we've looked for a beam breaker sensor - sounds easy, but all we've found have been expensive and/or far from compact / simple to install ...
this seems to offer a slightly different approach that avoids such issues - it comes in two versions :
http://www.oomlout.co.uk/infra-red-d...ble-p-229.html
http://www.coolcomponents.co.uk/cata...GP2Y0A21YK.pdf
the A-type gives a signal that hopefully could be used with an QAI module & a suitable trigger setting, and the D-type that hopefully could be used with a digital input on any of many modules ...
either way, it would be positioned as a beam-breaker - ie: looking across the direction of passage ...
hopefully, because the inputs & outputs are not quite ideal - ie: one or two extra components might be required to power it off IDRAnet and make it compatible with module interfaces
any thoughts, might it work ??