I'm almost ready to throw my LDR's out

[mstechca]

For the last while, I have been using LDR's as my light detectors.

I was thinking of switching to photodiodes because I only want to detect two levels of light: no light, and bright light.

Is a photodiode equivalent to a broken diode when no light falls on it?

and can someone give me some part numbers of photodiodes, becuase I may want to buy some shortly.

 

[Nigel Goodwin]

For the last while, I have been using LDR's as my light detectors.

I was thinking of switching to photodiodes because I only want to detect two levels of light: no light, and bright light.

Why do you think they may be better?.

'No light' is a very definate statement! - how is that achieved?, or do you mean 'very low light' and 'bright light'?.

 

[mstechca]

that too.

I dont want to detect 50 light settings.

I want my circuit to read the light level as digitally as possible. u know digital right? I'm sure u understand now.

 

[bmcculla]

Photodiodes are just like mini solar cells. They are a bit more complicated to understand than LDRs. Photodiodes are used in 2 modes: a voltage mode and a current mode. The voltage mode is more sensitive but the current mode is linear and higher bandwidth.

In the current mode the photodiode is like a blocking diode with no light. When light shines on it it leaks a current that is proportional to the light shining on it.

 

[Nigel Goodwin]

that too.

I dont want to detect 50 light settings.

I want my circuit to read the light level as digitally as possible. u know digital right? I'm sure u understand now.

A photodiode is just like an LDR, it's not ON or OFF, it varies with the light level - by suitable design you can make either of them switch ON or OFF at a particular light level.

That's why I asked why you wanted to change?, the answer appears to be because you don't understand how a photodiode operates?.

 

[guzzimac]

If you can't find a suitable photodiode, make yourself a phototransistor. Get a general purpose transistor in a metal case. Take a junior hacksaw and cut the top off it. works a treat and has got me out of trouble on a couple of occasions. Also looks quite cool if you leave the lid attached by a small amount and have it hinged back!

Rob.

 

[mstechca]

I wanted to see which light detector works best, because I'm making a remote light detector.

The digital receiver works fine. Yes its a superregen, and by default, the output is a 1, because what I get is noise.

What I want to do is make it so that when the transmitter is NOT activated by a reasonable amount of light (enough light so that you can read a book), it blocks out the noise. It seems that an LDR does not do the job.

So I need some other component that can detect light, and the only other one I can think of is a photodiode and a solar cell. I dont want to use a solar cell because they are too expensive, and bulky.

 

[audioguru]

An LDR would do the job just fine. A photodiode or solar cell would be the same. Your problem with your LDRs is that you selected the wrong value of series resistor for them or loaded them down too much.

 

[Phasor]

I don't know much about superregen receivers, but the general idea I'm getting is that you need a comparator, with hysteresis for noise rejection. Of course, I might be getting totally the wrong idea - tell me if I am :?

This is an off-the-top-of-my-head idea for such a comparator.

 

[mstechca]

An LDR would do the job just fine. A photodiode or solar cell would be the same.

When I checked tpub.com/neets, (technical publishing) They show that a photodiode and an LDR work differently. LDR uses light to control resistance, and (help me on this...) I think a photodiode uses light to control diode's functionality.

 

[Nigel Goodwin]

An LDR would do the job just fine. A photodiode or solar cell would be the same.

When I checked tpub.com/neets, (technical publishing) They show that a photodiode and an LDR work differently. LDR uses light to control resistance, and (help me on this...) I think a photodiode uses light to control diode's functionality.

Yes, they work in different ways, but both are analogue components and very similar to use - but they need connecting differently!.

For your stated purpose either is just as good as the other.

 

[audioguru]

An LDR reduces its resistance when light activates it. A photodiode leaks more reverse current when light activates it. Therefore they both "conduct" when lighted.
Their current is very low and not suitable to control something directly, so an amplifier is usually used to give a required output at a certain light level.

If you want the light sensing circuit to "switch" digitally at a certain light level then it is going to need a high gain amplifier like what is inside a digital logic gate.