Water pollution assessment by microcontroller-based lock-in amplifier

This paper presents a new approach to the classical design and implementation of a Lock-In Amplifier (LIA) applied to impedance measurement of interdigital capacitive sensors in order to evaluate water polution. It is based on a general-purpose microcontroller and an active band-pass filter. The design uses a wave generator (AD9833) as source for the reference signal and an Analog to Digital Converter (ADC) from the microcontroller to sample the device under test (DUT) signal. In the particular context of this study, the sensor responses are evaluated by conductance, impedance and capacitance measurements on water-chlorine and water-salt solutions.