CAPTIVATE-METAL¶
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This chapter of the CapTIvate Technology Guide contains the following sections:
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.
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.
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
The latest CapTIvate Design Center PC GUI Tool must be installed on a host PC, Mac, or Linux machine
A CAPTIVATE-FR2633 or a CAPTIVATE-FR2676 programmed with the CAPTIVATE-METAL-Demo firmware example
A CAPTIVATE-PGMR module is required for programming and communication with the host PC
A micro-USB cable is required to connect the CAPTIVATE-PGMR to the host PC
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
Connect the CAPTIVATE-FR26xx MCU module and CAPTIVATE-PGMR module together.
Connect the CAPTIVATE-METAL panel to the CAPTIVATE-FR26xx module.
Connect the micro-USB cable between the CAPTIVATE-PGMR programmer PCB and your computer
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.
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.
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.
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.
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.
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
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).
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.
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
