need help driving 3v 130mA relay coil with 3.3v 20mA

Discussion in 'The Projects Forum' started by ryanmc, Feb 12, 2015.

  1. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    Im working on a project with an ioio board and I need to control a relay coil that spec says is 3v 130mA
    the ioio pin is supposedly 3v 20mA. Im very new to circuit design any suggestions appreciated.
    Ryan
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    You will need a transistor to drive the relay. What is your 3V supply; battery (what type?) or wall-wart?
    Here's how you could do it:-
    RelaySwitching.gif
     
    Last edited: Feb 12, 2015
  3. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    the ioio board puts 3.3v 20ma out on a pin when high and I need to power the 3v 130mA relay with it, the ioio board itself is powered by usb 5v.
    this is going to be in an automobile application.
     
    Last edited: Feb 12, 2015
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Well in my circuit above, just replace the 3V source with 5V and add a 15 Ohm 1W resistor in series with the relay coil.
    I do not recommend this for automobile use; that would be contrary to the Terms of Service of this site.
     
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  5. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    I missed that part about automobile modification in tos I cant seem to edit my post to remove that sentence im not actually modifying automobile per se but sorry for that sentence just the same. And thank you for the awesome tip.
     
  6. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    3 more questions im looking at radio shack they have the following which is better for my need ?
    220 OHM 1/4W 5% CARBON FILM RESISTOR or 1/8 WATT 220 OHM CARBON FILM RESISTORS

    also would the 15 Ohm 1W resistor go in circuit befor or after diode
    and last question is i need to put about 5 of these circuits on a board would that be an issue using the same supply and ground for them all or should i do something differently? i have some spare 7805 regulators from radio shack could I use them to supply the 5v directly from the 12v supply ?
     
  7. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also look at the fet designed for that application in mind, the 2n7000.
    Does not impose any load on the source.
    Max.
     
  9. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    so replace 2n3391a with 2N7000?
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That would be my choice, as long as the load does not exceed 280ma, if greater then there are other higher power logic level FET's to look at.
    Max.
     
  11. Reloadron

    Active Member

    Jan 15, 2015
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    Don't know as this will matter or not but where you mention:

    I saw mention of the 5 volts being from a USB port. You may want to give this a read. While over the years the USB port has evolved and can deliver more current than years ago, it is not a source of unlimited current, even today. So for example if I have 5 relay coils driven by the USB port and each coil draws 130mA then 5 * .130 Amp = 0.650 Amp if all coils are energized at the same time. Just something to keep in mind.

    I would also consider the 2N7000 series which Max has me sold on.

    Ron
     
  12. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    I was thinking about that, the board itself is currently powered from usb but i was thinking about using the 7805's and getting off the usb or leaving the board on the usb but using the 7805's for the relay/coil circuits. maybe 1 7805 for the circuit and 1 for the board? I really appreciate the info and help
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I'd just get a 5V regulated power supply (not 12V) and use 5V relays via the same transistor driver above
    No need for 3V relays.. its just more parts/wasted heat.
     
  14. Reloadron

    Active Member

    Jan 15, 2015
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    That is what I would do, unless of course you are already sitting on a pile of relays with 3 volt coils. :)

    Ron
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That was my assumption when suggesting a resistor in series with the relay coil (and I see no relays in the post #7 shopping list). 5V relays would be better if a 7805 is used; or even use 12V relays and ditch the 7805.
     
  16. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Looking at the specs of the IOIO it seems to accept up to 10V on the Vin pin so thats why I said 5V..
    But he could always just use the 12V supply for the relay side and still power the IOIO by the USB cable.
    Oh so many choices :)
     
  17. ryanmc

    Thread Starter New Member

    Feb 12, 2015
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    When I originally ordered my relays I ordered 12v coils accidentally so I kept them and reordered 3v and the other parts to make circuit. How would I use the 12v relays ?
    I have an ioio that the micro usb came clean off the board and another that the voltage regulator sizzled on I realize there not very expensive but anyone interested in doing the rework and keep one or something? my iron is to big for it and I dont have hot air I was looking at some cheap ones at fleabay but not sure about them.
    Ryan
     
  18. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    What shows as Arduino should be your IOIO..
    +12 from battery is just whatever power supply you have for the relay.. Could be 5V or 12V or 24V or whatever.. You just tie the grounds from the IOIO and the power supply together.

    [​IMG]
     
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