Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: silent069 on June 06, 2008, 10:42:16 PM

Title: photoresistor needed
Post by: silent069 on June 06, 2008, 10:42:16 PM

hi all, i live in canada so im unable to order from radioshack.com (i dont see us as a shipping option)  this only poses a limit to me from ordering the photoresistors. and after checking online, i really cant find any other sites that offer the resistors for sale. www.mrrobot.com has them  for about the same price, just wanted to check the validity of this site before i made an order. if anyone here has a few kicking around they wanna get rid of, maybe we can work out a deal on them or something.
thanks in advance, 

Title: Re: photoresistor needed
Post by: pomprocker on June 06, 2008, 11:41:10 PM

http://www.parallax.com/Store/Sensors/ColorLight/tabid/175/CategoryID/50/List/0/Level/a/ProductID/175/Default.aspx?SortField=ProductName%2cProductName (http://www.parallax.com/Store/Sensors/ColorLight/tabid/175/CategoryID/50/List/0/Level/a/ProductID/175/Default.aspx?SortField=ProductName%2cProductName)

Title: Re: photoresistor needed
Post by: Private Reid on June 07, 2008, 12:00:46 AM

ebay has them (worldwide post)

Title: Re: photoresistor needed
Post by: silent069 on June 07, 2008, 07:07:52 AM

thanks for the response guys, ill have some pics of my robot up in the next few weeks, ill have the chassis done b4 my parts get here.

Title: Re: photoresistor needed
Post by: Admin on June 07, 2008, 05:55:04 PM

mouser.com and digikey.com also have them, but I think they call them phototransistors or something like that . . .

Title: Re: photoresistor needed
Post by: bens on June 07, 2008, 06:16:12 PM

While similar in function, phototransistors are different from photoresistors.

- Ben

Title: Re: photoresistor needed
Post by: Admin on June 08, 2008, 11:47:20 AM

What really defines them is the spectrum of light they operate with, no?

Title: Re: photoresistor needed
Post by: bens on June 08, 2008, 03:41:47 PM

I believe the key difference is that a photoresistor is basically a resistor whose resistance is a function of the incident light, while a phototransistor is a transistor whose gain is controlled by the intensity of incident light.  You could duplicate a phototransistor by using a photoresistor and a normal transistor (at least according to the minimal research I've just done on this topic in the past two minutes).

Another key difference seems to be that photoresistors have a much lower response time than photodiodes and phototransistors (which can be orders of magnitude faster, according to wikipedia).  Apparently this means that you want to use phototransistors for high-speed applications like data links and picture scanning.  I think you want to use photoresistors for things like color detection as you can get better analog measurements than with phototransistors, which are more suited to on/off type results.

- Ben