IR remote

Discussion in 'General Electronics Chat' started by xdrxs, Apr 1, 2014.

  1. xdrxs

    Thread Starter New Member

    Apr 1, 2014
    2
    0
    Hello!

    This is my first post so if I make any newb mistakes regarding forum protocol, please forgive me.

    I am in the middle of one of my first electronics projects, which involves building my own IR controller for some multi-color LED bulbs that came with a remote to control color, brightness, and toggle on/off.

    I took apart one of the "APA 1616" remotes and this is what it looks like:

    I hooked up 2 AA batteries in series to power circuit board, and then touched a piece of aluminum foil to the different contact points on the front of the board. The light bulb changed colors as expected when I completed the circuit, but not for all buttons.

    None of the buttons on the right side of the remote worked, including "ON". All the other buttons not on the right column of the remote did work when I pressed the piece of foil to the contact point.

    My question is this:

    1. Why didn't ON or any of the buttons on the right side work, and how would you go about diagnosing further?

    2. What is thing in the red circle on the back of the circuit? I think it's an IC, but there is a strange black covering on it that I can't peel off.

    Thanks
     
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  2. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    I can't tell you why, but I can tell you what. That black bump is a protective coating called, "glob top". Do not attempt to remove it or you will destroy the circuits.
     
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  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Have you reassembled the remote to see if it's still working?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,120
    3,046
    The buttons on the right might not have a function, or your testing was not able to detect the function.
     
  5. mwalden824

    Member

    Mar 6, 2011
    51
    2
    You could have damaged the digital circuitry under the glob if you tried to remove it like #12 said, unless they didn't work from the beginning. But also it could be some open circuit trace in the board. You can test with a DMM on the ohmmeter setting. There are two separate traces that get connected when a button is pushed as you can see, so pick one, follow it as far a you can go, back to the blob if possible, and put one lead of the DMM there and the other back at the button for that trace (near the blob you need to push you sharp probe hard enough to cut through the resist). If it shows a resistance, very small, but something, then no short. But do it again for the exact same button for the other trace. If both are fine for all the right side buttons then it has to be the digital circuitry under the blob.

    Most of those types of button use a sort of matrix style setup where say if you have 16 buttons, then you have four traces going horizontal and 4 going vertical, well they don't have to be that way on the circuit board, but that is the way it works. The digital logic or microcontroller will apply a voltage down each of the horizontal or vertical traces at a time then measure the opposite (vertical if voltage was applied to horizontal and vice versa) to see if the voltage appears. You see what I mean?

    As an example it would start at the top horizontal trace and apply a voltage there, then see if there is a voltage at any of the four vertical traces one by one or all at the same time if it isn't a processor under the blob and just digital logic, if it doesn't find one, it moves down and applies a voltage to the second horizontal trace and then repeat the process until it finds where a voltage is measured and by knowing the row and column you know the button.

    My whole point of explaining that above was that since the right side buttons don't work, maybe the trace is broken somewhere for the right column of the matrix. But I didn't look at the board close enough to see if this was the actual implementation. They could just as very well use two pins for each button, or several smaller matrices, etc. It's just that the matrix method saves some pins and traces and the description above is just one way they could do it. But really there should only be two problems, a broken trace somewhere, or a screwed up digital circuit under that glob. If it is the latter I guess you could cut it off and put a microcontroller on there and kind of rig it up, or make a new redesigned PCB the same size that will fit in the case, I don't know how far you want to take this project. But if it is just a broken trace, and you found where it is then you could scrape off the resist and solder a small wire over it.

    Later,
    Michael Walden
     
    Last edited: Apr 1, 2014
  6. xdrxs

    Thread Starter New Member

    Apr 1, 2014
    2
    0
    @mwalden824:

    Thanks for your detailed reply. I *kinda* see what you're saying, and if I hooked up a DMM to the circuit I might grok it more deeply. I just got my IR sensor in the mail, so I'm going to move on and get the IR signals and then duplicate them with my microcontroller and IR led.

    I did reassemble the remote, but still the right side of buttons does not work so probably I damaged it somehow in opening it. I guess I'll leave it at that and move on with the project.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    I've analysed the PCB photos. It is definitely matrixed in banks of 4 across, and the right hand column of 6 buttons is connected to one trace that goes to the IC blob.

    That trace has a test point, at the very bottom left corner of the PCB in your second photo. You should check continuity of that trace back to the IC blob.

    Also the conductive paint through-via might have failed (the white circle, also bottom left corner). They use that paint to make all the dark grey "tracks" on the front of the board (and the vias), there is only copper on one side.
    :)
     
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