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remote control extender.

Discussion in 'Electronic Basics' started by Johan Wagener, Sep 28, 2003.

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  1. I built the circuit as shown on
    http://www.mitedu.freeserve.co.uk/Circuits/Interface/irext.htm.

    I could not get hold of the photodiodes they used in this circuit.

    I used the following components available from http://www.fort777.co.za/

    Infra red emitter:

    Peak wavelength: 940nm
    Forward voltage at IF = 20mA: 1.6V
    Forward current max.: 100mA
    Power dissipation: 100mW
    Radiated angle: 30°

    Receiver photodiode:

    High sensitivity infrared photodiode in side-looking TO92 package.
    Black (infrared transparent) epoxy resin package.
    Light current typically 75uA at 1000 lux.
    Matching transmitter LIR151.
    The cathode is the short lead.
    ecifications

    Peak wavelength: 900nm
    Open circuit voltage: 0.35V
    Acceptance angle: 120°

    The receiving part of my circuit seems to work (led flashes when remote is
    used) I can't seem to get the emitting part to work. The units (tv,hi-fi,
    ect) simply does nothing even when the diode is placed right in front of its
    IR.

    I can's seem to find the datasheet for the SFH2030 used in the circuit

    Please help
     
  2. Fred

    Fred Guest

    I assume LED0 is the IR transmitting IR LED. I suspected it may have
    flashed at least the once bearing in mind that you have a 27R series
    resistor and a power supply of 12V. This would give a current of 3-400mA, 3
    to 4 times rated current.
     
  3. I did actually lose one LED because of this. It flashed quite a while before
    it fried. I changed the value of the resistor to 1k. That however did not
    solve the problem concerning the unit not emitting IR
     
  4. Try using a camcorder to determine if the transmitter is at least flashing.
    I've done this before and it works quite well.

    Richard
     
  5. Fred

    Fred Guest

    I would change this to 220R to limit the current to 50mA which should be
    safe.

    How did you see LED0, the IR led flash. Was it incandescent? I would use a
    video camera or a camcorder to check the output of the IR LED.
     
  6. Anand Dhuru

    Anand Dhuru Guest

    Hi,

    Richard's suggestion about the cam corder is the best place to start.
    You could also use a web-cam if you have one connected to the PC for
    the debugging.

    Then, for any project invoving a commercial modulated remote (like the
    ones which you are trying to extend), it is *much* better to use a 3
    pinIR detector module, rather than discrete components. These devices
    have all the electronics required to demodulate the signal very
    reliably, in a large variety of ambient lighting conditions, and
    reject noise to a great extent. You will get much better results, and
    the circuit is as simple, if not simpler.

    I could mail you the schematics if you are interested.

    Regards,

    Anand Dhuru

     

  7. Infrared LEDs are often rated for a maximum of 100mA continuous forward DC
    current. If the circuit is working properly like it should, then the signal
    detected from the remote will be a roughly 38kHz 50% duty cycle squarewave
    carrier frequency light signal that is further modulated by the data at
    likely less than 50% duty cycle (of the 38kHz carrier) at some frequency
    well below the carrier. Usually IR remotes will AM modulate the 38kHz
    carrier at some frequency so slow as to be very easily human detectable as
    flickering.

    So the effective duty cycle the LED should see is likely less than 25%, but
    certainly well less than 50%. So even though the 27 ohm resistor limits the
    current to something like 3-400mA, when multiplied by the effective duty
    cycle the average current through the LED will likely be somewhat less than
    100mA. If the circuit is operating properly, the LED will not be
    significantly abused...

    Unfortunately this circuit is very poorly designed in many respects. The
    circuit has novel simplicity, but pays for it in functionality/reliability
    and performance.

    If the ambient lighting conditions are too high, the circuit will constantly
    detect that and turn the output stage on full blast at 100% duty cycle
    (plain DC). Thus there certainly exists a real possibility the IR LED could
    be damaged by excessive current.

    The other really serious problem is the circuit doesn't really try very hard
    to keep the incomming and outgoing duty cycles the same. This is probably
    why the OP's implementation isn't working. While some IR receiver circuits
    might have lax input filters that will respond acceptably to a distorted IR
    signal, the OP's IR receiver probably doesn't like the distortion that
    likely will be added by the circuit. As a result is balks and doesn't work.

    A better designed IR repeater would do something more like this:

    An infrared 38kHz receiver IC (such as the Panansonic PNA4602M from Digikey)
    should first detect the remote control signal. Since the output of the
    receiver IC will be demodulated data, we will need to remodulate the data
    onto a new 38kHz carrier. Since the output of the Panasonic is an open
    collector output with internal pull up resistor, the output is inverted from
    the sent signal. We will need to invert the output signal to get it looking
    right again.

    A 38kHz 50% duty cycle (fairly high precision, +/-1kHz will likely start
    reducing functionality) oscillator will be needed. The oscillator output
    should be ANDed with the output of the inverted IR receiver IC output. The
    final output should be buffered by a fast switching small MOSFET such as the
    BSS138 to drive the LED at pulse currents of up to around 400mA (or perhaps
    more if you can insure the average current is less than 100mA). Using
    bipolar junction transistors isn't necessarily a good idea for this stage
    since they can have fairly long storage times which will distort the signal.
    At 38kHz and reasonable drive currents the effect may be minimal, but to be
    safe it is easier to just use a MOSFET. Make sure the range extender LED is
    not pointed such that any significant amount of IR light will fall on the
    detector, otherwise signal feedback will occur and the system will probably
    self oscillate.

    Even when going to all this trouble the range extender may still not work
    since the Panasonic PNA4602M or similar IR receiver IC may distort the
    signal enough to cause problems in some cases. In these instances probably
    the easiest solution to increasing range is to modify the remote control
    itself. Replace the IR LED with one that is more efficient (such as the
    Vishay TSAL6100 from Mouser), or use multiple LEDs in parallel (make sure to
    pump up the driver power to drive them properly).

    To give an idea of what is possible, using six paralleled TSAL6400 LEDs
    pulsed at 1A peak currents and a Vishay TSOP1256 receiver IC I was able to
    achieve outdoors (at night) data transmission at distances of up to an
    estimated 70 meters. Even more range is surely possible with shorter beam
    angle LEDs (or more LEDs) and perhaps some other circuit tweaks/improved
    optics.
     

  8. Well I haven't analyzed the circuit in depth, but yeah it does look like it
    definitely has the right idea. As the text indicates it would probably work
    better if it were configured for 50% duty cycle.

    Also, AFAIK IR remote controls more often operate with a carrier frequency
    of 38kHz rather than 40kHz. Certainly both frequencies along with a few
    others are used in IR remote applications, but I think the 38kHz is more
    popular. I could be wrong.

    Nevertheless since the 555 is a poor tolerance RC type oscillator it would
    probably be a good idea to use a small frequency trimming pot to allow
    yourself to tweak the frequency over the full range including 38kHz and
    40kHz to find the frequency of best performance (and perhaps much wider
    range still just in case your IR remote runs at something like 56kHz for
    instance).

    Also the IR LED driver is pretty wimpy in the schematics. I would replace
    the output stage 2N2222 with a small MOSFET and reduce the LED series
    resistor substantially. The range will certainly be reduced using it as is.
     
  9. Also, AFAIK IR remote controls more often operate with a carrier frequency
    Philips is 36, Sony and a few others 38. I don't know who uses 40. But
    the bandfilters are not *that* narrow, a 38 will work reasonably well
    with a 36 or a 40.


    Wouter van Ooijen

    -- ------------------------------------
    http://www.voti.nl
    PICmicro chips, programmers, consulting
     
  10. jibaro

    jibaro Guest

    That circuit, with minor mods for the components I had around, worked with a
    Panasonic DVD and a Sony TV. It refused to work with a Scientific Atlanta
    cable box and a Harman Kardon AVR110 system. BTW, the DVD and the AVR110 are
    the two components (located behind a wood door) that I want to control with
    this IR repeater. You could say I'm 50% there.

    HarmanKardon has been known to go out of its way on their designs.
    Could they be using a strange frenquency to carry the bitstream?
    Has anybody measured this?

    I do not have the equipment to measure, perhaps someday I will....

    Thanks.
     
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