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control the electrical appliances using PC

Discussion in 'Electronic Basics' started by ryadav, Dec 11, 2005.

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  1. ryadav

    ryadav Guest


    I used the Circuit Diagram mentioned in the below link to "control the
    electrical appliances using PC". But it does not work. Did any one
    worked recently on this, if yes does it works?

    I used the following components

    1. 6 VDC Relay
    2. C2235 NPN transistor
    3. 1N4007 diode
    4. 4.7 K resisitor
    5. LED

    Only LED glows when parallel port passes +5v. As it is metioned in the
    link relays switches
    when parallel port passes +5v which is not happening in my case. Please
    help me in fixing issue. Relay switch is happening in before parallel
    port passes +5v.
  2. ryadav

    ryadav Guest

    what is the wrong in the circuit? why it does not work?

    | Vcc for Relay



    / -------+--------| |---------|

    P data 4.7K B / c | 1N4002 |_|
    -----------/\/\/\/\---------+-----| NPN _____ | relay |home
    | \ e /_\ |-|
    LED X \ +--------| |---------|

    P Ground | | |


    Relay Ground |

  3. ryadav

    ryadav Guest

    Relay will be always glows since diagram shows relay VCC is passed to
    cathod end of diode and relay ground given to anode end of
    diode. should it be like that?
  4. cbm5

    cbm5 Guest

    The circuit is wrong, use the one from
  5. Pooh Bear

    Pooh Bear Guest

    That circuit is defective.

    The base-emitter junction forward voltage should never exceed about 0.7V.
    That's not enough to light the LED which is therefore spurious. You say the
    LED lights which suggests that you miswired the transistor.

  6. Pooh Bear

    Pooh Bear Guest

    The diode is there to 'catch' the flyback pulse when the relay switches
    off ( inductive parts have stored energy ). It's shown connected

  7. Pooh Bear

    Pooh Bear Guest

    cbm5 is correct.

    The circuit you posted is wrong. The relay should be in series with the
    transistor not in parallel. Use the link he supplied.

  8. Jasen Betts

    Jasen Betts Guest

    it needs extra power for the relay. pin 1 of the joystick socket has 5V
    which might be anough, otherwise use a 6V plugpack.

  9. Jasen Betts

    Jasen Betts Guest

    that circuit in that document is bullshit, try the coffee howto instead

    It gives this circuit which is very conventional.
    you ca probably make it work with the parts you have.

    | __|__
    Relay /^\ Diode 1N4002
    Coil /---\
    | |
    | /
    4.7K B |/ C
    parallel port >-\/\/\/\/---| NPN Transistor: BC547A or 2N2222A
    data pi |\ E
    | \
    parallel port >--------------+
    ground pin |

    I'm submitting a bug report on the Home-Electrical-Control document.

  10. Bob Masta

    Bob Masta Guest

    In addition to what others have posted, note that NT-based
    versions of Windows (NT, XP, 2000) don't allow direct access
    to the ports, so you will probably need a special ring 0 driver like
    GIVEIO for them. That won't be needed for Win9x and earlier.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  11. ryadav

    ryadav Guest

    Thank you all, finally it worked with new circuit provided in the URL

  12. Quite a bit seems to be wrong. The thing that catches my attention is
    that, as drawn, the relay will always be "on," regardless of the state
    of the applied data. You've got "Vcc" and "Relay Ground" hard-wired
    across the relay.
  13. Jasen Betts

    Jasen Betts Guest

    if the power supply for the relay is short-circuit protected and rather wimpy
    and the NPN has enough gain. it could work by the NPN shorting out the
    supply and turning the relay off.

    if not the best you can hope of is for it to fail in an unspectacular way.

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