Sensor Ganging to Optimize Power Consumption

Capacitive touch screens are slowly replacing mechanical buttons in electronic goods. A capacitive screen has numerous benefits over mechanical buttons. However, they are not easy to develop. For one, capacitive touch screens consume a lot of power. So the challenge in embedded development is to balance power consumption with ease of use. In this context, a technique called sensor ganging is showing lots of promise.

Before we go there, we must understand a concept called ‘active time’. Active time is basically the duration where the capacitive sensor is working. It includes scan time, data processing (by sensors) and post-sensing scan activities. When there is no work, the sensor goes into ‘sleep mode’.  So the active-sleep time works like a cycle.

What if you could combine all the sensors and scan all of them together, like a single sensor? The capacitive sensor algorithm can consider all the ganged sensors as one sensor. This technique reduces the capacitive sensor’s active time. Consequently, power consumption by the sensor is also reduced.

Embedded developers should know the four steps in sensor ganging. First is, selecting sensors to gang. Second, understanding that there might be parasitic capacitance between the sensors (if this is found true, the sensors might have to be re-ganged). Third is, making component settings for the ganged sensor and finally, implementing the firmware. Sensor ganging is a relatively new field but it has a lot of promise.