at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 42

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

5.5
42
Detect Integrators – NDIL, FDIL
AT42QT1481
The NDIL parameter is used to enable and disable keys in the matrix and to provide signal
filtering. To enable a key, its NDIL parameter should be nonzero (NDIL = 0 disables a key).
To suppress false detections caused by spurious events like electrical noise, the QT1481
incorporates a detection integrator or DI counter mechanism. A per-key counter is incremented
each time the key has exceeded its threshold and is decremented each time the key does not
exceed its threshold. When this counter reaches a preset limit the key is finally declared to be
touched.
The DI mechanism uses two counters. The first is the fast DI counter FDIL. When a key's signal
is first noted to be below the negative threshold, the key enters 'fast burst' mode. In this mode
the burst is rapidly repeated for up to the specified limit count of the fast DI counter. Each key
has its own counter and its own specified fast-DI limit (FDIL), which can range from 1 to 15.
(FDIL = 0 is invalid; do not use).
When fast-burst is entered the QT1481 locks onto the key and repeats the acquire burst until the
fast-DI counter reaches FDIL or drops back to zero. After this the QT1481 resumes normal
keyscanning and goes on to the next key.
The Normal DI counter counts the number of times the fast-DI counter reached its FDIL value.
The Normal DI counter can only increment once per complete scan of all keys. Only when the
Normal DI counter reaches NDIL does the key become formally active.
The net effect of this is that the sensor can rapidly lock onto and confirm a detection with many
confirmations, while still scanning other keys. The ratio of fast to normal counts is completely
user-settable via the Setups process. The total number of required confirmations is equal to
FDIL times NDIL.
Disabling a key: If NDIL = 0, the key becomes disabled. Keys disabled in this way are pared
from the burst sequence in order to improve sampling rates and thus response time. See
Section 2 on page
This function is programmed on a per-key basis. Do not use FDIL = 0 because it is invalid.
NDIL Typical values:
NDIL Default value:
FDIL Typical values:
FDIL Default value:
• If FDIL = 6 and NDIL = 2, the total detection confirmations required is 12, even though the
• If FDIL = 1, the QT1481 functions conventionally. Each channel acquires only once in
• If FDIL >2, then the fast-DI counter also operates in addition to the NDIL counter.
• If Signal <NTHR: The fast-DI counter is incremented towards FDIL due to touch.
• If Signal >NTHR then the fast-DI counter is decremented due to lack of touch.
QT1481 only scanned through all keys only twice. The DI is extremely effective at reducing
false detections at the expense of slower reaction times. In some applications a slow reaction
time is desirable. The DI can be used to intentionally slow down touch response in order to
require the user to touch longer to operate the key.
rotation, and the normal detect integrator counter (NDIL) operates to confirm a detection.
Fast-DI is in essence not operational.
6.
2, 3
2
4 to 6
5
9621B–AT42–06/11