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1vdc relay circuit

  1. Jan 20, 2010 #1
    Okay, admittedly I am not that well versed in electronics. I can solder and follow directions well enough to put together some interesting hacks occasionally, but I'm really a greenie when it comes to certain aspects.

    I'm trying to find a reasonable way to accomplish turning on and off a device that is powered by about 3.6vdc. The trigger mechanism would be a cell phone's vibration motor's power source (motor disconnected) which outputs somewhere around 1 - 1.3vdc.

    I started this project by using a simple relay circuit controlled by a serial port of a computer, but now want to move it to the cellular angle - which gives me much lower power output unless I go with some sort of bluetooth serial adaptor (which I'm working on as well). For now though, if anybody has ideas on a simple scenario for a quick switching relay circuit that would work for this scenario, I'd really appreciate the assistance.

    Thanks
     
  2. jcsd
  3. Jan 20, 2010 #2

    berkeman

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    Staff: Mentor

    I'm not real comfortble with this question. Thread locked for a bit...
     
  4. Jan 20, 2010 #3

    berkeman

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    Okay, after some side discussion, I'm re-opening the thread.

    1V is really too low to run much of a relay, but plenty to turn on a transistor. Just use an NPN transistor to ground as your switch. Take your output and drive the base through a resistor, ground the emitter, and put the collector to one side of the motor. The other side of the motor goes to your battery + supply.
     
  5. Jan 20, 2010 #4
    Okay, this sounds do-able. I've attached a really cheesy drawing of what I believe that you're describing. Basically confirming that I need to tie the grounds of the two devices together, and treat the output of the collector as the "ground" for my motor being driven, and attach the motor directly to the positive side of the power supply.

    I'd read that if I'm driving a motor from this circuit that I should probably include a diode between the 3.3vdc+ and the output of the collector so that the transistor is protected from any spikes, would you agree with this summation?

    Thanks a BUNCH for your advice :)

    https://www.physicsforums.com/attachment.php?attachmentid=23210&stc=1&d=1264018597
     

    Attached Files:

  6. Jan 20, 2010 #5

    berkeman

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    Well done. And yes, a diode across the motor is a good idea, with the cathode to the + terminal and the anode to the - terminal. Do you know if the phone output signal is DC or pulsed?
     
  7. Jan 20, 2010 #6
    Thank you!

    It appears that power is dc power but it turns on and off quickly when the phone rings in vibrate mode. This is a function of the software from what I can tell. My application will actually be a piece of software running on the phone, so I will be turning the power on and off as needed rather than letting it pulse from the ringer's logic routine. I'll have to test this tonight by running the app and measuring the output when I am directly driving it, to be sure.
     
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