Peripheral connection event gives unusual measurement peaks?

[Mathias]

Hi all!

I'm doing some tests on throughput and power consumption on the nRF51822, using SoftDevice 130. I use an application that sends 20 bytes notifications from slave to master on a connection interval of 7.5 ms. I already measured the throughput and get fine results (127, something kbps) when there is practically no interference. Now I'm trying to measure the power consumption on the slave, during the sending of those notifications. After some fiddling and reading, I could make a screenshot like this one:

What worries me is:

• The peaks are quite high?
• I don't really get perfect resemblance to the theory in the SoftDevice 130 specs (infocenter.nordicsemi.com/index.jsp. Especially (A), (B) and (C) are pretty weird (or maybe aren't there at all)?
• The event seems to take pretty long?

Is this still pretty normal behavior? Or is there a serious fault looming?

Thanks!

Mathias

[Sigurd]

Hi,

The behavior looks normal to me. The radio on the nRF51 will consume ~10.5mA when in TX mode with 0dB transmit power, and with DC/DC disabled. See the table 36 in Chapter 8.5.2 page 50 in the PS. Then you have the CPU consuming ~ 4.4 mA when it’s not in sleep mode. In total this will give you a peak current around 15 mA. Note that if you enable DC/DC mode, the peak current should drop with ~2.5 mA. (radio will consume 8 mA instead of 10.5 mA). Note that with such a short connection interval as 7.5 ms, the radio will be on more often and the average current consumption will naturally increase.

If you are interested in current consumption on the nRF51, I recommend taking a look at this post.

[Mathias]

Hi Sigurd!

Thanks for the clarification! :) We are testing some different connection intervals actually. But how is it that the RX and TX events each take 3 pulses instead of 1? And is it normal to have 100 - 120 µA current during the time between two intervals?

[Sigurd]

Q: But how is it that the RX and TX events each take 3 pulses instead of 1.

A: You typically get 1 of these pulse for each packet sent during the event. With 3 pulses you are sending 3 packets.

Q:And is it normal to have 100 - 120 µA current during the time between two intervals?

A: 100 µA could be a little high, but that depends on what other peripherals that are active. Are you using the UART or TIMER ?

[Mathias]

Okay, I used to get 6 packets but now I did another throughput measure and I see I'm only getting 3 now per interval. Maybe I messed something up with my code or with the firmware of the dongle, I'll see.

Not that I'm really aware of. I only use a timer to make the led blink during advertising but that's normally part of the template already I think. UART I don't use (didn't write anything for it).

[Mathias]

I think the unusual power consumption between intervals could be because I need to press and hold the button to make my application change the value of my custom characteristic. I'll try to change it to press and release to start changing.