What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

seajayshore — Thu, 16 Jun 2016 13:26:02 GMT

OK great. I'll take a look at doing this when I get a better moment. Thanks for the help so far!

I'm at least satisfied that I can beat the ~40ms downtime easily with simple hardware, having learned more about the nRF51's clocks etc. now.

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

Øyvind Karlsen — Thu, 16 Jun 2016 13:17:48 GMT

Supplying it that high is out of spec and will reduce device lifetime, it is likely that it will still function, but if you start to experience odd errors it can be worth trying to change chips. If you do not want to share code in a public forum we also have a closed support portal called MyPage.

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

seajayshore — Thu, 16 Jun 2016 13:13:05 GMT

To the 2nd part of your comment. I agree it's probably code related, thanks for your second opinion. I have infact done something similar to what you suggest by adding a simple RC-discharge combination to the enable pin (so that a capacitor keeps enable voltage high enough during this brief GPIO off period). That's all working quite nicely now. :-)

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

seajayshore — Thu, 16 Jun 2016 13:10:53 GMT

The voltage drop at the end of scope is due to the battery supply being ~4V that connects briefly to the enable pin, via the button which is also connected to a GPIO of the nRF51. I stupidly forgot to put some protection on this GPIO when I took this photo... Oddly the blue line, that responds with a higher-than-expected voltage exactly in sync with this higher supply voltage, is not connected to the enable pin. It's the response GPIO I'm using to test start-up times... Is there a chance that applying this too-high voltage to the other GPIO pin has affected how the other GPIO pins work? Or the nRF51 as a whole? The ~4V is obviously greater than recommended VDD+0.3V max. rating (so I'm correcting this in any case).

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

Øyvind Karlsen — Thu, 16 Jun 2016 13:01:13 GMT

Hi,

It's hard to say without seeing your code, I am also concerned about the voltage drop that occurs towards end of the scope reading.

This is very likely code related, however a simple hardware fix is to add a capacitor at the output so that you are not so vulnerable to GPIO bouncing.

Øyvind

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

seajayshore — Thu, 16 Jun 2016 12:52:25 GMT

Hi Øyvind,

Thanks v. much for your response. I worked further on this yesterday after posting and, from reading other related questions and playing with an oscilloscope I have confirmed exactly what you said.

Switching to the internal RC clock helped but seems to reduce start-up to ~100ms, not ~400us... But this could be due to some timeout code I'm not noticing however so I wouldn't worry about this.

As you suggested I now toggle the GPIO before any clock setup code and a solid <1ms response seems normal! Success!

However I now have a different issue. At ~100ms after initial response the GPIO pin drops to 0V for ~40ms (killing the LDO if I don't keep the button held).

What could be causing this?? Anything hardware-based? Or do you think odd mbed initialisation stuff...?

Here's a link to my scope reading: http://imgur.com/lnCCGYu Blue line is response GPIO, yellow is power.

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

Øyvind Karlsen — Thu, 16 Jun 2016 11:50:31 GMT

Hi,

The startup you're seeing is the low frequency clock which has a typical startup time of 0.3s. Please see the below logic analyzer trace where channel 0 is the toggled GPIO and channel 1 is the power. First with initialization of the LF-clock. (300 ms measured)

Then without initialization of the LF-clock. (0.8 ms measured)

For your application you can toggle the GPIO before starting the LF-clock. Or if you have a particularly need for clocking right at the start you can use the RC clock, which has a startup time of ~400 µs, before initializing your LF crystal later.

Best regards,

Øyvind

RE: What is the startup time of a discrete nRF51822 module vs nRF51-DK board?

seajayshore — Wed, 15 Jun 2016 14:48:05 GMT

BTW: I'm currently using mbed code to develop this. If there is some big overhead in mbed code execution causing this then perhaps someone could explain?