RC Decay

The figure below shows a Resistor-Capacitor (RC) Decay circuit that conditions a capacitive sensor. The time it takes for the voltage to decay to a threshold is a function of the capacitance, CSEN. A PIC® MCU produces a single-pole step response (voltage) with an RC decay. This circuit measures the decay time where the threshold is proportional to VDD. R1 has a low-temperature coefficient to minimize temperature errors. The PIC MCU provides the switching and control needed.



  • Ratiometric correction of VDD and temperature
  • High accuracy
  • Simple timing measurement


  • PIC MCU resolution limitation
  • Digital noise
  • Threshold needs to be ratiometric

Sensor Examples:

  • Capacitive humidity sensor
  • Capacitive touch sensor
  • Capacitive tank level sensor
© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.