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Tv ir receiver

Discussion in 'General Electronics Discussion' started by Mustwin351, Apr 26, 2013.

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  1. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Does the ir photo transistor in a tv pass much current through it? Or does it simply receive the signal from the remote control and pass on that data to control the other electronics where a signicant amount of current flows?

    The reason I ask is I was wondering if it was possible to take it out and solder long leads on it to place it say a foot away from its original location?
     
  2. davenn

    davenn Moderator

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    that shouldnt be a problem. they usually have 3 connections ... +5V, 0V and signal (data)

    Note you may need additional IR shielding once removed from behind the IR small screen on the front of the TV

    Dave
     
  3. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Thanks Dave. Let me pose one more question.

    Say I have two identical TV sets. Could I take both IR transistors out and use just one and solder the leads in paralell to just one of the ir transistors. There by controlling both TV sets with one IR transistor.

    I'm actually not using TV sets but two pwm devices to light up led strips. Unfortunately have no schematic but I imagine the ir transistor works on the same principal.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The type of device Dave is talking about is an IR receiver module, which includes the photodiode, carrier filter, and demodulator, and produces a digital signal that pulls low when carrier is received. These modules are made by many companies and are universally used in TV sets and other products that use IR remote control. But they are not photodiodes. They have three terminals, as explained by Dave.

    If you have two circuit boards and you want to use a single receiver module, you need to make sure that the 0V rails of the two boards are commoned. If they are powered directly from a low-voltage DC supply, this is probably the case. If they are also identical, there should be no problem.

    (In the case of TV sets, the chassis may be half live, and in that case it would not be safe to bring wires out externally, nor to connect two sets together.)

    You should make several checks first, on an unmodified receiver board:
    (a) check that the IR receiver module has three pins;
    (b) check that one of the pins is connected (has continuity) to the 0V rail of the board's circuitry, and to the negative power supply input, if it's supplied from an external DC source;
    (c) check that the other two pins have positive voltage on them, relative to the first pin;
    (d) find out which pin is the data output - it's the one whose voltage drops when it's receiving data from the IR remote control transmitter.
    (e) the other pin of the IR receiver module will be its positive supply input. This pin is supplied by the receiver board.

    Connect as follows.

    0V rail of first receiver board, to 0V rail of second receiver board, and to 0V pin of IR receiver module.

    Ppositive supply rail of first receiver board to positive supply pin of IR receiver module (power the IR receiver module from one board; don't link the power rails of the two boards together).

    Data signal from IR receiver to the data signal connections of both receiver boards.

    This is the general way to do it. Without actually being there and having a good look at the boards I cannot guarantee that this is safe and will work. "Your mileage may vary".
     
    Last edited: Apr 26, 2013
  5. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Sounds good kris I will check that out and try it. Thanks!
     
  6. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Kris. I wired up the two boards as instructed and no pop or smoke! It works as I wanted 99% of the time. It is really strange though every once in a while somehow only one board receives the signal from the remote.... I have two led strips with one connected to one board and one to the other board. So every once in a while one will light up and the other one will turn off when I use the remote. The same problem as before but now I only have one IR receiver for both boards instead of two!!! How in the world is this possible?! It's crazy to me.

    Also I left the IR module on one board and for testing purposes used some jumper wires to make the connections to the board with the IR module removed. It is receiving a positive supply from only one board.

    Interesting to note I have a fade to off feature on the remote. The board with the jumper wires and no IR module dims to off slightly slower. I guess the wire's resistance is throwing off the resistive capacitive relationship. I don't know but the wires are only like 6".
     
    Last edited: Apr 27, 2013
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The demodulated remote control signal coming from the receiver is decoded separately by firmware in each board, which makes separate decisions about what the command represents and whether it is valid. Sometimes the firmware is not well written and it can misinterpret incoming commands depending on how they are timed in relation to the firmware's internal timebase. This is a possible explanation for your problem.

    If you simply want both LEDs to do exactly the same thing, it might be possible to drive the LED driver circuits on both boards from the output(s) of the microcontroller on one board. This may be a more complicated modification than using a single IR receiver for both boards. We would need to find out a lot more about how the boards work internally.

    Can you post the manufacturer and model number of the boards?
    Do you have a schematic diagram or a service manual for them?
    Can you post a photo of the component side of the board?
     
  8. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Ok I have a photo of the board posted on the flickr photo sharing site. http://m.flickr.com/?loggedout=1#/photos/[email protected]/8686340611/
    or try
    Www.flickr.com my profile name is [email protected] yahoo.com and search people unfortunately my computers down so I couldn't post it in the forum as I'm using an iPhone.

    As far as a schematic I do not have one. They are cheapy pwm dimmers I bought off amazon. I can put the link where they are on amazon but I don't think it will tell you any information you need.

    I could go with a different dimmer but none have IR remotes that have this dimmers capabilities which I really like.

    As far as controlling it from the micro controller I'm not sure. That may be a little out of my league. My electronics knowledge is pretty basic.

    Oh and Thank you for your help!!!
     
    Last edited: Apr 27, 2013
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK, thanks for the picture.
    Without a schematic, I can't say for sure that it would be possible to control two boards from the microcontroller on one board. It may be possible but it may not be.
    My only suggestion now is for you to find someone with electronics experience who can trace out the circuit of your board. Then he, or I, could work out how to connect the boards so both regulators are controlled from the same microcontroller, if that's possible.
     
  10. galaxy

    galaxy

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    Nov 3, 2012
    Possible maybe having the 2 data lines effectively tied together on the 2 boards is an issue?
    Maybe some sort of isolation/buffering required?

    Just a guess...
     
  11. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Yeah unfortunately I'm limited on my electronics knowledge and don't know anyone that could trace it out. But in playing with it for a while it is rare when it does mess up and it seems like if I hit the "fade to off button" on the remote and then hit another brightness setting the two boards get back in sync.

    If that is the case after more testing I can live with it.

    I would like the two boards fade to off feature to actually do that in sync. It seems like one is slightly slower than the other. My guess is that will be corrected when I have the IR module wired into the boards at the same legnth of wire. Right now I have one IR module still on one board and two jumper wires to the other board. The board that doesn't have the IR module on it but jumpers wires seems to dim slightly slower.

    So my guess is if I have the IR module off the board and jumper wires from the IR module to both boards they each will see the same resistance. It's the only thing I can figure as to why there is a lag time between the boards for the fade to off.

    Would that make any sense?

    Oh and Galaxy how would the isolation/buffering be accomplished?
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Bzzt!
    I would expect them both to behave the same, because all timing should be controlled by the 24 MHz crystal. I don't know why one would fade out more slowly than the other. But it's not because of wire lengths (unless the wires are thousands of miles long!)
     
  13. galaxy

    galaxy

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    Nov 3, 2012
    Ha !! Painted myself into a corner there. !
    I am only just getting back into Electronics after a quarter of a century or so..I am a bit rusty.
    In the old days I'd probably use something like a 4050.
    Kris might chime in here and tell me if I am off with the pixies...
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You could buffer the receiver output but I doubt very much that it would help.
    Yes, you could use a CD4050, or perhaps a PNP emitter follower. I won't draw a diagram unless you (Mustwin351) really want to try it, because I don't think it would help.
     
  15. Mustwin351

    Mustwin351

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    Apr 10, 2013
    No it's alright kris don't worry about drawing it.

    Oh i forgot if one led strip is longer than the other would that be the cause of the time lag in the dimming?

    Also if I wanted to measure the current draw that my leds are drawing. Would it be possible with a NON-rms meter using my probes in series to measure the current draw on the line side before my 12v power supply.

    In other words between my 120v wall outlet and the power supply?

    I've done this but it seems to be drawing less than it should according to the specs on the led strips.
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I don't think so. It depends on exactly how the control boards works. Try swapping the LED strips and see whether the delayed dimming follows the LED strip or stays with the same control board.

    That wouldn't be very accurate. The amount of power used by the power supply and the control board aren't known and they could vary in unpredictable ways. A better way is to connect a DC meter in series with the LED strip. This should give a fairly accurate measurement even if the LED drive is pulse-width-modulated.
     
  17. Mustwin351

    Mustwin351

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    Apr 10, 2013
    Not sure if it helps but I took a reading between the wall and power supply with the leds off and got 5 watts.

    So even without a high dollar meter I could get an accurate current draw reading in series with the leds? I figured the square wave nature of pwm would make it inaccurate?
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The multimeter will respond to the average DC voltage across the current shunt that is in series with the LED strip. (This current shunt is inside the multimeter if you use it on a current range.) It should be fairly accurate.
     
    Last edited: Apr 28, 2013
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