QT115

The QT115 is a variant of the QT110 having variable sensitivity and the ability to daisy-chain, allowing multiple QT115's to be used in immediate proximity to each other to create a small touch panel of up to 10 keys. Like the QT113, it has a variable threshold which can be modified by simply altering the value of the sample capacitor Cs, which acts to modify gain. It does not include any of the option jumpers found on the QT110 or QT113; instead it has a single option jumper for 'Master' or 'Slave' mode operation.

The QT115 includes 'Sync Out' and 'Sync In' pins for daisy-chaining. The first IC in the chain is the Master while the remaining devices in the chain are slaves. Daisy-chaining lets each device take its turn in generating a burst, free from interference by the other QT devices. In Master mode the IC operates autonomously, and generates a 20us negative Sync Out pulse on pin 3 after each burst. In Slave mode the IC issues a detection burst only after it receives a negative Sync pulse on pin 4 from a prior device in the chain, which could be another Slave or a Master. Slave devices in turn issue a 20us Sync pulse after each burst on pin 3.

The QT115 is designed for contact and prox sensing applications where high sensitivity is paramount, for example when sensing through thick panels or windows or for security monitoring. The QT115 trades off power consumption for speed and sensing range. Also, note that the device has a consensus filter count of 3 instead of 4, and does not have the drive capability for a piezo 'beeper'.

If desired, the QT115 can be eliminated and the chain of Slave devices can be mastered from an external pulse source of 20us negative pulses at the desired repetition rate. This potentially allows for faster operation.