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Help in converting a wireless doorbell into a remote gate switch

Discussion in 'General Electronics Discussion' started by elvislives, Sep 28, 2015.

  1. elvislives

    elvislives

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    Sep 28, 2015
    Hi,

    I have had loads of problems with my video intercom for my gate opener. It is wired, and the wires are shot. However, I can't install new wiring without digging up loads of concrete. I have tried a few wireless intercoms, but they all seem to be next to useless.

    As a short term measure, I fitted a wireless doorbell to the gate post so that at least we know when someone is there.

    I then decided that I should buy another wireless doorbell (as a cheap temporary measure) and use it the other way round so that when someone rings the bell, we can press a button inside the house and make the gate open. I obviously cannot simply wire it up to the speaker or the led light, as the gate will start dancing to the sound of the doorbell.

    What I want to do is work out where I can solder some wires to so that I can connect the bell receiver unit up to the button press of the gate opener. The gate opener side of things is fine, I know where this should be connected. It is "tapping" in to the circuit board of the bell receiver that I am not sure about.

    What I need is to get a single signal to indicate that the bell was pushed.

    I have attached a picture of the circuit board. There is a small PCB soldered on to a larger PCB, and I believe that the smaller PCB is the wireless receiver. However, I cannot work out where to connect the wires.

    Would any of you geniuses be able to work it out from the attached picture?

    Thanks in advance for any help.
     

    Attached Files:

  2. Old Steve

    Old Steve

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    Jul 23, 2015
    That won't be easy simply from the photo you provided. What are the chips?

    You need to let us know what the markings are on each of the three individual chips shown, for starters.

    I suspect that the DT connection on the receiver module might be the key.
     
  3. elvislives

    elvislives

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    Sep 28, 2015
    Thanks Old Steve.

    I left the unit on the side this morning, and don't have it with me! I will take a look tonight when I get home and update.
     
  4. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    Simply remove the speaker and connect a diode and 100u to the lands and put 100k across the 100u.
     
  5. Old Steve

    Old Steve

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    Jul 23, 2015
    That makes sense. I was thinking more of taking the output pulse from the RF module, but your method should work.
    Either will provide a short pulse.
     
  6. Old Steve

    Old Steve

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    Jul 23, 2015
    elvislives, what voltage does the gate opener need the pulse to be? Is it a 5V circuit, or higher?
     
  7. elvislives

    elvislives

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    Sep 28, 2015
    Thanks for the posts guys.

    The chips are (top, middle & bottom referring to my initial image)

    Top = SXD033B
    Middle = NT200M
    Bottom = PT4303-S

    The gate opener control board is a CB24. The manual is here:

    http://manuals.easygates.co.uk/PDF/liftmaster/cb24-englishonly.pdf

    It is a 24V unit. The doorbell unit gives a 3V signal, and that was to be my next question! I have uploaded an image showing where the connection goes.

    CB24.GIF

    I was playing around last night, and I believe that the pin that I have highlighted with a blue rectangle in the attached pin gives a 3V signal when the bell is pushed.

    SXD033B.jpg

    Am I better off using the highlighted pin, or is Colin's suggestion better (which will be much easier for me to solder with my £5.99 soldering iron?
     
  8. Old Steve

    Old Steve

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    Jul 23, 2015
    I think it will be a fairly simple matter to connect a transistor between the "Single Button" and "COM" contacts on the gate opener to trigger it.

    I can't find any data on the middle chip, the NT200M. I would have trouble soldering to that pin too, (bad eyesight), so we'll forget that option.

    On the doorbell unit's RF board, as I suspected, the PT4303 chip receives the RF signal, decodes it and pin 11 is the data output pin.. (I use PT2272 chips from the same company, 'Princeton Technology', in my RF receivers, for decoding.)

    Although your multimeter might not show it due to the short pulse length, either the "CE" or "DT" connection where the RF board connects to the main board will carry the decoded signal to the main board. If you do a continuity test with your multimeter, from the PT4303's pin 11, to each of these in turn, you'll soon find out which is the output. My guess would be the "DT" connection. That's an easy point to solder to for driving a transistor to switch between the gate-opener contacts, providing the pulse is long enough. (The PT2272 has a pulse about 5mS long, so the PT4303 is probably similar in that regard.)

    Having said that, Colin's method would provide a longer trigger pulse. I would personally take the trigger from the PT4303, because it's more 'correct', and it provides a clean, sharp pulse, but that's just me. :D

    I'll let you choose between Colin's and my suggestions. I'll draw up a diagram for each and post it here shortly.

    Edit: Actually, as soon as I started to think about it further, I struck a small problem with using Colin's method. The voltage across the speaker terminals probably won't be referenced to ground, making it harder to switch a transistor with it, so I'd try my method for that reason too, if I was doing it.

    I'll only draw a diagram for my method for now, dependent on you testing and discovering which RF board edge connector is connected to it's PT4303 chip's pin 11.
    Colin might want to draw something up for his.......

    Either way, it might take a couple of attempts to get this right, depending on how long a pulse is needed by the gate opener trigger.
     
    Last edited: Sep 29, 2015
  9. Old Steve

    Old Steve

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    Jul 23, 2015
    Just in case you don't know which is which, I've marked the PT4303's pin 11 here:-

    pt4303.jpg
     
  10. elvislives

    elvislives

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    Sep 28, 2015
    Thanks Old Steve.

    I tried the continuity test, and neither CE or DT pass the test, which is strange. Here is a clearer image showing the PCB. It looks as though it should be DT, but it goes through a resistor? Would that break the continuity test? I wouldn't have thought so.

    IMG_1679.JPG
     
  11. Old Steve

    Old Steve

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    Jul 23, 2015
    Right, "DT" it is. I guessed right. That's a 1K resistor. Your continuity tester probably won't register that as 'continuous'. If you measure between pin 11 and "DT", on a suitable resistance range, (2K?), you should measure 1K resistance.

    Just thinking about it, you might get away with Colin's method, without a transistor, in which case the lower diagram below could work. Since it's easier to implement, you might want to try it first.
    Otherwise, the top diagram will do it providing a longer pulse isn't needed.
    Let me know how you go. If you use the first method, and the pulse isn't long enough, it's possible to stretch it a bit.

    Reading the manual, since the "Single Button" input is for "open", "close" and "stop", it's important that we only get a single pulse.

    Gate Opener Trigger V1.JPG

    Edit: Ignore the "CE" on the first diagram, now that we know it's the "DT" connection. And the on-board 1K resistor won't affect the circuit I drew, it will still work fine.
     
    Last edited: Sep 29, 2015
  12. Old Steve

    Old Steve

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    Jul 23, 2015
    I wasn't thinking clearly about Colin's circuit. Don't try it as I presented it!!!
    I don't know what I was thinking. It definitely needs a transistor. :oops:
    (It needs to connect between "Single Button" and "COM", not put a voltage between them.)

    Use the top diagram, not the bottom one.

    Edit: I hope you didn't run straight off to try Colin's method. It might possibly even cause damage to the gate-opener's inputs, applying a small voltage to them, although I doubt it.
     
    Last edited: Sep 29, 2015
  13. elvislives

    elvislives

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    Sep 28, 2015
    Many thanks for the excellent advice Old Steve. It sounds as though the top diagram is the way to go, and will be easy to solder onto the DT part of the PCB. I will give it a go later and see if it works and let you know.
     
    Old Steve likes this.
  14. Old Steve

    Old Steve

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    Jul 23, 2015
    Excellent, I'm glad you saw my warning. I'd hate to recommend something that might cause damage. The top circuit is completely safe. Let me know how you go.
     
  15. PTaylor

    PTaylor

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    Jan 26, 2013
    Old Steve, and/or anyone else that has knowledge and experience with the PT4303 and/or that"family" of chips.
    I know this is an old topic, maybe I should start a new thread, but while searching the internet for information on this chip, I found this discussion.
    Right now I've got a PCB that has a PT4303 chip on it and an unmarked, 8 pin SOIC chip. After tracing everything out, I'm 99% sure the unmarked chip is an 8 pin microprocessor of some type. The unknown chip has two traces that go back to the PT4303. those traces equal the CHIP ENABLE and DATA OUT of the PT4303. So, my thinking is that the unknown chip is pulling the CE line high during typical operation, and receiving data from the the PT4303 on the DO line.
    My question is this, what "information" is the PT4303 chip put out? meaning, is there some communication protocol that it uses to pass data? Serial or something else? just a line of pulses?
    If I wanted to replace the uP with something of my own, how would I "talk" or interpret the information coming from the PT4303?
    I've downloaded their datasheet and it doesn't describe what to expect on the DO line. I havent been able to find any other info or projects using this particular chip.....
     
  16. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    You really need a 5v CMOS relay between each project. Use the transistor to drive the relay.
     
    hevans1944 likes this.
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