Atmel QTouch Library User Guide

o Event System Channel0 (EVSYS_CH0)• The sensor channel number and the relation with X and Y lines strictly follows from thetable provided in the section Table 1.• A rotor /slider sensor can be configured with 3 to 8 channels per rotor or slider dependingon the requirement of the application subject to the total number of channels available inthe library variant selected as listed below.Number of X x Y Maximum Channels per ROTOR_SLIDERchannels4 4 x 1 48 4 x 2 416 4 x 4 416 8 x 2 832 8 x 4 856 8 x 7 864 8 x 8 8• For example, 16 channel libraries with 4X and 4Y lines supports maximum of 4 channelsper Rotor/Slider. But, a 16 channel with 8X and 2Y lines supports maximum of 8channels per Rotor/Slider.• If the lines of the Drive and Receive electrode (X lines or the Y lines) share the samelines with the JTAG, JTAG needs to be disabled. Please check the data sheet to ensurethat 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 bethe 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 ofPORTA with all the combinations of libraries supported. Hence, this needs to beconnected to GND• Proper grounding should be taken care when the controller board and touch sensingboard 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 methoddepends on the configuration. Refer to the Library_Selection_Guide.xls for details.• Vcc should be kept at 4.5V or lower for reliable operationDesign Guidelines for QMatrix acquisition method systemsAVR Microcontrollers can use a number of clock sources, ranging from high precision externalcrystals to less accurate resonators down to simple external RC circuits. Most AVR devices alsocome with integrated RC oscillators. This provides a system clock source without additional costor board space. When using internal RC oscillators some considerations need to be taken. Theaccuracy i.e. frequency of CMOS RC oscillators will vary slightly from device to device due toprocess variance.QMatrix acquisition method uses an internal timer to measure the discharge time of a capacitor,and any frequency variation or fluctuation in the RC Oscillator will thus show up as a variance inthe measurement data. The application should for this reason be designed and tuned to allow forsuch variance in the internal RC oscillator frequency. For most AVR microcontrollers, the ratedaccuracy of the internal RC oscillator is 2%, and to have some headroom and guarantee a robustand stable system, the designer should aim to follow these design rules:‣ Reference Value should be in the 150-300 range‣ Typical delta when touched should be at least 10% of the Reference Value47