 GMT

@Michael. Thanks for your help. but as you said little, there is no guarantee that device sends something to phone before it turns off. The phone could be at the outside or could be not connected with device. So I need to make device to figure out itself.

RE: Does nrf51822 have a clock?

Michael Dietz — Mon, 14 Sep 2015 14:27:32 GMT

Maybe you could do something hackish/clever:

1.) Device sends a flag right before it turns off - the phone now starts keeping track of time. 2.) Device starts keeping track of time once it turns on. After the device connects to the phone it sends the phone a flag with the time elapsed since it turned on. Now the phone knows (almost exactly) how long the device has been off. 3.) This time can then be passed back to the device if needed.

Downfall - any time the device is powered off the phone will need to be keeping track of time - this means that the app will have to run in the background or you will need to do some type of service on the app side.

But this might allow you to avoid another separate clock/power source. There could be other solutions as well

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 13:53:34 GMT

@Wojtek do you mean I can't do what I want with just nrf51822?

RE: Does nrf51822 have a clock?

Wojtek — Mon, 14 Sep 2015 13:51:01 GMT

Then You need external RTC with independent power source to keep the time counting when nrf51 is not powered.

RE: Does nrf51822 have a clock?

benevbright — Mon, 14 Sep 2015 13:43:29 GMT

Hi, Thanks. What I need is to know difference of time between before and now even if device is turned off. I don't want to know what the time is.

RE: Does nrf51822 have a clock?

Michael Dietz — Mon, 14 Sep 2015 13:35:23 GMT

The nRF51 has an internal 16 MHz RC oscillator.

However, if you want to use the RADIO peripheral (you want to use BLE or ANT etc...) then you MUST include an external high frequency clock (see nordic's reference designs).

Also an external low frequency 32.768 kHz crystal is optional (reduces current when using BLE and other timers) but the interal RC oscillator can generate this signal. See this post: devzone.nordicsemi.com/.../

But if you are talking about a real time clock - a clock that stores the time in hours and minutes (i.e. 12:48) then you will need to implement this yourself using the TIMER peripheral.

-Mike