SLAA842B December 2018 – August 2019 DS90C401 , DS90C402 , MSP430FR2512 , MSP430FR2522 , MSP430FR2532 , MSP430FR2533 , MSP430FR2632 , MSP430FR2633 , MSP430FR2672 , MSP430FR2673 , MSP430FR2675 , MSP430FR2676
The second step of designing a successful capacitive touch sensing system is to define the system requirements and the operating conditions of the end product. This is a critical step to ensure the desired performance in the product. In many cases, there are unique areas of expertise within a company, with separate groups or teams that implement each function. Sometimes one or more of these functions may even be outsourced to a third-party developer or contract manufacturer. Therefore, it is strongly recommended to have all the function teams working together. Table 2 lists several key system requirements and operating conditions to consider when defining a product with CapTIvate technology. You might not have all the answers for these requirements at this step of the design process, but the overall design process is more efficient with more requirements being defined early.
| Requirement | Description |
|---|---|
| Memory configuration | Estimate the memory requirements based the functions implemented on the MCU. Refer to Memory Configuration Considerations. |
| Pin counts | Estimate the number of GPIOs based on the application. CapTIvate capacitive touch sensing MCUs support up to 19 GPIOs. |
| Packages | Define the package that is suitable for the application. CapTIvate capacitive touch sensing MCUs are available in QFP, TSSOP, QFN, and DSBGA packages. |
| Communication interface | Define the type and number of communication interfaces that the device need to support. CapTIvate capacitive touch sensing MCUs support I2C, UART, and SPI interfaces. |
| Bootloader | Define if the application requires bootloader for programing during the prototyping phase, final production, and in service. |
| Supply voltage range | Determine supply voltage range for MSP430 MCU provided by system. |
| Additional peripherals | Define additional peripherals required for the application such as ADC, timers, and comparators. |
| Number of CapTIvate I/Os | This number depends on the capacitive sensor requirements. Refer to CapTIvate Device Selection. |
| Number of CapTIvate blocks | Each CapTIvate block has 2 or 4 CapTIvate I/Os depends on the part. The number of CapTIvate measurement blocks on a device determines the number of sensing electrodes that can be measured simultaneously. CapTIvate MCUs have 1, 2, or 4 CapTIvate blocks depends on the device. Select a device with more blocks if the application includes many capacitive sensors and has strict power consumption and response time requirements. Refer to CapTIvate Device Selection. |
| Requirement | Description |
|---|---|
| Function | The functionality of the capacitive sensor in the application (human detection, object detection) |
| Type | The type of the capacitive sensor in the application (button, slider, wheel, proximity, metal touch) |
| Quantity | The number of each type of the sensors. |
| Size | The dimension of each type of the sensors based on the desired touch area and the space constraints |
| Resolution | The resolution of the slider, wheel, and proximity sensors |
| Shape | The shape of each type of the sensors based on the desired touch area and the space constraints |
| Material | The material of the sensors (PCB, FPC, conductive wire, copper foil, ITO) |
| Sensor orientation | The orientation of the capacitive touch sensors (vertical, horizontal) |
| Requirement | Description |
|---|---|
| Overlay properties | Properties of the overlay on top of the capacitive touch sensors including material, thickness, stackup, and bounding |
| Enclosure properties | Properties of the enclosure for the system including material, thickness, stackup, and bounding |
| PCB interconnection | Interconnection between different PCBs in the system |
| Requirement | Description |
|---|---|
| Power supply | System power supply configuration (wall power, battery power) |
| Indoor or outdoor | Operating environment for the application |
| Temperature variance | Temperature variance on the CapTIvate MCU including the rate of change and the range of the expected temperature condition |
| EMC performance | Type and stress level of EMC tests that the system must pass |
| Moisture and liquid performance | Expected response of the capacitive touch sensors under the typical liquid scenarios of the application. |
| Power consumption | Targeted average and transient power consumption from the MSP430 MCU |
| System noise | Potential noise sources in the system |
| Feedback | User feedback associated with the detection (LEDs, buzzers, haptic) |