Sensor Ganging--Optimize Power in a Capacitive Sensing System — Part II: Page 2 of 3

August 13, 2015 //By Shruti Hanumanthaiah and Subbarao Lanka
Sensor Ganging--Optimize Power in a Capacitive Sensing System — Part II
Shruti Hanumanthaiah and Subbarao Lanka continues to consider the challenges of sensor ganging and how to optimize power in a capacitive sensing system.
this slow scan mode.

Power consumption varies between these two modes. The scan modes can be switched between the two modes dynamically to optimize power consumption and response time. When the user does not touch buttons, (i.e., when the UI is idle) the capacitive sensing controller is put into slow scan mode thus optimizing the power. When the user has touched the buttons the mode is changed to quick scan mode to optimize response time. In this section of this article, we will see how much power can be optimized with ganged sensors when combined with this technique of switching between quick scan mode and slow scan mode.
 
Problems solved by a ganged sensor

Power consumption
Now let us take an example application and see how sensor ganging helps in power optimization. We will also use dynamic scan mode switching as discussed in the previous section to optimize both response time and power consumption. Here is the procedure for average power consumption calculation:

 
Power consumption with dynamic scan mode switching Consider a capacitive sensing user interface in a digital photo frame with six buttons, for example. Let us take quick scan mode refresh interval as 50ms and slow scan mode refresh interval as 125ms. Let us assume that the total sensor scan time for six buttons is 9ms.

 

In the above example, with a ganged sensor, power consumption is reduced by 32%.

System Response Time

When a ganged sensor is tuned for proximity sensing, the system can have a good response time. Let us see how. As explained in the previous section, instead of using a separate sensor for the proximity detection, all sensors can be ganged to form a large sensing area that can sense the proximity of a human hand. In an application where you have backlight LEDs for individual sensors, when the proximity sensor detects a human hand, the backlight LEDs can be turned

Design category: 

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