Sync/Sleep
This input performs two functions: wake-up from sleep input, or noise synchronization input.
Wake from Sleep via UART
: Link this input to the Rx line to enable wake from sleep via UART. In this mode,
the device will wake when a dummy transmission (a null byte) is received from the host over the UART RX
line. The logic level change of the UART RX line is used to create a wakeup logic input to the chip’s WS pin.
Wake from Sleep via SPI
: Link this input to MOSI to enable wake from sleep via SPI. In this mode, the device
will wake when a dummy transmission (a null byte) is received from the host over the SPI lines. The logic level
change of the MOSI line is used to create a wakeup logic input to the chip’s WS pin.
External Wake from Sleep:
Feed a minimum 5us sync pulse (normal logic high, pulse low) to pin 13 of J1 with
respect to GND to wake the part from a sleep state.
External Noise Sync
: Feed a TTL or 5V CMOS synchronization pulse into pin 13 of J1 with respect to GND.
The QT60486 / QT60326 acquisition bursts can be synchronized to an external source of repetitive electrical
noise, such as 50Hz or 60Hz using the Noise Sync feature, which is enabled via Setups. External repetitive
signals are thereby heavily suppressed, since the system and the noise become synchronized and no longer
beat or alias with respect to each other. The sync input triggers the burst for key 0 (X0Y0); the device waits for
the sync signal for up to 100 ms after the end of a preceding full matrix scan (after key #47), then, when a sync
pulse is received, the matrix is scanned in its entirety one time. If no sync pulse is received in 100ms, the part
wakes on its own and re-scans the matrix one time then goes back to sleep. Sync pulses should be spaced no
more than 99ms apart to prevent this from happening.
Reset / Recal Button
This button causes a hard reset and a recalibration of all keys. The recalibrate button in QmBtn™ will also
accomplish a recalibration of all or some keys depending on current Scope. It is also possible to cause a hard
reset via QmBtn™.
Oscilloscope Sync
The ‘scope sync’ test point can be used to synchronize an oscilloscope. When enabled in QmBtn™, this signal
provides a pulse that brackets the chosen burst or bursts, making diagnostics much simpler. With the scope
sync enabled for one key, the X matrix drive signals can be clearly seen.
Status LED
The LED shows touch and error activity. If there is a calibration error or another type of fault, this LED will glow
solid. 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.
Cs Capacitors
The Cs capacitors, C12, C13, C14, C15, C17, C18 are the charge integrators that are used to detect changes
in key capacitance. Corresponding resistor network RN8 is used to convert the acquired charge to digital form.
These parts are optimal and should not be changed in value without a known reason.
