Lowdown on LDR's

[frooshontay]

Can someone give me the lowdown on LDR's? I'm relatively new to the pedal building game. I have a good understanding of the basic components (transistors, resistors, capacitors, etc), but I'm new to LDR's. I've been looking at building a Clari(not) and a Tremulus Lune, which both use LDR's.

I'm having trouble figuring out which ones to order. What properties should I be looking for? For example, Tayda has one on their website, but very little information on it's properties. The only information it really give is a frequency of 650 nm.

Does anyone know of a good place to buy these? I only see one available at Tayda, none at Mammoth or PPP. I think SmallBear has some, but I'm still not sure what I'm looking at.

Also, is their a difference between photoresistors, photocouplers, LDR's, photocells, etc?

[IvIark]

An LDR is just a variable resistor where the value is determined by how much light is seen at the sensor.  They will have a specified light and dark resistance which will tell you approximately what the expected value of the resistor will be at fully illuminated and totally dark conditions.

The dark value can obviously be affected if the sensor has access to any other ambient light, and the light resistance can be affected by the colour and brightness of the LED you use with it.  This is why it's always worth experimenting on a breadboard first, or socketing the positions on the board so you can audition different LEDs to try to get the response you want.

People will often wrap together the LED and LDR combination using electricians tape or heatshrink tubing so that they can be totally isolated from external light sources which makes things easier to test because you can leave the box open when testing.

In terms of which ones to order, if it isn't specified on the layout then it wasn't on the schematic either so it's probably a good idea to ask the question of someone who has build the pedal to see what they used.  I stocked up on them a while ago because I suspect they may be banned soon by the EU because they contain cadmium, but the common values that I bought are:

5k light - 500k dark
10k light - 1000k dark
30-50K light - 2-3M dark

[Dave]

I find the ones with the lowest light resistance to be most useful. Orp12's are the lowest i've found so far with a light resistance of ~400ohms but they are relatively expensive. If anyone knows any which go lower then please do share.
Thanks
Dave