Closed loop monitor

Discussion in 'The Projects Forum' started by RodneyB, Apr 24, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I have a GSM module that I want to use to send me a message when the power goes off and a message when the power is restored.

    The module has a closed loop monitor and I want to build a circuit that opens when the mains voltage goes and returns.

    I know I can use a 220 Volt relay but if possible would like to use something else as the relays are quite expensive.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    an opto coupler, transformer,mains relay.
     
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you VERY much I think the Opto coupler is the best option
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You want just a one-of, or are you building lots?

    I needed a remote indication of presence/absence of 240Vac recently (remote LED to show that my deep-well pump motor is running) so I used an old cell-phone charger. It puts out isolated 5V @ ~1A when connected to 240Vac, which runs an led at the end of a 100m wire run...

    Such chargers are almost free at local thrift shops. You likely have one lying in a drawer someplace....
     
  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Hi Mike

    I am Needing only one at the moment.

    What I was thinking was after the advice of the Opto isolator to from the secondary side of the transformer after the circuit has been rectified and smoothed to 24 volts to fit the Opto isolator (as per attached Diagram)

    The collector and the emitter of the Opto can be collected to the GND and IO1 which is a normally closed loop. When the circuit power goes off then the collector emitter junction will be open and that means its an open circuit sending the message.

    Hope this makes sense and will work.

    Thanks

    Rod
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Since you are using a transformer to isolate the 240Vac from the low voltage secondary side anyway, what purpose does the opto-isolator serve?

    If using a transformer, no opto is needed.
    If using an opto, no transformer is needed, although it cant be talked about on this forum.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    It should work exactly as drawn. But it is a lot less work if your replace TR1, BR1, and C1 with a cell phone charger as Mike suggested.

    ak
     
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  8. Papabravo

    Expert

    Feb 24, 2006
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    You don't need the opto for isolation, that is true, but it makes an acceptable level shifter to whatever Vcc your control system uses. What you get from the half wave rectification action of the diode is a 60 Hz. square wave. We always measured the period of the waveform to conclude that AC power was present.
     
  9. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I thought I needed the Opto so that on IO1 the unit is connected to Ground whilst the mains is on. When the mains fails, IO1 is open and a message is sent.

    I have attached the Installer manual of the GSM module
     
  10. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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  11. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    The attachment
     
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