LDR Component

[mabuyu]

Where can i find the LDR Component ( Light Dependent Resistor ) in Multisim ?

i searched and only found LED !

So, Can someone help me finding that ?

[kittmaster]

the closest thing I found was in master database > sch_cap_syms > photo transistor

I don't think there is one in the master database and you'll have to make your own part.

[mabuyu]

When i use the component you said in your reply, i got an error: "unknown device type" !!

And, How can i create my own part ? is there's a tutorial for that ?

[kittmaster]

http://zone.ni.com/devzone/cda/tut/p/id/3173

[RnDMonkey]

I wonder if this is even possible? If it is not coded in right now, you'd probably have to find a SPICE model somewhere online or write one from scratch. Depending on what you intend to use it for, you might just be better off going with Kittmaster's idea and using a phototransistor. If you really need something that works like a potentiometer, you might not be able to do that without quite a bit of extra circuitry.

[lacy]

That is what I do when simulating LDR type componets. I just use the potentiometer as a substitute because basically that is all a LDR is. When light shines on  it the resistance changes either up or down and this is detected by a circuit to perform some function when a certain threshold is reached.

[mabuyu]

i tried to use the potentiometer instead of LDR, But i got the following Error:
"Error in line 170 on rx1 3 x1_open_2 2 0.000e+000"

And, The circuit i used in MULTISIM FORMAT is attached with this reply.


Message Edited by mabuyu on 06-08-2008 09:15 AM

[lacy]

I am going to post a circuit for you to examine. It is your circuit with a few modifications to possibly simulate your LDR. This is not going to be exact but a close approximation of how an LDR would work. I will give an explaination below. Feel free to modify it to suit your application or need.

Used an opto coupler to simulate a light source and receiver. I added a pot to the collector of the photo trasistor to simulate the varying nature of the actual LDR. The unfortunate part is that you have to manually adjust this pot whereas the LDR would do this automatically depending on the strength of the light source. This is a close as apporximation as I could come. Remember that the optocoupler  and pot is your light source and receiving resistor.

I would like to make a note here. I used the 4N38 because it seemed it was the only one that gave the correct results. The rest that I tried in this configuration gave me a negative voltage on the output and I have yet to figure out why. It is possibly a model problem, but I don't know yet

The circuit is below.

[lacy]

The way you have your circuit configured would not lend itself to trying to simulate with just a potentiometer. The only way that could be done is to completly eliminate the light producing side of things and use the pot on the output side and pretend that as you adjust the resistor the light is getting stronger.

The circuit in my last post is a little better, but it is not a true LDR in any sense of the word. I hope maybe you can make use of it.

[mabuyu]

Yes, i got you.

But, i need a true LDR to use in our world out of the simulation .. So, i think there's no way to simulate that !

Anyway, Can you provide me with a circuit ( Only Drawing ) for True LDR working in our world ?