Wires for Capacitive sensor prototype

[Nimra Jalali]

Hi,

I am working on building a small prototype for capacitive touch sensing. I have had the wires in the attached image passed on by another colleague long time ago. They are really resilient to noise and hence I would like to know if anyone know where to get more from? They are overall 0.5 mm thick (not sure about core thickness and guess it is single core). The outer insulation is clear. I have found other cables wobble and causing noise signals. These are really good in that aspect. I don't know if it is because they are single core and outer insulation is denser than regular PVC.

Please let me know if you know of this.

Best Regards
N.

 

[Harald Kapp]

I do not have a source for your special cable, sorry.

The "noise" you get is probably from using single wires. The distance between the wires can change through moving wires and with distance changes capacity - a no go for a capacitive sensor. You should be able to use any cable with 2 wires (where the distance between wires can't change). I recommend you use twisted-pair cable to minimikze sensitivity to magentically coupled noise. For additional protection against electric noise use shielded (twisted-pair) cable and connect the shield to GND of your setup.

The wires you use probably produce little "noise" due to their stiffness which keeps them in place, so noc change in distance and capacitance due to moving wires happens.

 

[Nimra Jalali]

Thanks Harald, I appreciate your help. I would like to also know if there are any size limitations to designing the sensing electrodes when it comes to both self-capacitance and mutual capacitance. The reason I am asking this is because my project aims at counting foot step using capacitive detection. The detectable area is considered to be of 30 cm x 30 cm. I am trying to understand which mode of sensing (self or mutual?) is more applicable considering the size of the sensed area.

Best Regards
N

 

[Harald Kapp]

I couldn't tell you that. It should be easy to try both modes (I guess most capacitive sense chips support both modes) and select the one working best.