DM183026-2 Microchip Technology, DM183026-2 Datasheet - Page 17

• Manufacturer Part Number: DM183026-2
• Description: KIT EVAL MTOUCH CAPACTIVIE
• Manufacturer: Microchip Technology
• Series: mTouch™r

Specifications of DM183026-2

• Sensor Type: Touch, Capacitive
• Sensing Range: 8 & 12 Buttons/Keys, 2 Sliders
• Interface: I²C
• Voltage - Supply: 5V, USB
• Embedded: Yes
• Utilized Ic / Part: PIC16F, PIC18F, PIC24F, PIC32MX
• Interface Type: USB, I2C, UART
• Operating Voltage: 5 V
• Data Bus Width: 32 bit
• Silicon Manufacturer: Microchip
• Kit Application Type: Sensing - Touch / Proximity
• Application Sub Type: Capacitive Touch
• Kit Contents: 8x Brds, Serial Anaylizer, USB Cable
• For Use With/related Products: PIC16F, PIC24F, PIC18F, PIC32
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

2.1
© 2010 Microchip Technology Inc.
INTRODUCTION TO THE TOUCH INTERFACE
Chapter 2. Demonstration Application
This chapter describes the touch sense application that is preprogrammed on the
PIC16F, PIC18F, PIC24F, PIC24H and PIC32MX microcontrollers, and its general
principles of operation. Topics included in this chapter are:
• Introduction to the Touch Interface
• Individual Touch Sense Demonstrations
For PIC24H and PIC32MX MCUs, touch sensing is achieved using a technique known
as the Capacitive Voltage Divider, which makes use of the ADC module. This technique
is based on successive charging/discharging cycles for sample and hold capacitance
and conversely, sensor plus finger capacitance, which basically creates a voltage
divider. For details, refer the application note, AN1298 “Capacitive Touch Using Only
an ADC (“CVD”)” .
Control of the touch sense features is built on the PIC18F and PIC24F microcontrollers’
on-chip Charge Time Measurement Unit (CTMU) module. The CTMU consists of a
constant current source that charges each touch circuit to a voltage level. When any
additional capacitance is added to the circuit (from the touch of a fingertip, for example),
the fixed current source will now charge the circuit to a lower voltage. This change is
how the microcontroller detects a touch event. For detailed information on the CTMU
module, please refer to the related “Charge Time Measurement Unit (CTMU)” Family
Reference Manual sections, which are available from the Microchip web site.
On the PIC16F CSM Evaluation Board, the on-chip Cap Sense Module (CSM) creates
a relaxation oscillator to perform touch sensing. The period or frequency of the relax-
ation oscillator can be measured, and when the sensor is touched, the frequency will
drop and the period will increase, indicating a touched condition.
The microcontrollers use the CTMU, CVD or CSM to monitor its input channels, which
are in turn, connected to capacitive touch pad sensors on the top layer of the circuit
board.
The evaluation board has four different sensor demonstration boards:
• 8-Key Direct Plug-in Daughter Board
• 12-Key Matrix Plug-in Daughter Board
• 2-Channel Slider Plug-in Daughter Board
• 4-Channel Slider Plug-in Daughter Board
A more detailed description of the evaluation boards’ operation is provided in Chapter
4. “Evaluation Board Hardware”.
2.1.1
The response of the sensor to fingertip touch is influenced by many factors: touch
areas, voltage and current levels, ambient humidity, static buildup, and so on. The
capacitive touch sensing is done by a relative shift in the capacitance due to the addi-
tion of the finger capacitance to the touch sensor. The demonstration code supplied
takes most of the typical environmental factors into consideration. The demonstration
application is very flexible in the sense that it can be modified by the user.
Touch Sensitivity
mTouch™ ADVANCED CAPACITIVE
EVALUATION KITS USER’S GUIDE
DS41385C-page 17