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555 timer IC toys for children with disabilities

Discussion in 'Electronic Basics' started by mark3, Nov 9, 2005.

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  1. mark3

    mark3 Guest

    Hi, can any one help?
    I,m just teaching myself basic electronics and have
    built a hobby kit (9V) using a 555 timer to tigger a LED off/on over
    various lengths of time. Have run a lead from pin 3 of 555 timer IC
    to base of transistor (548) to trigger 9v electric motor without
    success,I have also tried using a 9v relay but again not enough power
    to drive electric motor. My aim is to set up various tigger switchers
    with timming cicuits to drive different toys and lights to help
    stimulate learning for a child with intellectual dissabilities. If any
    one could offer some advise and/or some easy to read circuit diagram's
    in this area it would be greatly appreciated.


    Thankyou

    Mark3
     
  2. Jason

    Jason Guest

    Instead of using a 548 NPN device, perhaps you should try using a
    MOSFET. Bipolar transistors act as a "switch" for current input and
    the maximum output current of the 555 timer (~1mA) will limit the
    current that your 548 can draw from your battery. If you switch this
    to a (high-power?) FET, you will be able to set your own limits within
    your range by picking the right device. FETs work off of the voltage
    levels applied to the gate and you don't have to worry about current
    limitations of the 555 timer.

    This, of course, is all assuming that you've hooked up everything
    correctly and it is a problem with the 548 transister's capabilities.

    gl,

    Jay
     
  3. PeteG

    PeteG Guest

    A 555 timer can source/sink ~200mA so not only could it drive a small relay
    directly it has no problem driving BC548 or a power darlington transistor.
    You should check the manufacturers data sheet for the actual 555 timer you
    are using. The CMOS versions of this chip have lower output ratings.

    Here's a couple of links to show you the way, and if you Google for 555
    timer circuits you'll find a shed load of info'

    http://www.cpemma.co.uk/555pwm.html
    http://www1.jaycar.com.au/images_uploaded/relaydrv.pdf

    Pete
     
  4. What do you mean with not enough power??

    Is the battery going down, or is the driving system not ok?
     
  5. Bob Monsen

    Bob Monsen Guest

    If you have an extra NPN transistor, try this:

    View circuit using 'courier' or other fixed space font:


    9V -------------o---- MOTOR + terminal
    |
    -
    ^
    |
    .---o---- MOTOR - terminal
    | |
    |/ |
    PIN3-[1k]--| |
    |> |
    | |
    | |/
    '-|
    |>
    |
    |
    GND--------------'

    This is called a 'darlington' configuration, and it boosts the output
    with a wimpy input.

    Also, use a 1uF and a 0.01uF cap across the Vcc and Vdd inputs of the
    555, or the voltage drop when the battery turns on may retrigger the
    timer. Even better, use a separate battery, and connect the grounds.

    The diode protects your transistors.

    ---
    Regards,
    Bob Monsen

    Mathematics is nothing more, nothing less, than the exact part of our
    thinking.
    - Luitzen Brouwer
     
  6. mark3

    mark3 Guest

    Hi jay
    Thankyou for your time and help

    Kind regards
    Mark
     
  7. mark3

    mark3 Guest

    Hi jay
    Thankyou for your time and help

    Kind regards
    Mark
     
  8. mark3

    mark3 Guest

    Hi Pete
    Thankyou for your time and help. The web sites are very useful !

    Kind regards
    Mark
     
  9. mark3

    mark3 Guest

    Hi Pete
    Thankyou for your time and help. The web sites are very useful !

    Kind regards
    Mark
     
  10. mark3

    mark3 Guest

    Hi Bob
    Thankyou for your time and help

    Kind regards
    Mark
     
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