Remote control via cable using IR encoder and decoder

Discussion in 'Analog & Mixed-Signal Design' started by Massimo Martini, May 18, 2018.

  1. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    Hi! i need to switch some relays for an antenna switch on the roof and i cannot pass extra cables so i want to send the control signals from my coaxial cable.
    I was thinking to use ICs for infrared remote control PT2262-IR (encoder) and PT2272 (decoder) to send the 38KHz signal on the cable.
    Do you think it will work?
    Here below is the diagram from the datasheets, i need to figure out how to inteface the cable to the ICs once i have removed the IR leds.
    On PT2262 i am not sure if i can just remove the ir led and connect the cable there still using the two transistors Vt1-Vt2; same thing on PT2272
    [​IMG]
     
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Assuming it is ok for the 38 kHz signal to completely swamp/destroy the antenna signals briefly, then your idea should work.

    The receiver is relatively simple. It is connected continuously to the cable by a coupling network or preamp that presents a very high impedance to the other signal frequencies going to/from the antennae. BTS, are the signals TX, RX, or both?

    The transmitter is a bit more complicated, depending on how automated you want things to be. Most simple is that the transmitter output is connected directly to the cable center conductor through a SPST switch. Close switch, send command, open switch. If you want the transmitter connected all the time, then again it needs to go through a network that does not load the cable at the other signal frequencies. The 2262 OUT pin probably will need an external bipolar driver such as an opamp rather than an open collector.

    What is the coax cable impedance, and is it terminated in its characteristic impedance?

    ak
     
  3. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    Hi AnalogKid, thank you for your reply,
    It is for receiving antennas and i do not want it to be connected to the cable central conductor all the time; i also thought to keep a pushbutton pressed when i want to connect it to send a command.
    The coax impedance is 50 ohm and the lenght could be around 35 meters but some antennas are open dipoles and others could be folded dipoles; could this damage the output of the ic?
    Should the connection between the box and the receiver have a high pass filter to prevent the 38KHz going to the receiver and damage it? alternatively i could use a a SPDT relay activated from the pushbutton.

    Honestly i had two alternatives and the coax cable is not the preferred one but i wanted to keep things simple. The preferred alternative is to make this with the 12v DC wires that go from my desk to the antenna, so i can also use this system to rotate a dc motor that adjust the variable capacitor of the loop antenna untill i get the maximum signal and i can also use it for transmitting. The PT2272 is available temporary or latch and i can have both on the antenna side switching the pin coding of the transmitter. If you think that with the DC wires is also possible and simple i could go directly with this.
     
  4. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    A SPDT relay could do both functions - connect the RC transmitter to the cable, and disconnect the cabpe from the radio receiver inputs. I assume there is some kind of power source already at the antennae to power the receiver circuit - yes?

    ak
     
  5. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    Yes, correct, they are the two wires that i was talking before, they carry 12vdc from my desk to the antennas
     
  6. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    When in posted here i also have sent an email to PTC explaining what i want to do and asking how to interface the coaxial cable to the two IC.
    Today i have received the reply:
    Thank you for your interest in PTC product.
    Customer Dept. have confirmed with our engineer. He replied your technical question as below:
    In principle, it's possible to achieve customer's application, but I can't guarantee that is no problem due to I don't have demo board on hand. Please try to connect the output pin DOUT of PT2262-IRS IC to input pin DIN of PT2272 IC chip to check it operating normally or not. Thanks!
    o_O
     
  7. ArakelTheDragon

    Active Member

    Nov 18, 2016
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    Why not a WiFi module?
     
  8. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    Too far behind walls, not reliable. This remains a second option to test.
     
  9. ArakelTheDragon

    Active Member

    Nov 18, 2016
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    If the walls are drywall its like cardboard.
     
  10. Massimo Martini

    Thread Starter New Member

    Dec 2, 2017
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    Unfortunatly buildings in Italy are made of hollow bricks for separation walls and reinforced concrete for load-bearing and exterior walls.
    Whatever it is i like to make it as described, not something else :)
     
  11. be80be

    AAC Fanatic!

    Jul 5, 2008
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    It's on the roof don't got worry about walls lol it up what's in the ceiling LOL and on the roof.
     
  12. be80be

    AAC Fanatic!

    Jul 5, 2008
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