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  • AT03030 Q Matrix Touchpad 2D Position Tracking

  • Created: Apr 05, 2017

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The design is a Qmatrix touch sensor for 2D position tracking application. Touchpad operates either capacitive sensing or resistive sensing depending on the technology used. The design uses a capacitive sensing touch sensor that measures mutual capacitance between two electrodes. The design is a low resolution touchpad, that is up to a maximum resolution of 400dpi. It has a single tap detection that supports single finger operations.

The design uses the ATxmega16D4 microcontroller for the design. The touchpad design comprises of 56 touch sensor organized using 8 X lines and 7 Y Lines. Qmatrix touch sensor require X+2Y+2 general purpose I/O pins for realization. It uses 8 I/O pins for X lines, 14 I/O pins for Y line, and 2 I/O pins for sampling pin and analog ground. Two LEDs are used to indicate the single tap and touchpad state. These LEDs are driven by BC847B Transistor. The state of the transistor is controlled and connected by the ATxmega16D4 GPIO pin. LED1 is configured for single tap indication. This is set to operate in toggle mode. LED1 turns ON when single tap event is detected first time and OFF in the subsequent single tap detection. LED2 is configured to indicate touchpad active status. This LED will be in ON as long as there is a touch. Serial communication using USART interface is used to display the touchpad X-Y position on HyperTerminal of host PC. USART_TX and USART RX is connected to PD3 and PD2 respectively. Touch data is transmitted using QDebug protocol through Bit Bang SPI interface. QT600 USB Interface Bridge is used to transmit touch data to QTouch Analyzer. The circuit can be powered by a +5V external supply from the USB connection. A +3.3V regulator is used to regulate the the supply from the USB connection. The +3.3V supplies the microcontroller and other peripherals.

The design maybe limited to 400dpi and single touch operation, but the technology has evolved with many great features and higher resolutions. They are commonly seen in laptops, that is used as substitute for a mouse.