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Simple circuit help

Discussion in 'Electronic Basics' started by dave s, Oct 14, 2003.

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  1. dave s

    dave s Guest

    I essentially know next to nothing in the electronics field so could
    do with a little help.

    I have a microchip pic processor installed in a simple circuit
    (SIMMSTICK) and need to use it to switch an external power circuit
    on/off. I'm guessing I need to use a relay to do this (assuming I've
    correctly guessed the function of a relay) but have no idea how to how
    to hook this up to the PIC nor which type of relay I should be using.

    The external circuit is 1..14V/1A DC . The control circuit operates at
    5V DC.

    Could anyone point me in the right direction?

  2. happyhobit

    happyhobit Guest

    Hi Dave,

    There is a lot you don't say. Can you program? Is somebody going to do the
    wiring for you? O.K. Whatever.

    A PIC can control a FET and this can control a relay. Or the FET can also
    directly control an external circuit.

    Use an N-Channel FET (maybe an STD12NE06) for common ground, the output will
    need a pull-up. Simple, yes.

  3. dave s

    dave s Guest

    I can program & solder, the problem is that my electronics knowledge
    goes no further than what I was taught in school at 15 (as a minor
    part of a physics class).

    By common ground do you mean common to both the external & control
    circuit? If so I'm not sure this is doable - the external power
    circuit is a battery charger with it's own psu.
  4. happyhobit

    happyhobit Guest

    Dave, if you post me direct, with a valid e-mail address, I'll post you a
    circuit. I can't post a JPG to this group.

  5. Rich Webb

    Rich Webb Guest

    You might get some ideas here:
    or elsewhere around the Circuit Cellar site.
  6. CFoley1064

    CFoley1064 Guest

    I have a microchip pic processor installed in a simple circuit
    Try this (view with fixed font like M$ Notepad)...

    VCC (5VDC)

    | | 5V Coil
    1N4002 - _|_ Relay
    ^ |_/_|-
    | |
    | |
    6.8K |
    ___ |/
    o------|___|---o-------| 2N3904
    PIC Output | |>
    .-. |
    | | |
    6.8K | | |
    '-' |
    | |

    created by Andy´s ASCII-Circuit v1.22.310103 Beta

    Try to get a small relay with a 5V coil that has a coil resistance of greater
    than 50 ohms. Connect your external circuit to the contacts of the relay coil.
    If your external circuit is an inductive load, you may have to put a snubber
    across the load to prevent arcing at the relay contacts from upsetting your
    micro. Try sci.electronics.basics next time.

    Good luck.
  7. CFoley1064

    CFoley1064 Guest

    Try sci.electronics.basics next time.

    Oops. Sorry -- it's getting a little late. Thought this was S.E.D. until .083
    sec. after posting.

    Good luck.
  8. dave s

    dave s Guest

    No problem :), it's late here also. Thanks for the circuit. Just one
    quick question re: the snubber - I'm assuming this is also known as a
    contact suppressor (I did say I know next to nothing about
    electronics), does this go across the load or the relay contacts & is
    there an optimum farad/ohm rating I should be looking for?

  9. CFoley1064

    CFoley1064 Guest

    Just one
    It really depends on the type of load you're switching with the relay. If
    you're turning ON/OFF a DC inductive load, you can put a diode across it just
    like the one across the relay coil in the diagram. Just use a diode rated for
    at least twice the current that normally goes thru the load, and at least twice
    the voltage that's across the relay when it's off. I'm reading either 1 to 14
    VDC, 114VDC, or 1.14VDC at 1A on your first post. Without knowing what you're
    switching it's pretty much guesswork, but you might want to try putting a
    1N5403 across your load (cathode on the positive side, of course). It's a safe

    Good luck.
  10. dave s

    dave s Guest

    Thanks Chris, the relay is to be used as a simple ON/OFF switch & the
    VDC is 1 to 14, sorry for the confusion.

    I couldn't find 1N5403s in my suppliers catalog but did find 1N5401s
    which seem to fit in with your description above.

    Many thanks for the help.
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