QMatrix acquisition method libraries are available for a set of AVRs The library variants can be configured to have port and pin assignments for X, Ya, Yb and SMP.
Some of the key constraints are
The QMatrix acquisition method libraries internally use TIMER1 for the operation,
TIMER1 will not be available for critical sections of the code where the library is called. But resources are available to the host application when the normal user’s application is running.
In case of XMEGA™ devices, the resources are used internal to the library and hence cannot be used by the host application
The sensor channel number and the relation with X and Y lines strictly follows from the table provided by #QT_SQ_LIB.SECTION_OSZ_YTO_AG.XML__TABLE.1.
A rotor /slider sensor can be configured with 3 to 8 channels per rotor or slider depending on the requirement of the application subject to the total number of channels available in the library variant selected as listed below.
|
Number of channels |
X x Y |
Maximum Channels per ROTOR_SLIDER |
|---|---|---|
|
4 |
4 x 1 |
4 |
|
8 |
4 x 2 |
4 |
|
16 |
4 x 4 |
4 |
|
16 |
8 x 2 |
8 |
|
32 |
8 x 4 |
8 |
|
56 |
8 x 7 |
8 |
|
64 |
8 x 8 |
8 |
For example, 16 channel libraries with 4X and 4Y lines supports maximum of 4 channels per Rotor/Slider. But, a 16 channel with 8X and 2Y lines supports maximum of 8 channels per Rotor/Slider.
If the lines of the Drive and Receive electrode (X lines or the Y lines) share the same lines with the JTAG, JTAG needs to be disabled. Check the data sheet to ensure that there are no conflicts between the X/Y lines and JTAG lines used for the device.
YB line for a particular device cannot be changed and it has to be the configured to be the ADC port of the selected device.
The AIN0 pin of the device needs to be connected to the GND.
In case of XMEGA devices, the reference pin for input to analog comparator is Pin7 of PORTA with all the combinations of libraries supported. Hence, this needs to be connected to GND
Proper grounding should be taken care when the controller board and touch sensing board are different.
The channels used for an individual rotor or slider should all be on the same Y line.
The maximum number of Rotors / Sliders supported by the QMatrix acquisition method depends on the configuration. Refer to the Library_Selection_Guide.xls for details.
Vcc should be kept at 4.5V or lower for reliable operation