CAPTIVATE-METAL

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This chapter of the CapTIvate Technology Guide contains the following sections:

  1. Overview

  2. Getting Started

  3. Software Examples

  4. Hardware

  5. Schematics

  6. Layout

To order a CAPTIVATE-METAL, visit the tool folder.

Overview

Compared to traditional capacitive sensing through plastics or glass, capacitive metal touch is only sensitive to an applied force and for this reason is an excellent choice for harsh or hostile environments where there are liquids, grease, mud or grime present and environments where a user may be wearing gloves. Since the change in capacitance is related to the amount of applied force, it is possible to measure, or sense, the amount of pressure applied. For some applications this may be a useful feature that can be used to create an advanced user input.

Metal Touch PCB

Fig. 301 Metal Touch PCB

The CAPTIVATE-METAL panel uses the deflection in the grounded metal overlay to cause a change in the capacitance between the electrodes below and the metal overlay.

How Metal Touch works

Fig. 302 How Metal Touch works

Key Features

The CAPTIVATE-METAL has the following key features:

  • Demonstrates metal touch capability

    • Basic Touch

    • Button Touch with Force Indication

    • Button Touch with Force Measurement

  • Features:

    • 8 self capacitive electrodes

    • LED numeric display to show force and button press

What’s Included

The CAPTIVATE-METAL comes with the following hardware and software:

Kit Contents

  • 1 CAPTIVATE-METAL Development Board

Block Diagram

The functional block diagram for the CAPTIVATE-METAL is shown below.

Getting Started

This section outlines how to get started.

Note: FR26xx refers to FR2633 and FR2676

Out-of-Box Experience

This out-of-box experience describes how to use the CapTIvate Design Center with the CAPTIVATE-METAL, CAPTIVATE-FR26xx and CAPTIVATE-PGMR modules.

Required Tools

Assumptions

  • This guide assumes that CapTIvate Design Center is already installed on the host PC. For installation instructions, see the CapTIvate Design Center chapter.

Connect Hardware

  1. Connect the CAPTIVATE-FR26xx MCU module and CAPTIVATE-PGMR module together.

  2. Connect the CAPTIVATE-METAL panel to the CAPTIVATE-FR26xx module.

  3. Connect the micro-USB cable between the CAPTIVATE-PGMR programmer PCB and your computer

  4. Verify that LED2 and LED5 (power good LED’s) on the CAPTIVATE-PGMR module are lit, and that LED4 (HID-Bridge enumeration) is blinking.

Click to view a typical board setup.

CAPTIVATE-METAL Demonstration

The CAPTIVATE-METAL panel demonstrates an alternative use of capacitive touch by using the deflection in the grounded metal overlay to cause a change in the capacitance between the electrodes and the metal overlay. Compared to traditional capacitive sensing through plastics or glass, capacitive metal touch is only sensitive to an applied force. For this reason metal touch is an excellent choice for harsh or hostile environments where there are liquids, grease, mud or grime present and environments where a user may be wearing gloves.

CAPTIVATE-METAL CapTIvate Design Center

Fig. 303 CAPTIVATE-METAL CapTIvate Design Center

This panel is configured with the following settings:

  • A 20ms active mode scan period (~50 Hz).

  • A 2 MHz conversion frequency for the metal sensors.

  • A total measurement time of 920us for the CAPTIVATE-METAL Panel.

To demonstrate the features of metal touch panel, the demonstration firmware for the CAPTIVATE-METAL panel must be programmed onto the CAPTIVATE-FR2633 processor PCB. This demonstration firmware features three different operating modes: Basic multiple button touch, Single button touch with force and Single button force sensitivity. During the demonstrations it is possible to view real-time sensor response in the CapTIvate Design Center using the *.ser project file included with the firmware download for the CAPTIVATE-FR2633 processor PCB.

To begin working with this panel, go through the steps for running an example project and open the CAPTIVATE-METAL project.

Basic Button Touch

This is demonstration mode #1 and displays “1d” on the LEDs. In this mode,one or more fingers can be pressed at the same time. The number of buttons pressed is displayed in the left most position of the LED display. The value of button value is displayed in the right most position. If more than one button is pressed the LED display shows the number of buttons and the sum total of the button values.

CAPTIVATE-METAL CapTIvate Design Center

Fig. 304 CAPTIVATE-METAL CapTIvate Design Center

Button Touch with Force Indication

This demonstration is mode #2 and displays “2d” on the LEDs. In this mode, when a single button is pressed, the value of the button is displayed in the left most position of the LED display. Additionally, one to three bars representing the strength of the finger press on the button is displayed in the LED display. This is an example of how the button force information could be used by applications as advanced user input.

CAPTIVATE-METAL CapTIvate Design Center

Fig. 305 CAPTIVATE-METAL CapTIvate Design Center

Button Touch with Force Measurement

This demonstration is mode #3 and displays “3d” on the LEDs.

In this mode, when a single button is pressed, the value of the button is displayed in the left most position of the LED display. Additionally, the measured change in capacitance, expressed as a delta measurement count, is displayed in the LED and represents the strength of the finger press.

CAPTIVATE-METAL CapTIvate Design Center

Fig. 306 CAPTIVATE-METAL CapTIvate Design Center

Changing the Demonstration Mode

After the initial programming of the demonstration firmware, no re-programming is required to switch demonstration modes. The demonstration modes can be easily changed using the steps outlined below. The operating mode is stored into the MSP430FR2633’s non-volatile FRAM memory and is not affected by reset or power cycle.

CAPTIVATE-METAL CapTIvate Design Center

Fig. 307 CAPTIVATE-METAL CapTIvate Design Center

Hardware

The CAPTIVATE-METAL consists of a 2-layer, 1.6mm thick FR4 printed circuit board with a Stainless Steel overlay and acrylic base substrate.

Sensor Design and Organization

The PCB’s 8 electrodes are connected to CAP0.0, CAP1.0, CAP2.0, CAP3.0, CAP0.2, CAP1.2, CAP2.2 and CAP3.2 surrounded by a solid ground plane on the sensor layer (top) and hatched ground on the backside (bottom) layer. The Altium design files for this project can be found at https://www.ti.com/tool/captivate-metal

pcb

Fig. 308 pcb

Metal Stackup

This demonstration panel is constructed using a 301 SS Gauge 31 (0.25mm) metal overlay bonded to the PCB using 2 layers of thermal bonding adhesive TBF583 film by 3M (total thickness = 0.1mm).

pcb

Fig. 309 pcb

The bonding adhesive is die cut with 22mm holes to accomodate the 20mm electrode pads on the PCB as shown in the diagram.

pcb

Fig. 310 pcb

Three pogo-posts located on the PCB ensure a grounded contact with the metal overlay when it is bonded to the PCB. The PCB and overlay assembly is bonded to a 5mm thick acrylic base. Vias in the middle of each sensor pad and holes in the acrylic base provide venting to the atmosphere.

For more information about designing metal touch applications, refer to the Design Guide chapter, section on Metal Touch

Schematics

CAPTIVATE- Schematic

Fig. 311 CAPTIVATE- Schematic

Layout

PCB Top Layer

Fig. 312 PCB Top Layer

PCB Bottom Layer

Fig. 313 PCB Bottom Layer

PCB

Fig. 314 PCB