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Buy an IR switch

  1. Dec 16, 2009 #1
    Hi all out there. I had recently salvaged an IR bulb from a TV remote (universal). The component I am in search for is an IR switch, that is, completes a circuit only when a signal from an IR LED is received. Could this also otherwise be made with common household stuff?

    I know that I may get many queries on specifications after this, so I am posting the right here. It is not something signal specific that I am searching for, but I want a receiver able to receive the signals of all, or at least of an universal remote.

    Besides, take this as a general knowledge question. IR stands for infrared, and that stands for heat. If I were to click a remote, at least repeatedly, why don't I feel any warmth?

    My father says that the heat transmitted is very small, and that should mean that our body may well be above the temperature the LED emits. Here it is the main point: why don't we trigger off the IR receiver in our television ourselves, by our body heat, or for the same purpose, an electric heater, or so on?

    And a final question: what do you mean by frequencies in infrared? Any fluctuations in temperature or wavelength? If the wavelength were to change, wouldn't it go towards the spectrum of visible light or move towards radio waves?
  2. jcsd
  3. Dec 17, 2009 #2
    Infrared covers a wide range of wavelengths from the heat that you can feel to wavelengths that are slightly longer than red light which you can't. The wavelengths in the remotes are the latter.

    The "bulb" you salvaged is really a diode (LED) that shines with infrared light when current passes through it. The remotes don't just turn on the LED, they pulse it with a code, a different code for each function. Different manufacturers use different codes. A universal remote contains the codes for most of the manufacturers. This is why you have to enter in a number corresponding to the particular model of television you have.

    There are IR sensors, some with very high gain amplifiers, that can pick up a remote from a long distance or in very bright ambient light. These are not switches however. The signal they receive must be decoded and then the function for the corresponding code is activated. This is done by a micro-controller in the television.

    Usually the frequency referred to when talking about IR is the modulating frequency or pulse rate of the code.
  4. Dec 19, 2009 #3
    So in a way, you mean to differentiate the heat emitted from our bodies, from infrared wavelengths closer to the visible spectrum.

    By the way, I did find out part of what I have been searching for. A IR phototransistor. By the way, I didn't tell you what I intend to do. In a way, I plan to make a wireless telephone communication using two loudspeakers from toys, like we could make a wired connection by connecting two loudspeakers, but this time, I plan to use IR LEDs for the transmitter end, which will emit IR waves when something is spoken into the speaker, hence causing current to pass through the LED and make it emit infrared rays in accord with the electric fluctuations caused by the speaker.

    As for the receiver end, the phototransistor will pick the signals of the IR LED and will reproduce speech in the amplifier.

    Now, I do have a few questions:
    • Could you attach me a schematic diagram of making a switch with an IR phototransistor?
    • How do I make the receiver end of the telephone?
    • How do I amplify the IR waves of the transmitter end of the telephone?
    • If I were to make a RC car with motors controlling forward and backward movement, how do I activate only one set of motors at a time? Using IR LEDs of different frequencies, then how do I make sure it activates only one set of motors by activating only one phototransistor, either going forward or backward?

    Last edited: Dec 19, 2009
  5. Jan 10, 2010 #4
    I could be completely wrong because I dont know too much about the hardware aspect but I dont think it would work the way you think. If you're talking into a microphone and as you're talking activating the LED, it wont really be blinking the way you think it will be.

    Someone correct me if Im wrong but as soon as you start talking into the microphone it would turn the LED on and wouldnt turn off until there is no sound being inputted. If this is how it would actually work, which honestly Im not sure, there would be no way to decode the message sent to speech on the other end because all that would be recived is a solid light.

    If Im wrong please someone correct me because I would like to know if Im right :)
  6. Jan 10, 2010 #5
    Correct. Near infrared, i.e. wavelengths around 700-1000 nm, would require very hot objects to emit via blackbody emission (i.e. light emitted due to temperature). Of course the sun does emit in these wavelengths, so you'll need to take that into account for using your device around any sunlight. To answer one of your earlier questions about not feeling heat from an IR LED - the amount of energy coming from the LED is very small. If it were emitting very high energy you would be able to feel it, but then again the same would apply to a visible LED.

    I think what is trying to be done is similar to these, except with a near IR LED.


    One problem I see with the proposed system, which I believe gotem3303 is alluding to, is that the signal from a speaker is analog whereas what you're talking about is binary - e.g. a photodetector transistor's output is either high or low depending on if incident light is above or below a threshold. You might be able to get by with a photodiode, maybe an Indium-Gallium-Arsenide (InGaS, often pronounced "in-gas") type. I would also be concerned with the signal traveling any sort of distance. I've used red LED devices that transmit/receive sound and they need to be quite close (and in a dark room) together to minimize noise (laser devices can be quite a ways apart though).
  7. Jan 11, 2010 #6
    You can go to this website: "[URL [Broken]
    [/URL] , there are many about inventions of the knowledge.
    Last edited by a moderator: May 4, 2017
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