Novel surface mount LED ammonia sensors

Low-cost colorimetric ammonia gas sensors have been developed using a pair of surface mount light emitting diodes (LEDs), ammonia specific chemochromic reagent and a simple PIC microcontroller circuit. The key feature of this sensor is the use of an LED, rather than a photodiode, for light detection. The use of surface mount diodes means a significant reduction in the final size of the sensor, and the amount of reagent coating required. The cost of the drive circuitry is also kept to a minimum by avoiding the need for an A/D converter. Results have shown that this low-cost device can be used for the detection of ammonia vapours in the lowppm range. This configuration is applicable to a wide range of colorimetric based gas sensing aterials.