Hello, I'm planning to try the NordicBlog; Capacitive Touch on the nRF52 series to test a button type or a up-down slider type.
I'm planning to use an nRF52832-QFAA for a new 2 layered FR-4 PCB.
My application will be based on the UART service example, so it will use S132 SoftDevice.
These are my questions;
- Before starting my questions, I wish to check the blog's notice;
The blog introduced 2 ways.
1. Resistor capacitor (RC) charge timing.
2. Relaxation oscillator (RO).
However,
Due to erratum 84 (COMP: ISOURCE not functional),
capacitive sensing using the relaxation oscillator method is not usable in a real product
with the nRF52832, as it will only work reliably in room temperature.
Then, if I choose the RC charge timing method,
Two pins are required per button:
- one GPIO output pin for charging the sensor capacitor via a large resistor (e.g. 1–10 MΩ).
- one analog input pin connected to the sensor electrode at the same point as the GPIO
(without the resistor). This is used to measure the voltage over the sensor capacitor.
I need 2 pins (GPIO output pin & Analog input pin) per button to use that method and this is feasible in other temperatures, right?
-
I hope that the capacitive touch button can be an input that can wake the nRF52 from the System OFF mode or the sub power (low power, by calling
sd_app_evt_wait) mode.The device can be put into System OFF mode using the POWER register interface. When in System OFF mode, the device can be woken up through one of the following signals:
- The DETECT signal, optionally generated by the GPIO peripheral
- The ANADETECT signal, optionally generated by the LPCOMP module (OMITTED OTHER OPTIONS)
Since the RC charge timing method uses an analog input pin, I wish to infer that this satisfies option 2 (ANADETECT signal) to wake the nRF52 from System OFF mode.
(PLEASE NOTE THAT I SAID INFER)
Then, by touching a button type capacitive touch or sliding the slide type touch sensor,
can this make the nRF52 to wake up from System OFF mode or low power mode?
- The blog didn't notice about power consumption while using capacitive touch sensors.
This is my concern while creating a product that uses a 1000mAh Li-Po battery;
-
should I add other vendor's capacitive touch solution that claims that it uses less than a µA?
-
Or should I lower the material cost even though the nRF52 consumes heavy currents (if it really does, maybe more than 2mA per button? So I really hope not) while using its capacitive touch solution?
Suppose I created 2 circle shape button type touch sensors that use the RC charge timing method, have the radius of 10mm, and connected 10MΩ resistor at the GPIO output.
Let's say that these are created on a 1.6mm thick 2 layered FR-4 PCB that has nRF52832-QFAA.
If I know the size of the touch sensor and the resistor value, can I estimate the current consumption caused by the touch sensors?
Too bad that the new Nordic Thingy52 doesn't have a capacitive touch sensor.
I would have plugged that to my power consumption measuring device if the Thingy52 had that.
-Best Regards, MANGO
