4.2.1.3 Approach Detection
Approach Detection is an embedded power-saving feature of Microchip’s Colibri Suite. It sends MGC3140 to Sleep mode and scans periodically the sensing area to detect the presence of a human hand. Utilizing the built-in Self Wake-up mode, Approach Detection alternates between Sleep and Scan phase. During the Scan phase, the approach of a human hand can be detected while very low power is consumed.
A detected approach of a user exceeding configured threshold criteria will alternate the MGC3140 from Self Wake-up to Processing mode or even the application host in the overall system.
Within the Approach Detection sequence, the following scans are performed:
- Approach Scan
- An Approach scan is performed during the scan phase of the device’s Self Wake-up mode. Typically, one Rx channel is active but more channels can be activated via the GestIC Library. The time interval (scan interval) between two consecutive Approach scans is configurable. For typical applications, the scan cycle is in a range of 20 ms to 150 ms. During the Approach scan, the activated Rx channels are monitored for signal changes which are caused by, for example, an approaching human hand and exceeding the defined threshold. This allows an autonomous wake-up of the MGC3140 and host applications at very low-power consumption.
- AFA Scan
- During Wake-up-on-Approach, periodic Automatic Frequency Adaptation (AFA) scans are performed. During this scan, the environmental noise is measured and a new Tx frequency will be selected from the five preset frequencies available, if necessary. The AFA scan is usually performed in configurable intervals from 120s to 600s (120s typical). The timing sequence of the Approach Detection feature is illustrated below:
