MICROCHIP - AC103003 - BOARD, CAPACITIVE TOUCH, PIC10F

MICROCHIP - AC103003 - BOARD, CAPACITIVE TOUCH, PIC10F

Product Overview

Touch sensing is fast becoming an alternative to traditional push button switch user interfaces, because it requires no mechanical movement, and it enables a completely sealed and modern-looking design. Expanding beyond the consumer market, touch sensing is beginning to take hold in medical, industrial and automotive applications for reasons such as improved aesthetics, reduced maintenance and lower cost.

Microchip’s Capacitive mTouch Solution is a free and easy method to optimize your touch sensing application using a wide variety of hardware and software resource options.

How it Works

A capacitive touch sensor is a copper pad area created on the surface of a printed circuit board. It creates a parasitic capacitance to ground. When a person touches the sensor, or its covering (plastic, glass, etc.), the person’s finger introduces an additional glass-finger-ground capacitance. That capacitance is in parallel to the parasitic one. As capacitors in parallel are added, a finger approaching the pad will increase the total capacitance. This change is the criteria needed to

detect a touch.

Microcontrollers provide the ability to perform capacitive sensing, decision making, responsive actions and other duties pertinent to the system as well.

Capacitive Touch Implementation

The illustration below shows a simple implementation of a single capacitive touch key. One key capacitive touch can:

• Be used as a on/off, open/close button or other single action user interface
• Act as a proximity sensor – detecting a hand coming close to the sensor
• Enable lower standby power consumption – Trigger an action, like lighting up a display, without a touch
• The schematic is very simple and uses a PIC10F204/6 MCU, a diode, a capacitor and a resistor (see the white sensing square on the PCB).
• Being a microcontroller based solution, capacitive touch can also be used to drive an LED, a buzzer or to communicate with the main processor or the rest of the system. The necessary schematic software is provided in AN1202: Capacitive Sensing with PIC10F.

How to Use the Board

• Connect the USB cable to power the board
• The LED will light up to show a touch or finger detection
• The Jumper J2 enables two Sensitivity levels:
• On the left: Higher sensitivity as a proximity sensor
• On the right: Lower sensitivity as a key
• The scanning rate does not change, therefore the power consumption remains the same in both modes.
• The current can easily be measured using the jumper J4 connections
• If a user leaves his finger on the sensor for a couple of seconds, the MCU will re-calibrate the sensitivity of the key. That auto-calibration feature takes care of temperature or humidity changes as well as a “stuck” button.

Flexibility of the Solution

• The MCU can be reprogrammed using the PICkit 2/MPLAB
• ICD 2 connector. By having access to the source code, it is very easy to change some values or parameters to meet your applications’ specific needs.
• The sensitivity can easily be adjusted to the sense pad size and cover material
• The power consumption can be lowered by reducing the scan rate, leaving the MCU in Sleep mode as much as possible
• The autocalibration feature can be disabled, or the software can make it faster or slower depending on the application needs