Troubleshooting an IR remote relay circuit

Discussion in 'The Projects Forum' started by Jester8, Apr 22, 2015.

  1. Jester8

    Thread Starter New Member

    Apr 22, 2015
    1
    0
    Hello,

    I am working on constructing a circuit to control devices with an IR remote. The schematic is displayed below.

    upload_2015-4-22_13-49-30.png

    I am having a problem that I can't figure out. I have checked my connections over a few times and haven't found any problems. Here is a link to a video of the circuit showing the problem.



    The circuit responds to the remote but the relay is "sticky" (in the video the response you see if from pressing the button once each time.) I have tried different remotes with the same issue. Is this some kind of debouncing issue? I have also tried with multiple relays to rule that component out. I would really appreciate any suggestions you might have! Thank you
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,777
    1,103
    What signal are you transmitting from the remote?
    Are you using a standard TV remote?
    Since Q1 in your circuit has no resistor to limit base current, there is a good chance either Q1 or the open-collector output transistor of the TSOP1738 will be damaged. I would suggest ~10k.
    You are asking the poor little CD4017 to provide a lot of output current from its Q0 and Q1 outputs. It will struggle to do that without its output voltage sagging. So the transistor Q2 may not be getting enough base current to turn it on fully and operate the relay reliably. Consider replacing the CD4017 with a 74HC4017.
     
    Last edited: Apr 23, 2015
  3. Retiredguy

    Member

    Feb 24, 2007
    28
    5
    Jester,
    From your post, I assume that by "sticky" you mean the the relay remains on after you press a button of your remote. And by your problem remaining using "different " remotes, I also assume that you are using TV remotes or something like that. That being said, those type of remote controls output a binary code in the form of 1's and 0's which are the clock source of the 4017. From the data sheet, a reset will set Q0 high and turn on D2, the first clock pulse should make Q0 low and Q1 high turning on D1 and the relay, and one more pulse on the clock line, Q2 goes high thereby resetting the 4017 turning off the relay and D1. That is how the circuit is supposed to work. So if you are using a remote that puts out an odd number of 1's in it's code the relay will hang. I would suggest that you build the IR transmitter that was on the web page with this circuit. That should fix your problem.
    Mike
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,648
    632
    For starters, the output of the TSOP1738 is 100k to V+ connected to the collector of an NPN transistor with its emitter grounded. Every time the output goes low it tries to short V+ to ground through the base-emitter junction of Q1!

    If nothing else, putting a resistor between the output of the TSOP1738 and C2 should help keep from killing Q1 and/or the TSOP1738 and probably clean up V+ which might result in more predictable operation.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
    1,247
    With 100 uF on the 1738 output, it is acting as a missing pulse detector with an effective time constant of over 20 seconds. So there is no cycle-by-cycle chatter on the input of the 4017. However, the clock edge into the 4017 is pretty slow due to R2-C3. This could appear as noise on the clock input despite the long time constants.

    ak
     
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