Metal-oxide semiconductor gas sensors offer valuable advantages, such as high sensitivity, low cost and small dimensions. However, it is well-known that significant problems, such as cross selectivity and lack of long term stability, still affect their performance. Several studies point out that the modulation of the sensor temperature may improve the sensor performance, and different thermal modulation methods are currently available. In this work a temperature modulation scheme that needs no a priori information about the sample under test is presented. According to this method the sensor temperature value is set, through the sensor resistance value, via an Astable Multi-vibrator Circuit (AMC). The resulting output signal forms a cyclic pattern of pulses. Pulses shape depends on the sensor resistance while the pulse length depends on the measured gas. The method is here illustrated through a three-class …