Mod LDR specs with parallel resistance?

[Luke51411]

Typically you are looking for certain specs of an LDR for applications that use opto devices. I was just wondering if anyone has had any success modding the resistance response of an LDR by using either parallel or series resistance or a combination to get it to act closer to different specs than it was manufactured for. For instance if you need an LDR with an off resistance of 10k but you only have units with off resistance of 1k it seems like it would be simple to add a series resistor to get that part of the circuit to a minimum resistance of 10k. Also it seems like you could add parallel resistance to lower the max resistance. I know that these methods would work I'm just wondering if anyone has achieved useful results with this practice.

[PRR]

You often use some kind of stopper/shunt to limit the extremes of an LDR.

But if you gimmick a way-wrong LDR with plenty of fixed resistance, the action is mostly "fixed", with a too-quick change in the middle.

Build it. Try it. Can't hurt much. Might learn some.

[armdnrdy]

For instance if you need an LDR with an off resistance of 10k but you only have units with off resistance of 1k it seems like it would be simple to add a series resistor to get that part of the circuit to a minimum resistance of 10k.

A LDR will be spec'd at 1K for a certain current. If you limit the current below what is spec'd for 1K, the on resistance will increase. This is usually accomplished with a trimmer in a circuit which uses an optocoupler.

Now I noticed that you referred to off resistance and minimum resistance in the same sentence.

You do realize that the off resistance is the max resistance when the LED is not lit or dim.
On resistance is when the LED is at it's brightest and resistance at it's least.

[Luke51411]

Yeah I knew that in practice, just got it mixed up trying to explain. Thanks.