Infrared receiver acting weird

[Lac]

I'm currently playing aound with some IR LEDs and recievers, but the reciever is acting weird. I'm using the simple scematic from this page but whenever i plug 5V into the circuit, the led lights up even if the IR LED isn't activated. It looks like the IR receiver is always letting current trough, even if it doesn't receive an IR signal at its base.

What can be wrong? Is there a possibility that the receiver is broken?

Cheers!
Lac.

 

[Exo]

did you try it in complete darkness?
this circuit will act on abient light also.

 

[Lac]

Sec, shall try it now.

Cheers.
Lac.

 

[Lac]

nope. still it acts weird, even in complete darkness.

Cheers!
Lac.

 

[Exo]

well, it's pretty basic, there can't be much wrong...

are you sure you're using the right transistor (NPN) and phototransistor?

 

[Nigel Goodwin]

well, it's pretty basic, there can't be much wrong...

are you sure you're using the right transistor (NPN) and phototransistor?

Is the light from the LED reaching the phototransistor?, if it does it will turn the phototransistor ON and stay on permanently.

It's a really crappy circuit though! - what are you trying to do with it?.

 

[Someone Electro]

Meaby adding an potencimeter to adust sensetiverty.

 

[Lac]

ohh... I just noticed that I have got a IR-Receiver, not a Phototransistor. I thought that IR-Diods used IR-Receivers, while Photo-Diods used Phototransistors, or am I wrong here? Whats the difeerence between photo and IR diods then? and what about the ir-receiver and the phototransistor?

Cheers!
Lac.

 

[Nigel Goodwin]

ohh... I just noticed that I have got a IR-Receiver, not a Phototransistor. I thought that IR-Diods used IR-Receivers, while Photo-Diods used Phototransistors, or am I wrong here? Whats the difeerence between photo and IR diods then? and what about the ir-receiver and the phototransistor?

An IR receiver is a complete IC, containing amplifiers, AGC, demodulators and modulation detection. They have three pins and look nothing like a photo-diode or phototransistor.

 

[Someone Electro]

How cod you mistaken an IR reciver(3 pins) whith an foto transistor(2 pins).

An photo diode shod work instaed of an photo transistor.

Here insted of an photo transistor an photo diode is used

On pic1 the rele coil stops geting power in the dark.On pic2 i its the poposite

Wait a minute...Ops The ground shod me 4.5 V and the 4,5 V the ground

 

[Someone Electro]

O and replace R1 or R4 whith potencimeters to have the sensetivety ajustable

 

[Exo]

ohh... I just noticed that I have got a IR-Receiver, not a Phototransistor. I thought that IR-Diods used IR-Receivers, while Photo-Diods used Phototransistors, or am I wrong here? Whats the difeerence between photo and IR diods then? and what about the ir-receiver and the phototransistor?

Cheers!
Lac.

what do you want to use this circuit for? Maybe there's a way to use the IR receiver to make a stabler circuit, wich doesn't act on ambient light.

 

[BartSimpson]

what do you want to use this circuit for? Maybe there's a way to use the IR receiver to make a stabler circuit, wich doesn't act on ambient light.

Ke ? Don't IR receivers usually require a carrier signal of some type ?
There are at least 4 or 5 common carriers that I am aware of.

Just to make thing interesting, each IR receiver usually can only detect one of them ...

Then there is the other little problem where each IR receiver is usually tuned to a specific IR wavelength. Granted while 980nm seems to be the mid-range and most can see a little either side of this, you've still got a large bandwith to try to cover if you don't know the frequency response of the receiver.

Since an IR photo-transistor costs about 15 cents, I would have though buying a real photo-transistor would be the cheapest way out.

Not saying it can't be done, but I'm kinda curious how you're going to do it without generating a carrier signal for the IR receiver.

- Edit to fixup dumb spelling mistakes. Gotta layoff of the red wine

 

[Exo]

That's why I asked what the application is. If he wants to use it with a remote control he already has (for a TV, video,...) then it'll work fine with the ir receiver...

Almost all remote controls use a 38 - 40Khz signal wich is what the receiver will repond to

 

[BartSimpson]

Cool, just checking

Except a lot use other "weird" frequencies, some as high as 56khz...
Not meaning to be difficult, but

 

[Nigel Goodwin]

Cool, just checking

Except a lot use other "weird" frequencies, some as high as 56khz...
Not meaning to be difficult, but

I've seen the 56KHz ones listed, but never seen one actually used in anything - I doubt 'a lot' applies :lol:

I would suspect well over 99% of IR receivers used are 38-40KHz versions. The Swedish TV manufacturer B&O used to use 100KHz modulation, which was why they were not originally supported by 'One For All' remote controls.

 

[Someone Electro]

To make the circuit work on an spesific freq. put an bandpas filter betven the two transistors