Can the Capactive Sensor feature on nrf52 be used to wakeup the processor from sleep mode?

[Siddarth]

We need to put the processor in sleep mode (to conserve battery power) and wake-up the processor when the user touches the Cap Sensor pad.

Can you Cap Sensor in nrf52 be used for this feature? Will it be power efficient?

-siddarth

[ovrebekk]

Hi Siddarth

There is no dedicated capsense hardware in the nRF52, so you have to poll the sensor manually at certain intervals.

In between intervals you can use an RTC timer to sleep, which means the sleep current is around 2uA.

The sampling of the sensor requires more current, as you need to run a high precision timer to measure the charge time of the capacitive sensor. In other words the total average will depend on how often you sample the sensor. Sampling often will increase average current, but reduce the button latency, so you have to decide how long button delay/latency you can accept, and scale the sampling interval accordingly.

Best regards
Torbjørn

[ovrebekk]

Hi

Sorry for the late response.
I tried to find the developer responsible for the library, with little luck, but looking at the code it seems to follow a similar principle as the earlier github examples.

In other words my original answer still stands. You have to poll the sensor based on an RTC interrupt, which means that you can not use the system OFF sleep mode, but have to use the system ON mode instead.

Best regards