Touchkey matrix

AN3236

10/15

DocID17613 Rev 3

3.2

Software implementation

Channel acquisition is managed by the touch sensing firmware library in the same way as

for single electrodes. A decoding step must be also performed at application level

depending on the combination of detected channels.

A touch on touchkey 1 triggers a detection on two channels, Ch1 and Ch4 (see Figure 4:

Matrix hardware implementation example).

The decoding table mirrors the matrix shown in Figure 4. A touchkey is activated when the

two channels it is connected to are in detection state.

3.3

Limitation

For such a touchkey matrix, one or several touchkeys can be touched simultaneously on the

same row or the same column. As shown in Figure 5, touchkey 1, 4, 7, and 10 are touched

simultaneously and can be decoded without ambiguity.

Figure 5. Decodable multi-touch example