Abstract:

A low-cost chemical sensor comprising surface mount light emitting diodes (LEDs) has been developed for colorimetric based gas detection. The device consists of a pair of LEDs connected to a simple PIC microcontroller circuit, and in most basic form requires the use of only 2 I/O pins on the chip. The key features of this sensor are the use of an LED, rather than a phtodiode for light detection and an all-digital light detection protocol that leads to a reduction in cost and power consumption by avoiding the need for an Analog-to-Digital converter (ADC). The surface mount diodes employed are more compact than standard LEDs, and are more amenable to coating by solid-state sensor films. Results are presented from sensors employing a chemochromic ammonia sensitive film and demonstrate detection of this target in the ppm range. The configuration is applicable to a wide range of colorimetric based gas sensing materials.