Creating a Light-Activated Switch with a Photodetector Circuit

[Nothing000]

How would one set up a circuit where a photodetector closes a switch in a circuit once it detects light?

 

[berkeman]

Depending on the photodector, you would probably bias it up and do a current-to-voltage converter circuit. Then take that output voltage and amplify it a bit to get enough power to close your switch (like a relay?).

 

[Nothing000]

Hey berkeman. How are you? I am only in my second week of my first circuits course, so could you explain what you just said in slightly more detail.

 

[Nothing000]

I would probably want to use a PhotoConductor, huh?

 

[Gokul43201]

I would probably want to use a PhotoConductor, huh?

A photodiode is what you want to use.

Is this coursework?

 

[Nothing000]

No, just curious.

 

[Nothing000]

A photodiode you say? So let me know if I am correct. A photodiode detects when photons are entering it. When it detects enough photons it starts doing its job. Am I right so far?
The job that it does is it allows current to flow in the circuit (but only in one direction).
Is that right?

 

[Nothing000]

If I am right then wouldn't the photodiode act just like a switch only it "opens/closes" by the detection of light?

 

[berkeman]

Hey berkeman. How are you? I am only in my second week of my first circuits course, so could you explain what you just said in slightly more detail.

Hi 000, I forget if I recommended this book to you already, but "The Art of Electronics" by Horowitz and Hill is a good book to get to augment your early studies. It explains all about photodiodes and current-to-voltage conversion using opamps. Here's wikipedia's entry on photodiodes:

http://en.wikipedia.org/wiki/Photodiode

 

[Nothing000]

Thanks berkeman. I will pick up that book. And I read wikipedia's entry on photodiodes. I have extracted from that article that a photodiode would act just like a switch. The switch is open when no light is detected, and it closes when it detects light. Am I right?
Because that's what I want to do. I want to close a circuit when it detects light, and open it when it is dark.

 

[berkeman]

Thanks berkeman. I will pick up that book. And I read wikipedia's entry on photodiodes. I have extracted from that article that a photodiode would act just like a switch. The switch is open when no light is detected, and it closes when it detects light. Am I right?
Because that's what I want to do. I want to close a circuit when it detects light, and open it when it is dark.

No. When light hits a photodiode, a reverse photocurrent is generated. This photocurrent is small, so you need amplification to do anything with it.

 

[Nothing000]

Depending on the photodector, you would probably bias it up and do a current-to-voltage converter circuit. Then take that output voltage and amplify it a bit to get enough power to close your switch (like a relay?).

So would this apply to a photodiode as the photodetector?

 

[Averagesupernova]

Nothing: Check into a phototransistor. It behaves more like what you originally assumed. If I remember correctly, the ones I have used are 2 leaded devices.

 

[dlgoff]

I don't want to get ahead of your learning curve but http://home.cogeco.ca/~rpaisley4/PhotoDetectors.html" gives some circuits using various detectors as suggested by Beckeman and Averagesupernova.

Regards

 

[Nothing000]

Kick butt. Thanks dlgoff.