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This chapter of the CapTIvate Technology Guide contains the following sections:
To order a CAPTIVATE-METAL, visit the tool folder.
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.
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.
The CAPTIVATE-METAL has the following key features:
Demonstrates metal touch capability
Button Touch with Force Indication
Button Touch with Force Measurement
8 self capacitive electrodes
LED numeric display to show force and button press
The CAPTIVATE-METAL comes with the following hardware and software:
1 CAPTIVATE-METAL Development Board
The functional block diagram for the CAPTIVATE-METAL is shown below.
This section outlines how to get started.
Note: FR26xx refers to FR2633 and FR2676
This out-of-box experience describes how to use the CapTIvate Design Center with the CAPTIVATE-METAL, CAPTIVATE-FR26xx and CAPTIVATE-PGMR modules.
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
This guide assumes that CapTIvate Design Center is already installed on the host PC. For installation instructions, see the CapTIvate Design Center chapter.
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.
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.
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.
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.
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
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).
The bonding adhesive is die cut with 22mm holes to accomodate the 20mm electrode pads on the PCB as shown in the diagram.
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