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How To Let Capacitive Sensors Replace Mechanical Switches

Aug 03, 2017

The Capacitive touch sensor interface is usually composed of a capacitive sensor, a capacitor digital converter (CDC), and a primary processor. The sensor is manufactured using a line (trace) or a flexible circuit on a standard two or four-layer PCB, so no external components or materials are required.

Reliable sensors must be unaffected by external environmental changes and can maintain accurate sensitivity levels under any working conditions. Changes in temperature or humidity can lead to changes in the characteristics of the PCB material, so the output level of the printed circuit capacitance sensor will drift. For example, this can happen when a user starts an air-conditioned car into a humid environment. To avoid intermittent contact errors, the CDC must include real-time drift compensation functions.

As environmental conditions change (e.g., temperature or humidity rises), the sensor's ambient parameters (measured by the CDC during the user's failure to contact the sensor) drift. In order to compensate, the high and low end threshold power needs to be changed dynamically to determine effective sensor contact. The reference level at position 2, 3, 5, 6 is readjusted to maintain the optimal threshold reference level, thereby automatically tracking and compensating drift errors.