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Newbie Question

Discussion in 'Electronic Basics' started by zero, Nov 11, 2004.

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  1. zero

    zero Guest

    I am a complete newbie in electronics and am about to start some 5V digital
    CMOS and TTL IC projects. Do I have to worry about any safety issues, such
    as resistors catching on fire or electrolytic capacitors exploding if the
    wrong voltage polarity is applied? Anything else that could go wrong that I
    should be concerned about? Thank you.
     
  2. John Larkin

    John Larkin Guest


    With a small wall-wart type power supply, or any supply that
    current-limits below an amp or so, there's no danger... maybe a tiny
    puff of smoke if you toast a resistor or something. No DC voltage
    below 48 will do more than tickle slightly.

    Anything connected to the AC line should be properly constructed
    (UL/CE marked) and grounded if designed for such.

    Go for it!

    John
     
  3. Resistors are not generally much of a worry. Capacitors, however,
    can be dangerous along the lines you mentioned. Tantalum caps are
    notorious for going bang if they've been wired up backwards, or if you
    exceed their voltage rating.

    The way to avoid problems is to watch what the frell you're doing!
    ;-) It is inevitable that you're going to make mistakes. ALL techs do,
    even guys like me who have been at it for 20+ years.

    The right way to approach it is to do the best you can not to
    goof, of course, but also to LEARN from your mistakes and know that, at
    some point, some of those impromptu lessons are going to be expensive
    ones. That's just the risks one faces in the world of electronics.

    Happy tinkering. The world can always use more tinkerers. Have you
    considered getting your amateur radio license?

    Keep the peace(es).


    --
    Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
    (Known to some as Bruce Lane, ARS KC7GR,
    kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
    "If Salvador Dali had owned a computer, would it have been equipped
    with surreal ports?"
     
  4. Use some kind of glasses when working with any kind of engineering,
    protective glasses or magnifying glasses, for example.
    Cheap reading glasses, strength +0.5 or +1.0, are very useful when
    working with electronics.

    When working with high or unknown voltages, keep one hand in your pocket
    and wear insulating shoes.

    Electricity can only hurt you seriously if current finds a path through
    you body. If you only use one hand you do not give the current a chance
    to go through your body. Don't lean with your other hand against the
    kitchen sink while measuring mains voltages :)

    Remember that current makes the muscles cramp, so you cannot simply let
    go of a tool or a wire.

    My father who was an electrician told me about when he was caught in a
    serious situation once. He had climbed 7 meters high on a pole and was
    trying to cut an insulated wire. The wire should have been disconnected
    but it wasn't, so when he got through the insulation he got current
    through his body because his climbing gear touched some grounding wire.

    He could not let go of the wire cutter because his muscles cramped, and
    he felt his mind was going black. He knew that the only way out was
    to cut through the wire completely.

    He slowly woke up again, found himself hugging the pole with both arms to
    avoid falling backwards, breaking both his legs and falling. He had
    managed to cut through the wire before passing out completely.

    As long as you use only low voltages, under 50 Volt, you don't have to
    worry about such problems, but it doesn't hurt to be aware of them.
     
  5. john jardine

    john jardine Guest

    Nothing to worry about. Just be wary of 'lytics (more esp' Tant's), they can
    go with a helluva bang.
    Guy I know buggered the lens in one eye when a reverse connected 47u was
    powered up with 5V. At the time he was a bit short sighted and peering a
    couple of inch above the PCB. (now short of sight :)
     
  6. peterken

    peterken Guest

    - for protection against reverse polarity ALWAYS put a diode anti-parallel
    with the power-supply on the board (it NORMALLY never conducts this way,
    only if supply is reversed)
    - for current limitation use a limited power supply
    - elco's (especially tantalium) might go off with a bang if too high ripple
    frequency passes through them
    - ic's themselves might explode, had 2 or 3 in 24 years or so, so NEVER go
    peeking a circuit too close if testing



    message

    With a small wall-wart type power supply, or any supply that
    current-limits below an amp or so, there's no danger... maybe a tiny
    puff of smoke if you toast a resistor or something. No DC voltage
    below 48 will do more than tickle slightly.

    Anything connected to the AC line should be properly constructed
    (UL/CE marked) and grounded if designed for such.

    Go for it!

    John
     
  7. Steve Evans

    Steve Evans Guest

    The lowest recorded fatlaity with DC was at only 12V! personally, I've
    never felet anything tingling below about 75V. There\s a guy in Poland
    who checks for mains voltage by sticking his fingers into light
    sockets and feeling for a buzz! EVerybody's differnet! Be safe...nver
    underestimate the danger of electricy!
     
  8. John G

    John G Guest

    A series diode would be much better.
    The first time you get it wrong with your parallel diode it could easily
    be destroyed or destroy the wall wart.
    The second time you have no protection.

    Also bottom posting it the accepted good manners here.
     
  9. peterken

    peterken Guest


    series diode won't do the trick if only 5V is available, circuit only gets
    4V3 then....
    and choice of the parallel diode is always done for a type that never
    interrupts, but always shorts if destroyed

    (srry for not bottom posting)
     
  10. Active8

    Active8 Guest

    Funny you'd mention 48 - the typical on hook voltage that bit the
    hell out of the inside of my bicep one sweaty day (I usually have to
    wet my fingertips to feel 90 VAC)
     
  11. peterken

    peterken Guest

    mike

    In Europe the level of "dangerous" is set to 48V
    I assume the "biting 48V" you mention did most damage during a short circuit
    at high current, thus the flash "biting" a piece out of your body parts due
    to burning and not just "touching" it...
    I cannot imagine otherwise, since indeed 48V does nothing more as giving an
    unpleasant feeling
     
  12. John Larkin

    John Larkin Guest

    Nearly all warts are current-limited and protected against shorts.

    And the diode will make the 5v into 4.3.

    John
     
  13. John G

    John G Guest

    The OP never said he had a REGULATED 5volt wall wart, to lose .7 volts
    from, did he?
     
  14. Active8

    Active8 Guest

    On Sat, 13 Nov 2004 11:44:57 GMT, peterken wrote:

    Get youself good and sweaty and let those little solid copper wires
    with the sharp points from the dikes stab you on the fleshy inside
    of the bicep and tell me it doesn't bite. WTF is "unpleasant
    feeling", anyway? Is that a quantifiable amount? Is more than that
    any *less* unpleasant?

    "Bite" - slang for various stuff. "Hot sauce with a bite." "The
    phone line bit me."
     
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