Is a CdS photoresistor a good detector for green light?

[Phil]

If you're adding a secondary LED, use an ultrabright green or yellow one. Of course, if going this route, you could just use a cheap optocoupler.

I like CdS photoresistors, though - their ubiquity dealt the much-loathed ROHS regulations a crippling blow when legislators discovered that they couldn't ban cadmium from everything.

Phil M1GWZ


On 4 Sep 2013, at 01:31, Rob Seastrom wrote:

> 
> Hey folks,
> 
> I'm on the cusp of throwing together something quick and dirty (and
> raspberry pi based probably; the price is right) that will talk to a
> couple of sensors hanging over the "cycle complete" LEDs on our washer
> and dryer and send appropriate text messages to a cell phone when
> they're done.
> 
> I was thinking about a CdS photoresistor (they're making 'em *tiny*
> these days!) with one leg hooked to Vcc, the other to a pull down
> resistor to ground, with the connection between the two hooked to a
> binary input pin of the Pi.  Kind of a quick and dirty "light
> controlled voltage divider".  Should work for a high impedence pin on
> the Pi with minimal fuss.
> 
> Tape the whole affair over the LED (maybe with a software controlled
> LED stuck to the back so that it can be lit to not lose having an LED
> on the front of the device when the cycle is done).
> 
> Only thing is, I'm not sure what the sensitivity of a typical CdS
> photoresistor is in the green band, and LEDs aren't very broadband so
> I can't get by on slop if this is a blind area for them.  Spec sheets?
> Ha.  That's like trying to find a datasheet on a 2.2k gold band
> resistor.  These things are buck-apiece commodities.
> 
> Can anyone shed some light (pun intended) on the receive passband of a
> typical CdS photoresistor?
> 
> Thanks,
> 
> -r
> 
> 
> _______________________________________________
> Tacos mailing list
> Tacos at amrad.org
> https://amrad.org/mailman/listinfo/tacos