ORP12 etc Cd-S LDR and the RoHS directive.

Why do you care? Audio companders or something like that? I do a lot of analogue stuff, but haven't used a CdS cell since probably 1978.

Cheers

Phil Hobbs

They are still very widely used as daylight sensors in PIR sensors and lighting photocells. I saw some recently in a CE marked, UK produced sensor where the CdS LDRs had been 'trimmed' in production by scraping off some black paint covering the active area. We use 'light to digital' sensors in our higher end sensors.

JB

When contractors installed fire alarms and emergency lighting in the flats, I rescued a few light fittings from the outdoor utility lighting that had daylight shut off.

A couple had mains voltage LDRs driving a hotwire/bimetal relay, a couple more had silicon photodiodes - near as I could tell; similar to BPW34. The photodiode drives an op-amp buffer/comparator - its a proven circuit for sensing daylight with a silicon photodiode, but an LDR still wins hands down for spot on daylight response.

You never know - I might want to submit a magazine project that uses them, that might get a bit tricky if the supply dries up and they start changing hands at collectibles prices.

They're complete crap if you actually want to measure anything, though--their resistance can vary as much as 5:1 based only on previous history.

A far better way to make a wide-range photometer is to measure the open circuit voltage of a photodiode, and temperature-compensate the result.

Cheers

Phil Hobbs

They're perfect for those plastic frogs that emit a novelty sound effect when anyone walks past and casts a shadow on the sensor.