Interface electronics for resistive and piezoelectric polymer gas sensors

An electronic interface has been designed and built which allows changes in the properties of hybrid conducting polymer sensors to be measured by a host computer. It has analogue circuitry which is used to measure polymer resistance, and digital circuitry which provides a measure of the period of oscillation of piezoelectric element (PZE) with a polymer deposit. Initial tests were made with physically separate sensor types but the design is intended for a hybrid sensor with a single polymer deposit on a PZE. A Field Programmable Gate Array (FPGA) has been configured to act as a period meter, which achieves a resolution of better than 1 part in 2 million. An embedded single-chip microcontroller accepts simple commands from a host computer and coordinates the activity of analogue multiplexers, a precision ADC, and the FPGA to give 1 reading per second from and array of 6 hybrid sensors. Other features have been included which allow for temperature measurement and control, numerical pre-processing as well as programmable gain and offset. The result is a superior instrument which aims to meet the emerging needs of industrial and research applications.