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RF circuit with HT12E and HT12D

Discussion in 'Radio and Communications' started by krishmidhun, Sep 20, 2016.

  1. krishmidhun

    krishmidhun New Member

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    Hi, I have made a simple RF circuit with HT12E and HT12D. My problem is that when I press any switch on the transmitter and cut power to the transmitter by holding push switch, the receiver end is still showing a LED output. I want it to go to the default state of all LEDs off whenever transmitter goes out of range or power to it is cut. Please help me on this.
     

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  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Have you not tried reading the datasheet?

    Which is on page 4.
     
  3. RadioRon

    RadioRon Well-Known Member

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    The HT-12D has a latched output so the circuit is, unfortunately, functioning as designed. To change the function to match your goal, perhaps we can add some additional circuitry to the transmit side. For example, it would be possible to add a power on/off circuit to the transmitter so that when the power is switched off, the transmitter sends one last message but with the data word forced to be "1111". In order to do this, we would need to add a local power storage filter (for example a series diode following by a larger value capacitor), plus a circuit to sense when power has been removed from the tx which signals the data bits to become all ones, and a gate or transistor at each data input controlled by this sensing circuit.
     
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  4. dave

    Dave New Member

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  5. krishmidhun

    krishmidhun New Member

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    I have tried using VT as output. but the problem is the output from the VT is flickering some times. Is there any solution to get stable the output from VT
     
    Last edited: Sep 20, 2016
  6. krishmidhun

    krishmidhun New Member

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    can't we do any changes in receiver end? instead of transmitter side. because the transmitter should be small in size, hence i can't add anything to it.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    VT signifies a valid signal received, so any errors means it will drop out - but what EXACTLY are you wanting to do?, and why are you using IC's unsuited for your purpose?.

    We get endless questions about these devices here, and always because people are trying to use them for the wrong purpose.
     
  8. RadioRon

    RadioRon Well-Known Member

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    The changes to the transmitter would be very modest. I suggest the circuit in the attached figure as a starting point, although I admit it is a bit crude. In that circuit, D1 and C insure that power continues to be supplied to the encoder and transmitter for a short time after 5V is removed. However, in that time, Q1 - Q4 are turned off, so the code that is sent is "1111" for that short time. ht-12b006g.gif
     
  9. krishmidhun

    krishmidhun New Member

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    What i am planning to make is a "passive keyless start" for my bike. There will be a RF receiver which i have made using HT12d and a RF remote with HT12e. When the remote present in the range of receiver, a relay connected to receiver should latch and dislatch when remote will go out of the range.
     

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