Qvar sensing - questions

[kSun.1]

I am very interested in this Qvar sensing.

1. What i understand is this Qvar depends on the electrode discharge and the Qvar wants to take advantage of ESD, is it correct?
2. Also does the Electrode sensing pad size affect sensing ability?
3. How could we protect the pins/chip? Do we always need ESD Diode to protect the Chip ?

[Eleon BORLINI]

Hi @kSun.1​ ,

I see your post also on this other post, thank you from ST for the appreciation.

The ESD diode are mandatory to protect the QVAR lines from electrostatic and electromagnetic discharges that goes beyond the absolute maximum rating that the QVAR can withstand. The dimension of the electrode pad affects the "wireless" electric field sensing, while it is pretty negligible for the QVAR contact sensing.

-Eleon

[kSun.1]

Hi Eleon,

Great, thanks a lot for replying. a few more questions to bother you:

1. Is wireless electric field sensing based on electrostatic induction? while contact sensing is based on electrostatic discharging?
2. I saw the eval kit STEVAL-MKI228KA, why the electrode designed in such way that Q+ and ground should be touched the same time? 

[Eleon BORLINI]

Hi @kSun.1​ ,

basically "yes" at both questions 🙂

-Eleon

[kSun.1]

Hi @Eleon BORLINI​ 

Thanks.

For question 2, can you explain a little bit why Q+ and ground should be touched the same time? 

[kSun.1]

Also @Eleon BORLINI​ 

1. What is the difference between this Qvar tech and Capacitance sensor(link below)?

 For capacitance sensor, the finger NOT have direct contact to the sensor. The capacitor is covered by solder mask or etc.. But Qvar, it could happen, fingers can directly contact Q+ and GND.

https://www.allaboutcircuits.com/technical-articles/introduction-to-capacitive-touch-sensing/

2. If I glue the Qvar electrode sensor under a piece of plastic, my finger only touch the plastic. In this case, I don't touch the sensor directly, will the Qvar works as the same as capacitance sensor?

Thanks a lot