AN92584 Datasheet, PDF (29/42 Pages) Ramtron International Corporation – Designing for Low Power and Estimating Battery Life for BLE Applications

Designing for Low Power and Estimating Battery Life for BLE Applications
trackpad sensor array implements capacitive sensing (CapSense). The CapSense block converts the
capacitance of the sensor to a digital quantity, which can be processed by the firmware.
 Firmware processing: The sensor array data from the CapSense block is processed by the application firmware
to detect mouse pointer movements and recognize gestures such as zoom, scroll, rotate, click, double-click, and
so on. This data is sent as an HID report over BLE to the BLE Central device.
 BLE connectivity: The remote control device sends the HID reports to its host typically at a 10-ms connection
interval whenever there is a user activity. However, in the absence of a user activity, this interval should be
increased using slave latency to save power and maintain a BLE connection.
The overall system can be represented as shown in Figure 16.
Figure 16. Remote Control System Architecture
HID Trackpad Remote Control
User Input
Track pad Sensor
Array
BLE Connectivity
Capacitive Sigma
Delta (CSD)
Sensing
CPU- Gesture
Recognition
System on Chip
4.5.2
Remote Control Usage Profile
A typical usage model for the remote control follows:
 If the remote is used for 25 minutes a day, it will be in a low-power state for the rest of the day.
 Out of the total usage of 25 minutes, it is estimated that the user will actively use the remote with intermittent
breaks when the remote is idle. The remote is assumed to be in active use for 80 percent of the time and idle for
the remaining 20 percent of the time.
4.5.3
Application Design for Low Power
The activities that are carried out by the application are as follows:
 Scanning the trackpad
 Processing the trackpad data
 Sending the trackpad report over BLE
 Staying in a low-power mode for the rest of the time
A watchdog timer is used to interrupt the PSoC BLE/ PRoC BLE device periodically to scan the trackpad to detect
user activity. A low current consumption can be achieved by keeping the system in a low-power mode between
interrupts. If an activity is detected on the trackpad, the trackpad is scanned to process the finger movements and to
send the data over BLE to the host device. Thus, the firmware of the remote implements a simple algorithm, as
shown in Figure 17.
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Document No. 001-92584 Rev. *A
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