Capacitance reading circuit for nRF51

RE: Capacitance reading circuit for nRF51

Jørn — Fri, 23 Jun 2017 09:28:53 GMT

The measurements are described in the driver documentation linked in my answer. The Timer library is used which is based on the RTC peripheral.

RE: Capacitance reading circuit for nRF51

Ehsan — Wed, 21 Jun 2017 14:33:30 GMT

What would be the best way to measure the charge time? Also, what peripherals would be required?

RE: Capacitance reading circuit for nRF51

Brandt — Wed, 24 May 2017 23:23:51 GMT

Thanks a lot for your advice, Jorn. I'll look into the information and give a try.

RE: Capacitance reading circuit for nRF51

Jørn — Wed, 24 May 2017 11:57:52 GMT

Hello Brandt

We do have a capacitive sensing driver, and a library. Information on the capacitive sensing driver can be found here, and information on the capacitive sensor library can be found here

With the nRF51 it charges the capacitance with an extra output pin, and measures the charge time. Then you can calculate the capacitance from that. With the nRF52 you can use the comparator as a relaxation oscillator (see the link in the driver section above), whose frequency will be dependent on the capacitance.

We also have a couple of examples for capacitive sensing, these examples can be found at [SDK folder]/examples/ and are called csense and csense_drv. You can find the example documentation here and here. Examples for the nRF51 series is not available in SDK13, but you can find them in SDK12.2

Best regards

Jørn Frøysa

RE: Capacitance reading circuit for nRF51

swoudlxy — Tue, 23 May 2017 20:21:36 GMT

Hi Jorn, the capacitive sensor is acting as a pressure sensor. The output capacitance will change according to the variation of the thickness of the dielectric sandwiched between two conductive plates. Therefore, we are wondering whether there is a proper circuit that can read the capacitance of the sensor.

RE: Capacitance reading circuit for nRF51

Jørn — Tue, 23 May 2017 14:28:56 GMT

Hello Brandt, you say not capacitance touching sensor, do you by that mean no capacitive sensing as used in place of buttons? What will the purpose of your sensor be? What will change the capacitance?