Guard channel in Qtouch Acquisition Method allows one key to be configured as a guard channel to help prevent false detection. Guard channel keys should be more sensitive than the other keys (physically bigger or larger Cs).To enable key as guard channel, the designated key is connected to a sensor pad which detects the presence of touch and overrides any output from the other keys using the AKS feature.
The key can be configured to have a guard channel function by adjusting a number of independent settings. The Guard channel is designed so that it is likely to be activated unless a key is accurately touched.
The guard channel sensor must be set up so that it is slightly more sensitive than the keys that it surrounds. The exact amount of increase depends on the application and is best determined by experimentation.
There are three methods of increasing the sensor sensitivity that can be used in combination:
- 1.
Increasing the size of the sensor.
- 2.
Increasing the value of the Sample Capacitor (Cs).
- 3.
Adjust the detection threshold for the sensor.
The sensor size and capacitor values should be altered to establish the base sensitivity for the sensor. Once these values have been established, the detection threshold can be used to fine tune the sensor.
The figure in Figure 1 illustrates how a Guard sensor/key is to be visualized.It has six keys and five keys are surrounded by a Guard Channel.
Refer QTAN0031 for further information on Guard Channel. http://www.atmel.com/dyn/resources/prod_documents/QTAN0031(2).pdf