FT5206 Waveform Capture
In the following waveform captures channel 1 (yellow) is connected to RX1 of the FT5206 and channel 2 (blue) is connected to TX15. Note that the captured waveforms are a bit noisy, probably because of the test setup where ~50mm wires were soldered to the connector of the touch panel. Using a ground spring and probing directly on the contact would result in a better waveform but the functional behavior is still visible here.
Note that the waveforms shown here are from one of the many firmwares the FT5206 can be running. This is using a binary filed called "ft5206-sc3037-800X480.bin".
In this capture we can see that the value RX1 is the same during the period where TX15 is active as it is before. This is the expected behavior.
No Touch
The voltage level of RX1 is dropping here as the touching finger is interfering with the electric field between TX15 and RX1.
Touch On Column 15, Row 1
Similarly, when touch column 14 the part before TX15 is active is affected. This is where TX14 is active -> column 14.
Touch On Column 14, Row 1
Same as before but now touching column 13 instead.
Touch On Column 13, Row 1
This waveform shows the period where TX15 is active. The signal is toggling 34 times between 0 and ~5.8V. This indicates that there is some kind of boost circuitry inside the chip as the power supply is only 3.3V.
TX15 Active
While testing I noticed that the controller is switching between two different modes. When a touch is present it samples the rows more often than during the idle period. During idle the duty cycle is around 13% and when a touch is present it increases to 44%.
The controller stays in the active mode for 10s after the touch is removed as can be seen in the last waveform.
Idle Mode
Active Mode
Time to idle
Because there are 9 separate row signals that can be read at the same time and 15 columns that are scanned, it is possible to detect multiple fingers. In the waveforms below RX6 is shown as purple. The first shows with no touch and the second shows one finger touching (column 15, row 1) and another touching (column 13, row 6). To separate between which finger is which there has to be some clever algorithm.
RX6, RX1, TX15 - No touch
RX6, RX1, TX15 - Dual touch