I'd like to put together some oxygen and ammonia sensors for a chicken house.  I want to read the sensors with a PIC and control some equipment as a result of the reading.  I think I'd be dealing with parts per million in the air.  Does anyone know where I can get the sensors?  Or for that matter, does anyone know if there are some already-built ones out on the market with communication and control functions?

Carl Connett
dayspring.com