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Topic: Fotodiode or IR LED? (Read 1 time) previous topic - next topic

RustyRyuu

HI

I´ve a problem identifying a piece of hardware. I made many tests for trying to undo the mess but I only messed more my mind.

The problem is that I don´t know if its an IR LED or an Photodiode.
It is DIP encapsulated, transparent, with two legs.
It doesn´t seem to work properly. I´ll tell you my test results:

- Multimeter testing. Diode mode:
     + Directly polarized: Didn´t light on. Multimeter measured 0.148
     + Inverse polarized: Didn´t light on. Multimeter measured 0.148

- Polarizing at 5V with 1kOhm resistor. Multimeter at 20V range:
     + Directly polarized: Didn´t light on. Multimeter measured 0.28
     + Inverse polarized: Didn´t light on. Multimeter measured 0.34
Covering from light or exposing to it DIDN´T make difference.

- Polarizing at 5V with 270Ohm resistor. Multimeter at 20V range:
     + Directly polarized: Didn´t light on. Multimeter measured 0.40
     + Inversey polarized: Didn´t light on. Multimeter measured 0.59
Covering from light or exposing to it DIDN´T make difference.

So, with that results it doesn´t seem to work like an IR LED either a photodiode. What is it?
Do you think it broke down???? Could be another thing?. I mean, it was supossed to be IR stuff, but could it be some kind of hight intensity LED which I need high voltaje or current to light on??. I don´t know what to think...

Thanks for your time and patience
 

123Splat

A picture might help.
Explain directly polarized and inversy (?) polarized. so we are all on the same page.
You did not say if light exposure made any difference during the diode mode test.

5V @270 Ohm is about 18mA.  some LED's take about 20mA to light up.  If it is/was IR, how do you propose to know if it light up?

MarkT

What forward voltage do you get at room temperature with 1 -- 10mA or so forward current?

Silicon photodetectors (0.7V) will be a lot less than a IR LED (1.1V), IIRC.

Photo emitters are not silicon, but a direct-bandgap semiconductor (normally).  Of course
a photodiode doesn't have to be silicon, but many are.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

Grumpy_Mike

Quote
Didn´t light on.
How are you determining this?
You will not be able to see the light from an IR emitter. You may be able to see it through a camera viewfinder but only dim.
What you really want is a camera without any IR filter. The NOIR Raspberry Pi is one such camera.

The voltage required to light an IR emitter is in the order of 0.7 to 1.4V so you don't need a higher one.

Quote
Covering from light or exposing to it DIDN´T make difference.
It wont, if it is a detector there will be an IR filter built in to stop that happening.

RustyRyuu

A picture might help.




Explain directly polarized and inversy (?) polarized. so we are all on the same page.
Directly polarized is, as in every electronic component: anode connected to positive of the power supply and cathode connected to the negative. Inverse polarized is the opposite. Perhaps I didn´t choose the correct expression because I´m not english.
A diode, either IR or Visible Light must not let pass any current if inverse polarized, and must have a 1.3 - 2-5 voltage drop if directly polarized.



You did not say if light exposure made any difference during the diode mode test.
You are right, I forgot. I just tested and there are no differences

5V @270 Ohm is about 18mA.  some LED's take about 20mA to light up. 
Right again. I tested with 3V3 at 0.20 mA. Multimeter measures 0,46 directly polarized, 0,60 inverse polarized. Still not light on.

If it is/was IR, how do you propose to know if it light up?
How are you determining this?
You will not be able to see the light from an IR emitter. You may be able to see it through a camera viewfinder but only dim.
What you really want is a camera without any IR filter. The NOIR Raspberry Pi is one such camera.
I use my mobile camera. It sees perfectly all the other IE LEDs I have, including a KY-005 module that has a LED that seems equal that the one I can´t identify, and all my IR remotes, including Arduino ones and TV one. The camera shows me the IR LEDs with a well differenced purple-pink light.

The voltage required to light an IR emitter is in the order of 0.7 to 1.4V so you don't need a higher one.
Tried again, with 1V5. Nothing

It wont, if it is a detector there will be an IR filter built in to stop that happening.
I´m not sure, but I think that that type of photodiode hasn´t any filter. Is a simple photodiode, not a phototransistor like V1838. (if it is a photodiode, of course). So natural light might affect it because natural light has IR waves too.


What forward voltage do you get at room temperature with 1 -- 10mA or so forward current?
5V with 1kOhm resistor gives us 5mA. So, second case:
- Polarizing at 5V with 1kOhm resistor. Multimeter at 20V range:
     + Directly polarized: Didn´t light on. Multimeter measured 0.28
     + Inverse polarized: Didn´t light on. Multimeter measured 0.34
Covering from light or exposing to it DIDN´T make difference.

Silicon photodetectors (0.7V) will be a lot less than a IR LED (1.1V), IIRC.

Photo emitters are not silicon, but a direct-bandgap semiconductor (normally).  Of course
a photodiode doesn't have to be silicon, but many are.
I don´t understand what do you mean


Grumpy_Mike

That photo look like an emitter not a detector. I would expect a filter in a receiver and I do not see one.
 
Quote
Tried again, with 1V5. Nothing
No that is not what I suggested. I said as the forward voltage drop could only be 1.5V you did not need to try anything higher than the 5V you were using to drive the LED.

 
Quote
It sees perfectly all the other IE LEDs I have,
Do you know there are two main wavelengths of IR diodes? Your camera might not be able to see both.

However my conclusion is that you are not doing the test correctly or your LED is broken.

123Splat

Photo looks like a LED (Emitter, if IR), dished cathode also serves as reflector.
If IR, needs at least 2.2V minimum.
Note that an LED can also be used as a detector (most inefficiently) for it's intended wavelength.

MarkT




Directly polarized is, as in every electronic component: anode connected to positive of the power supply and cathode connected to the negative. Inverse polarized is the opposite. Perhaps I didn´t choose the correct expression because I´m not english.
A diode, either IR or Visible Light must not let pass any current if inverse polarized, and must have a 1.3 - 2-5 voltage drop if directly polarized.

Ah, that's polarity.  Polarization is something else in English (several other meanings in fact).
Quote
I don´t understand what do you mean
Silicon is an indirect bandgap semiconductor, which means it is very inefficient as a light emitter.
Direct bandgap semiconductors like GaAs are far better for emitting
light from a pn junction.  Either kind can detect light though, but silicon needs to be thicker.
https://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps  Different semiconductor materials have different bandgaps
and thus different forward voltages.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

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