Recommended board for low power BLE project?

[iacomus]

Hi!

I'm working on a project and looking for recommendations on an Adafruit / Arduino compatible board. The project is quite simple - control three LEDs over BLE / Bluetooth

Must have:
- BLE / Bluetooth
- Lower power consumption - runs off a LiPo battery for a week
- Drives three 3V LEDs at 20ma for 8 hours a day
- Connect over BLE / Bluetooth from Windows / Mac without a specific Bluetooth dongle (native Bluetooth on PC / Mac)

Nice to have:
- Recharge battery over USB
- Monitor battery level
- Over the air firmware updates
- Ability to switch in to low power mode / idle state

Initial thoughts are Adafruit Feather nRF52 Bluefruit LE - nRF52832 https://www.adafruit.com/product/3406

Any and all suggestions welcome - thanks!

[adafruit_support_mike]

- Drives three 3V LEDs at 20ma for 8 hours a day

This will require 480mAh per day, so you'll need at least a 3400mAh LiPo.

Most of our dev boards use 11mA, and it will be more energy efficient to use one with BLE built in, like an nRF52832 or an nRF52840. That way you don't have to supply power for an external BLE module in addition to the microcontroller. BLE radios use about 30mA, but only for a few milliseconds at a time. The energy cost of running them will depend on how often you want to send messages to the board.

168 hours of 11mA translates to another 1850mAh of battery power, so the simplest version of such a project would need about a 6600mAh Lipo.

You can reduce the idle power consumption if you're willing to let the microcontroller sleep periodically. The cost is that you won't be able to run the LEDs or use BLE during that time, so there's a tradeoff between saving power and waking up long enough to be responsive.

[iacomus]

Thanks Mike, that's super helpful! I'm going to need a chunky battery :)

Of the nRF52832 and nRF52840 dev boards, do you happen to know the quiescent and shutdown current draw of the boards? Does the Adafruit firmware for the boards support the low power management capabilities of these microcontrollers when in standby / shutdown? I had seen in one of your product videos that some of the nRF52832 and nRF52840 dev boards had a quiescent current draw of less than 1mA? It was mentioned in this video https://youtu.be/tKmqyF25WlI but I'm struggling to find it in the product details.

[adafruit_support_mike]

If the microcontroller is just idle, the boards will use about 11mA. When the microcontrollers are sleeping or the voltage regulator is disabled, parasitic leakage in the board comes to about 80uA.

If you're willing to live with a sleep-and-wake cycle, you can also use the TPL5110 low-power timer:

https://www.adafruit.com/product/3435

It controls power to the rest of a system, and draws less than 100nA while it's sleeping.

[PWK]

iacomus

I use the Adafruit nRF52832 and was able to get the current draw down to around 600 uA without using sleep mode. Any questions let me know.

Paul

[iacomus]

Hi Paul, that’s amazing, did you have to make any major circuit modifications or was it all in code?

Cheers,

James.

[PWK]

James

I did not make any circuit modifications. I spent a lot of time but all my effort was in the code. These two lines of code added to the void setup had the most effect in reducing power.
Serial.end(); // Shut this down to limit power
sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE); // This saves power approx. 500 micro amps (.5 milli amps)

There is a lot of discussion on this forum if you search low power nRF52832.

Paul

[iacomus]

Super thanks Paul that’s really useful. I’ll dig around the forums.

I went for an Adafruit Feather nRF52840 Express in the end. Hopefully it has similar options for making it low power.

James