Is it possible to make sensing distance 5cms using PCF8883 evaluation board (OM1105) nad external plate

[vijayendrakumar]

Hi All, 

I am trying to achieve a sensing distance of around 4~5 cms using PCF8883 on OM11055 eval board. I am attaching an external sensing plate of area around 4"x4". I followed steps  form UM10370 like cutting the CP1 connection etc...

But what I am observing is whole PCB is turning sensing to touch.

What should be optimal component values(CCPC,CCLIN ,RC etc.) for this sensing distance . I am on a tough timeline for this project .So Request your urgent help.

Regards,

Vijayendra

[darioarias]

Hi Vijayendra,

If the whole board is turning sensitive to touch, you might need to readjust the sensitivity of the board, also remember that they recommend to use coax cable to use an off board sensing plate. I wonder if you follow this recommendations. Besides, it is recommended to cut the trace shorts on the underside of the PCB at J4 and J5 so you can add conventional through-hole passive components of different values.

I have two documents that I highly recommend to check:
The application note AN3863 explains in detail how to design Touch Sensing Electrodes and the application note AN10832 explains how to choose Rc, Ccpc and Cclin. to adjust the sensor sensitivity and sampling frequency.

Regards,

Dario