back to sleep. Sync pulses should be spaced no more than 49ms apart to prevent this
from happening.
The most common type of noise is power-line related. If there is a lot of random signal
noise on the keys (consistently more than +/- 4 counts), consider using this feature to
eliminate the noise.
Noise can also be overcome by additional Detection Integrator filtering, or by increasing
both Burst Length and the Threshold levels.
Dwell Time Potentiometer
This pot controls the delay from the rising edge of an X drive to the release of the sample
gate on a selected Y line. This feature controls the acceptance time of the sampled
charge, and can be used to suppress the effects of moisture on the touch panel. Circuits
do not normally require a potentiometer but it is provided so that you can experiment with
its effect.
The normal span of the pot is from 80ns to 2us. It must be adjusted using an oscilloscope
probing on both an X line (test point XS, located below the QT60xx5) and the Y gate
signal (YE, located next to U2 below the QT60xx5). Trigger on XS and display both XS
and YE, and adjust the time between the rise of XS and the following edge of YE.
Reset / Recal Button
This button causes a reset and thus a recalibration of all keys. Pushing this button will
normally act to center the signals and reference levels. The recalibrate button in QmBtn
will also accomplish a recalibration of all or some keys depending on the Scope setting
located above it. The reset button in QmBtn will cause a hard reset of the QT60xx5.
UART LED
The UART LED indicates activity on the UART lines from the host (i.e. the PC)
SPI LED
The SPI LED indicates activity on the SPI lines to the QT60xx5. When using the RS2323
communications mode, both the SPI and UART LEDs will flash at the same time.
STATUS LED
The Status LED is driven from the QT60xx5 and shows key and error activity. If there is a
calibration error or another type of fault, this LED will glow solidly. If the part is working
normally, and no keys are detecting, the LED will be off. If one or more keys are touched,
the LED will flicker. The brightness of the flicker will be proportional to the number of keys
detecting.
E664/R1.0 03/02
