Remote control problems

Discussion in 'General Electronics Chat' started by rjjenkins, Dec 9, 2012.

  1. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    Please would you have a look at the attached circuit (hand drawn, sorry)

    It's intended to drive a lamp using a remote control unit. The unit is this one

    http://www.ebay.co.uk/itm/433MHZ-4-...6827?pt=UK_Gadgets&hash=item4ab87ca6db&_uhb=1

    I want to run the lamp and remote on different circuits and isolate them using a 4N25, and to drive the lamp using a mosfet.

    The remote unit toggles, so that pin 7 of the rx goes high when the tx button is pressed and stays high until it's pressed again. This all works fine. However, the lamp only stays on so long as the button is pressed, i.e. it does not toggle.

    What am I doing wrong please?
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Tell me, are u meddling with live voltage here?
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    If the lamp lights when Tx is pressed but turns off when released, the circuit is working, just not toggling.
    Post a datasheet for Tx/Rx.
     
  4. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    There is no datasheet unfortunately. However, the remote itself DOES toggle - i.e. if I disconnect it from the rest of the circuit, it works perfectly. So it's something between the rx and the lamp that is not right.
     
  5. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    No, batteries only as shown in the circuit
     
  6. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    How are you determining it toggles when disconnected?

    It may be Rx can't properly drive the Led in the 4n25
     
  7. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    with a multimeter.
    It can drive an ordinary LED though so that doesn't seem likely
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Have you actually connected an LED with a 360 ? ohm resistor to verify this works ?
     
  9. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    Not with the resistor actually, no. I will. I think maybe the resistor is too high.
     
  10. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    I've shorted out the 380 ohm resistor on the circuit and it now works, so I guess the rx output was just too feeble. Am hoping that it's not now too much for the LED but I suspect not.
     
  11. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    I don't think it's ok. Even in the decoder ICs datasheet they drew current limiting resistors (last page). You could damage the opto or the decoder IC.

    http://www.sc-tech.cn/en/SC2272.pdf
     
  12. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    Try sneaking that 380 down a bit at a time. I calculate 300 ohms..try 270, etc.
     
    rjjenkins likes this.
Loading...