[IEEE TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers - San Francisco, CA, USA (24-27 June 1991)] TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers - A cheap interface for a general sensor, resulting in high selectivity and linear output signals: application to a two dimensional array of tin oxide gas sensors to detect carbon monoxide and methane