MPR121

Sensors

Freescale Semiconductor

41

5.0

Proximity Baseline Filter Setting

As with the touch detection, the proximity detection also dedicates register sets for baseline filter control. These include the

maximum half delta for rising/falling, the noise half delta for rising/falling/touched, the noise count limit for rising/falling/touched,

and filter delay for rising/falling/touched. Table 41 shows an example setting for proximity sensing, the concept is to have quickest

response on baseline rising (when hand takes away) and slowest response on baseline falling (when hand approaching). Refer

to Freescale application note AN3891 for detailed description on baseline system.

6.0

Electrode Configuration for Proximity Sensing

Same as touch sensing, the proximity sensing requires that the charging current and time for the 13th Proximity Detection

electrode to be properly set. This can be done in 3 ways:

1. Globally setting the AFE Configuration Register (0x5B) and Filter Configuration Register if recent current setting and time

setting is zero.

2. Set by using Eleprox Electrode Current Register (0x6B) and Charge Time Register (0x72).

3. Using Auto-Configuration function to automatically set charge current and charge time for this 13th Proximity Detection

electrode.

It’s recommended that Auto-Configuration is used for design efficiency if proximity sensing works properly in this way. Refer

to Freescale application note AN3889 for details of the Auto-Configuration function.

Table 41. Proximity Baseline Filter Registers 0x36~0x40 (Reset Default: all 0x00)

Register Name

Register Address

Example Setting

ELEPROX Max Half Delta Rising

0x36

0xFF

ELEPROX Noise Half Delta Amount Rising

0x37

0xFF

ELEPROX Noise Count Limit Rising

0x38

0x00

ELEPROX Filter Delay Limit Rising

0x39

0x00

ELEPROX Max Half Delta Falling

0x3A

0x01

ELEPROX Noise Half Delta Amount Falling

0x3B

0x01

ELEPROX Noise Count Limit Falling

0x3C

0xFF

ELEPROX Filter Delay Limit Falling

0x3D

0xFF

ELEPROX Noise Half Delta Amount Touched

0x3E

0x00

ELEPROX Noise Count Limit Touched

0x3F

0x00

ELEPROX Filter Delay Limit Touched

0x40

0x00