On 17 April 2012 22:30, David Duffy (AVD) wrote: > A quick look online for commercial sensors only seemed to reveal ones > designed for clean rooms (BIG $$), or actual smoke alarms. =A0Has anyone > been down this path before? > David... IIRC a smoke alarm I pulled apart (same principle but at an angle more like 45 deg) was constructed with a standard phototransistor and LED. The principle is sound but the issue is one of sensitivity. The reflectivity of smog particles is likely to be a lot lower than that of smoke from a nearby fire (lower concentration and probably lower particle size). Constructing the plastic holder could be done by folding sheet metal or rapid prototyping. Best regards, Brendan --=20 Brendan Gillatt http://www.brendangillatt.co.uk --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .