Closing a switch using a 3.3vdc relay

Discussion in 'The Projects Forum' started by s_malt, Jan 1, 2014.

  1. s_malt

    Thread Starter New Member

    Jan 1, 2014
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    0
    I'm working on a project to control a garage door using a ip camera's i/o port to "press the button" on a opener remote control.

    The i/o port gives me 3.3vdc that can be applied in an on/off manner or in a momentary pulse (configurable). The i/o port has a max load of 50mA.
    (pin 2 - 3.3vdc, 50mA max load)
    (pin 4 - digital output, internal connection to ground when activated, floating (unconnected) when deactivated. If used with an inductive load, e.g. a relay, a diode must be connected in parallel with the load for protection against voltage transients)

    The opener remote control uses a 3.3v battery. I've identified the momentary switch on the remote and soldered leads to the negative and positive pins that will actuate the door when shorted.

    I'm stuck at identifying the relay and protection diode required in this scenario.

    Any help or suggestions would be highly appreciated. TIA.
     
  2. #12

    Expert

    Nov 30, 2010
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    The protection diode is any small diode that can carry as much current as the relay coil needs, which means just about any small diode like 1N4148 or 1N914 or 1N 4001 through 1N4007.

    Here are some relays. There are only 4 of the 3.3V, so I expect that most people use the 3 volt relays because the transistor that is firing the relay and needs protection uses up .3 volts for itself.

    http://www.mouser.com/Search/Refine.aspx?N=254125
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    be very careful.. The 50mA output max might/will be a problem.. Most 3V relays need more than that..
    You will likely have to use a transistor driver for the relay.

    An optocoupler will likely be a better solution.
     
  4. #12

    Expert

    Nov 30, 2010
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    No. It can be done. I just found (2) 100mw relays on that page I pointed to.
    They aren't going to switch 30 amps on and off, but they will get this job started.
     
  5. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    try this circuit with an opto but using a separate 12v supply....you may or may not need a series resistor for the opto if your unit has one already.....
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    May or may not need a relay at all..
    When I said opto I meant ONLY an opto..
     
  7. #12

    Expert

    Nov 30, 2010
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    Many ways to skin the cat, there are.
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Yoda? Is that you? :D
     
    #12 likes this.
  9. alexfreed

    Member

    Oct 8, 2012
    72
    10
    It appears that the device to be controlled is a battery powered remote. So I see no reason at all to isolate it from the camera by either a relay or an opto-coupler.
    Just take an NPN transistor, say 2N2222. Connect the emitter to the ground of the remote, collector to the other side of the button (assuming the button has one side on the ground.)
    In any case the transistor will be across the button. Emitter is also connected to the ground of the camera and the base - to the i/o pin via a 10K resistor.
     
  10. s_malt

    Thread Starter New Member

    Jan 1, 2014
    2
    0
    The device to be controlled in this case is indeed a battery (3.3v) powered remote control.

    My concept is to be viewing my garage door through this camera and have the ability to trigger the digital i-o to open or close the door. The camera interface has a GUI control to manually trigger the digital i-o.

    The camera is an Axis M1054 IP Camera. The i-o block on the camera provides (schematic image attached):

    GND - pin 1 - Ground

    3.3 V DC Power - pin 2 - Can be used to power auxiliary equipment (note: this pin can only be used as power out) - Max load = 50 mA

    Digital Input - pin 3 - Connect to GND to activate or leave floating (unconnected) to de-activate. 0 to +40 V DC

    Digital Output - pin 4 - internal connection to ground when activated, floating (unconnected) when deactivated. If used with an inductive load, e.g. a relay, a diode must be connected in parallel with the load for protection against voltage transients) Max load = 100mA; Max voltage = +40 V DC

    On the camera - I tested the pulse mode of the Digital Output by connecting an LED scavenged from an outdoor solar lamp between pin 2 and pin 4. Initiating the pulse caused the LED to turn on momentarily - so I'm confident the i-o port works.

    On the door opener remote I located the momentary button switch and identified the positive and negative side of the switch. When I short these two points, the door actuates.

    On the Liftmaster/Chamberlain door opener itself (the big motor mounted to the ceiling) I identified the negative and positive bell wire leads coming from the wall mounted control panel, but shorting these did not result in the door actuating. I really don't know what the panel is supplying on these outputs - but seems to be more than a doorbell switch. This is why I opted to go the route of controlling the remote. Even Liftmaster's own Internet control device (HomeQ) is in essence just a remote bonded to the opener.

    I've ordered the components #12 pointed me towards and I receive them tomorrow. I selected the 9814-03-00 Reed relay and the G6C-2114P-US-DC3 Omron general purpose relay.

    I was hoping to try alexfreed's direct-transistor suggestion tonight, but the only NPN transistors I have are C1740, are they OK? I apologize for my ignorance.

    I'm also interested in sheldons 12v relay being actuated by an opto. I don't know if the camera i-o provides the series resistor mentioned. I'm currently assembling a kit 12v relay that might fit the bill. I realize this low-voltage battery powered remote may not require such an approach, but I have other ideas this digital output might be applied to and so I'm trying to get a very broad understanding of controlling relays and other devices.

    I appreciate all the response on this project - Thank you. I thought this was going to be a simple endeavor when I started many weeks ago - like plugging the i-o leads from the camera directly into the opener and voila! Hah. My skill level is clearly not much more than casual amateur.
     
  11. #12

    Expert

    Nov 30, 2010
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    At first glance, that transistor should work.
     
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