Capacitive Touch for Lock

[Deepak Gupta]

We are considering using the nRF52832 / nRf52840 for a smart lock application with a capacitive touch keypad. Currently the product is using a Cypress Cap sense product for the capacitive keypad function. The requirement is to do away with the Cypress part and use the Capacitive touch function on the nRF52 parts. It is a lock, so the keypad is the most critical part and reliable operation of the capacitive touch will be key. 

Checking to see if anyone else has experience working with the capacitive touch function of the nRF52 parts and results thereby. I do not see much in terms of documentations / examples for this, so any real world test / experience will be of great help. 

Thanks.

[Einar Thorsrud]

Hi,

The SDK has the Capacitive Sensor low-level library and Capacitive Sensor library, which are demonstrated by the Capacitive Sensor Low-level Example and Capacitive Sensor Library Example. There is also the older Capacitive Touch on the nRF52 series tutorial.

As you can see there are two possible methods with the nRF52832: relaxation oscillator and RC charge timing. The former is only possible on the nRF52832, but it is not suitable for production due to erratum 84. The latter can be used with both nRF52832 and nRF52840, but you should note that the implementation is quite simple, so particularly the calibration algorithm probably needs quite a bit of work in order to work stably in a changing environment (tings like temperature, air humidity etc have effect on the capacitive sensing).