Freescale Semi

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  • Capacitive and Resistive Touch Sensing Application

  • Created: Mar 09, 2015

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There are different types of screens embedded to consumer electronic devices in which some of them are now touch gesture enabled. The touch gesture enabled display or commonly called as touchscreen provides convenience to users in which data manipulations and interaction are much faster compared to devices using typical controllers. Due to the market demand, several manufacturing industry are now in mass production of touchscreen display that signifies visual display improvements are now expected to electronic devices. This circuit design features a simple touch-sensing application. It is capable of resistive touch screen that uses X and Y coordinates calculation with built-in filter to improve stability. It also uses four capacitive keys in different configurations such as rotary, slider, and keypad. The communication ports are both available in UART and I2C. The system can operates in three modes such as normal run mode, sleep mode, and shutdown mode that saves energy.

The circuit is comprised of CRTOUCHB10VFM 32-pin Xtrinsic Touch-Sensing Platform that is design to serve as a four wires and five wire resistive touch driver, and capacitive touch sensing device. The MK02FN64VLH10 100 MHz Cortex-M4 Based Microcontroller with Floating Point Unit (FPU) is used as host controller. The capacitive touch and resistive touch are provided for user interaction that also serves as the touch sensors of the entire system. The resistive touch uses pressure for sensing while capacitive touch uses electrostatic field distortion that produces measurable change in capacitance. The capacitors are used to minimize distortions in supplies. The resistors are used as limiters and pull-ups. The SPST switch is used to control selection of setups and configurations in UART and I2C communications.

The migration of visual display medium is now noticeable that most of the electronic devices with display are now touchscreen. This design can serve as a reference for the development of touchscreens that is used in different electronic products including industrial and commercial equipments. Due to its flexibility, there will be several applications of this designed system.



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