Problem with unreliable trigger of 240V remote GPO

Discussion in 'The Projects Forum' started by ian-glids, May 28, 2011.

  1. ian-glids

    Thread Starter New Member

    Nov 1, 2009
    3
    0
    G’day all,

    I would like some assistance with a circuit that is giving me some trouble. The circuit in question is a Remote 240V Controller that I use to operate a winch to pull a caravan up a narrow driveway. I got the remote transmitter and receiver units (wireless) from a neighbour, and he helped with the design of the circuits to operate the relay for the 240V GPO, but he has moved away. Also, I have heard he recently had a heart scare, and I would rather not trouble him at the moment. I have a basic understanding of electronics, and can solder/build circuits from circuit diagrams, but I do not understand enough about the design of circuits to be able to fix the following problem.

    The receiver emits a series of beeps when the transmitter sends a signal, and I can hear the beeps from 35 to 40 metres away, but the rest of the circuit is not reliable enough as the relay does not always operate. If I am starting the winch, it is not a big deal as I keep pressing the transmit / operate button until the relay kicks in. But occasionally the relay does not disengage when I want to stop the winch, and that can be a disaster. As the driveway is so narrow, I cannot get to the winch in a hurry if things go wrong, and I have already pulled the caravan into a fence once when the winch would not turn off. Note that the circuit is set up for latching the relay – the same transmitter button should start and stop the winch.

    One confusing aspect of this problem is that it appears to depend on distance. The relay operates fairly reliably when the transmitter is close (say within 10 to 15 metres) but is not so reliable at full range - BUT the beep can be heard at most ranges. Why would the beeper work at all ranges, but not the relay? - I assume if the beep sounds it means the receiver has fully triggered, but I have not been able to confirm this.

    The attached diagrams show two circuits. I cannot remember why we changed from the ‘ORIGINAL’ to the ‘REVISED’ circuit. The circuits do not show any details of the transmitter or receiver as these are proprietry devices. We have only tapped into the receiver's output to trigger the rest of the circuit. I am happy to purchase new components and revise the circuit board as I need to cure this problem. I have a number of BTA41-600B and BTA25-600B Triacs if they would prove useful.

    Any suggestions or circuit improvements would be most appreciated.

    Cheers,
    Ian
     
  2. ian-glids

    Thread Starter New Member

    Nov 1, 2009
    3
    0
    A bit more info...

    I just conducted some tests using some high intensity LED's connected to a battery via the relay terminals.

    The LED's came on regularly when I 'started' the system with the remote, but when turning the system 'off' the LED's often turned off, then immediately turned back on. The 'real life' equivalent of this would be that the winch would APPEAR to not turn off, but may in fact be turning off and immediately re-starting.

    Therefore, the problem may be in the part of the circuit associated with alternating the action (is this a flip-flop?) of the relay.

    Also, I failed to mention in the original post that for safety the circuit was designed to always start with the winch 'off' - ie: Plug into mains, turn on mains, winch will not start until remote is used.

    Cheers,
    Ian
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,055
    Whatever you do, you should change that basic design to NOT latch. It's just too dangerous, as you've seen. You're lucky - it could've been worse. (pets, small children, etc.) I think it would be fine, and much safer, to make the winch only operate while the button is held down and release any time it does not see a signal. The transmitter may be sending bursts, so there may need to be a brief "coast" that would keep the winch running between bursts. But if it misses a burst or two, it should disengage. I believe a 555 timer circuit could be easily adapted to this particular task. It can be set to stay on for an adjustable time after receiving a trigger and then go off if another trigger is not received to start the cycle over again.

    Others here will have to help you with the rest of the circuit. One thing the revision does is to get more power to the relay. It probably didn't work without that change. Adding the 40106 Schmitt trigger was likely to help with converting the receiver signal to a clean switching signal. I believe my 555 timer approach would eliminate the need for both the 40106 and the 4013 flip-flop. Not sure about the impact on start-up though. Again, we need some experts here.
     
    Last edited: May 31, 2011
  4. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Well, I can see why your circuit is working erratically. The gate of the FET is not connected properly. The 100K should be connected between the Gate and GND. There also should be a small ~ 100Ω resistor in series from the 4013 output to the gate.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    A small cap (.1UF) from the gate to GND would also be a good idea. It will reduce susceptibility to electrical noise.
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I just realized that I don't see a Piezo in your circuits. Are you sure it's not in the receiver module that's not shown?
     
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