Always-On Battery Draw for Seeed XIAO BLE Sense nRF52840


I am making a board-game timer device using the Seeed XIAO BLE Sense nRF52840 and 19 LEDs. I can estimate the draw of the LEDs, but I have no idea how much the MCU will draw. It will be always on (no deep sleep) and it will be using the BLE to connect to a phone. It will be ready to receive data at any time, but it will actually receive or send data only every two minutes or so. Each data burst is small. It will also use the accelerometer to detect movement. I will be running CircuitPython on it.

What is the ballpark mA draw from such usage (not counting the LEDs)? Ballpark is fine. I just want to make sure I get the right size battery for a 4 hour game.


PS. I did search for this info, but I only ever found discussions about deep sleep!

Hi there,
Spec’s with BLE connection, I see average between and higher 40ma. ,Burst transmitions and it could go higher.
Better approach is to use the battery specs and the online battery calculator, (search links in post for PPK) you’ll find it all, a lot of onfo ,graphs and examples.
GL :smiley: PJ :v:

Oh great, thank you! Can you tell me where you found those numbers? Just so i know where to look for something like this in the future. You says spec, as in specifications? If the seed studio or maybe the chip?

And, 40 mA is less than I expected! Great! I can use a smaller battery.

Is this tool helpful?

Hi there,
This is from Oli over at Nordic Semi, Basically my device does use the gpio and it switches a darlington pair of FET’s to fire a solenoid so the Devices average Current was Higher in mi Graphs. YMMV but 40ma was the target I used to stay under as he recommended, Way under (sleep most of the time) is much more efficient.

50 mA should be enough. If you use LDO mode and use output power of 8dBm (max on nRF52840) the radio itself will draw almost 30 mA from VDD, If you add CPU run current and other miscellaneous things you will still be under 40 mA. The total peak current consumption of the nRF52840 should always be lower than this (assuming you don’t sink or source any significant current on the gpio pins). Note that this is the least efficient mode of the nRF52840 and not recommended for power efficient designs. If you enable the on-chip DCDC converter(s), the current consumption will be much lower for the same voltage on VDD.

You know that the nRF52840 has a “high voltage” DCDC converter with a maximum input voltage of 5.5V. This is in addition to the “low voltage” DCDC converter with a maximum voltage input of 3.6V, like the one on nRF52832. See the Product Specification for more information. In addition to powering the nRF52840 the high voltage regulator can supply external components with up to 25mA through VDD."

If your device is always plugged into usb, you can power the externals up to 25ma.@5V
GL :slight_smile: PJ