I would like to know the limitation and maximum sensing distance of the capsense proximity sensing loop design.
1. Is the sensing distance proportional to the size and trace width of the sensing loop?
We would like to say that the limitation is not the sensing distance but the parasitic capacitance and change in parasitic capacitance of the proximity sensor. The recommended maximum parasitic capacitance of sensor is 200 pico farads. This is not a strict value as you can always do manual tuning of sensors.
2. Is there any limitation about the sensing loop size?
Again, there is no limitation in size. The limitation is due to parasitic capacitance and environmental noise factors.
The maximum evaluated sensing distance is 30 cm using proximity sensor. This was in a well tuned hardware with firmware filters enabled.
The sensing distance is proportional to the size of the loop. Roughly, we can expect a sensing distance equal to the diameter in the case of circular loops and equal to the diagonal in the case of rectangular sensors. The trace width is recommended to be 1.5 mm as anything greater will only increase the Cp without any performance gains.
What is the proximity sensing distance that you are targeting in your application? What is the size of the PCB?
It is recommended to place the sensor loop around the periphery of the PCB so that you get maximum sensing distance. Note that a ground ring needs to be placed around the proximity sensor for noise reduction.
Thanks for your info and detail explanation.
I was thinking to create a proximity sensor for around 100cm distance with around 25cm diagonal.
I am fine with the GND ring around the sensor, but you mentioned it probably can create up to 30cm, plus with a well tuned design. Do you have any detail about this type of design to get more detail understanding with it.
Any additional concern I may need to pay attention? Please advise.