PICDEM™ TOUCH SENSE 2 DEMO
BOARD USER’S GUIDE
©
2008 Microchip Technology Inc.
DS51748A-page 11
Chapter 2. The Demonstration Application
This chapter describes the demo touch sense application that is preprogrammed on the
PIC24F microcontroller and its general principles of operation. Highlights include:
• Introduction to the Touch Interface
• Individual Touch Sense Demonstrations
2.1
INTRODUCTION TO THE TOUCH INTERFACE
Control of the touch sense features are built on the PIC24F microcontroller’s on-chip
Charge Time Measurement Unit (CTMU) module. The CTMU consists of a constant
current source that charges the touch circuit to a fixed voltage level. When any addi-
tional 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. A more detailed description of the CTMU’s
operation is provided
Section 11. “Charge Time Measurement Unit (CTMU)”
of the
“
PIC24F Family Reference Manual”
(DS39724).
The microcontroller uses the CTMU to monitor its analog input channels, which are in
turn, connected to capacitive touch pad sensors on the top layer of the circuit board.
The acrylic top layer protects the top layer of the PCB from direct contact, as well as
visual cues of where to touch.
The Touch Sense 2 Demo Board has four different sensor demonstration areas:
1.
Directional Keypad (bottom) and Display (top)
2.
Numeric Keypad
3.
Touch Slider
4.
“Soft” Power Control
A more detailed description of the Touch Sense 2 Demo Board’s operation is provided
in
Chapter 4. “Demo Board Hardware”
.
FIGURE 2-1:
TOUCH SENSE AREAS ON THE TOUCH SENSE 2 BOARD
Programmer
USB
1
2
3
4
