Calibration and Drift Compensation

Calibration and drift compensation operate similarly to the QT110. With large values of Cs and small values of

Cx, drift compensation will appear to operate more slowly than with the reverse. Note that the positive and

negative drift compensation rates are different; the sensor will compensate more quickly for the removal of an

object than it will to the introduction of an object.

The QT1115 uses a fixed recalibration timeout of 10 seconds.

The QT115's response time is entirely dependent on the burst rate. In Master mode the nominal burst rate is

40ms, and 3 successive bursts are required to confirm a detection, giving a nominal 120ms response time.

In slave mode, the burst rate and hence response time are dependent on the input sync pulse rate. Faster sync

pulse rates will lead to faster response times.

The QT115's HeartBeat pulse works exactly the same as in the QT110 except that the HeartBeat rate is the

same as the burst rate. In Master mode, the HeartBeat signal occurs just before the acquisition burst. In slave

mode, it occurs just after receipt of the slave pulse on pin 4.

As with the QT110, the HB signal can be

suppressed if not wanted by a variety of simple methods.

The QT115 is intended to be daisy-chained for the purpose of allowing each of the sensors to operate without

interference from other devices in the chain. This allows electrodes from each device to be placed immediately

adjacent the other electrodes with only the barest of gaps.

Individual devices in the chain can have unique sensitivities. QT113-style sensing allow for very high sensitivity

levels if required. One device can be used with a large metal area to create a prox detector capable of many

centimeters range, for example to activate the panel, equipment, or a light upon a mere hand-wave. The other

devices in the chain can be used to implement low-gain touch switches that must be contacted by a fingertip for

activation. The net effect of this configuration can be quite dramatic.

The only limitation is that the sum of the burst lengths, which depends on load Cx and the Cs capacitor, must

not be so long that burst of the last device in the chain overlaps the burst of the first device. Should this occur,

the first and last devices may interfere with each other if the electrodes and wiring are adjacent to each other.

One simple solution to this problem is to physically separate the traces and electrodes from devices that have

overlapping bursts.

DIP Package: DIP devices are marked 'QT115'

SO8 Package: Marked 'QT1' and also laserscribed '5'