Suraj143

There are two items that I’m confusing.
They are PHOTO DIODE & the PHOTO TRANSISTOR.

The wikipedia doesn’t tell about the medium they travel.

What I want to know is PHOTO DIODE/TRANSISTOR does it sending & receiving IR beams or some other medium like light etc.

Please explain this very simply.

Thanks

dknguyen

Both receive light. One is built more like a diode and one is more like a transistor. The phototransistor one is more sensitive but a photodiode is faster.

What do you mean by"medium they travel"? If you mean wavelength/frequency of light/electromagnetic radiation that they detect then it depends on what materials were used to make them.

Suraj143

Thanks dknguyen for your response.

If I buy a photo transistor (I don’t know the number) then to work it out what I need?

I mean if I focused a LED in front o the BASE will it turn on the transistor?

Or do I need an IR light in front of the BASE?

dknguyen

Yes. Shining a light on a phototransistor is like applying current to the gate of a bipolar transistor. THey work the same way. I don't know what kind of light you need- it depends on the transistor you buy.

Suraj143

Earlier I thought a photo transistor needs an IR beam to work out.

Is there any special LED’S made for this purpose. I mean to focus the light beam directly to the base of the transistor. Or many people using standard LED’s?

dknguyen

Phototransistors can have lenses in them to focus light. Special LEDs can also have lenses to focus the light too. You can use standard LEDs if you choose a phototransistor that works with standard light.

Torben

Infrared is light, it's just not visible light.

Around here, the electronics shops often sell a matched pair with one IR LED and an IR phototransistor. The IR phototransistor can trigger from visible red light, but it responds best to light in the near-infrared (i.e. just a bit too low of a wavelength to see).

Without knowing what exactly you are trying to do (i.e. what the project is) then I can't help you pick a light source.

The phototransistor doesn't care about modulation or anything. You would have to add circuitry to detect the modulation. Same with the diode: it will not modulate its output by itself without additional circuitry to do so.


Hope this helps!

Torben

Suraj143

Can I call photo transistors as IR photo transistors?Because they use IR.

Then what about the IR bulb can I call that also as a photo diode?

I'm trying to do is the sender sending a signal all the time to the reciever.when the beam is broken its activating a relay thats it.
I did with a LDR & a laser but now I want to do with another type sensors.

ericgibbs

hi Suraj,

There's lots of data on Google.

Examples:
http://sales.hamamatsu.com/assets/ht...iode/index.htm

http://optoelectronics.perkinelmer.c...cteristics.pdf

http://encyclobeamia.solarbotics.net...ransistor.html

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Torben

You can call *some* phototransistors IR, but only if they respond best in the IR portion of the spectrum. Other phototransistors may respond to other wavelengths. Check the packaging and the datasheet.

I would say yes, in the strict sense of the term; it emits light, ergo it is a photodiode. However, the term "photodiode" usually refers to a detector diode, not an IR transmitter. Calling it an IR photodiode would probably confuse the issue. Call it an IR LED instead.

Google for "beam break detector", and search for those words on this forum. There is lots of information on the topic.


Torben