Wireless LED indicator for soldering iron.

Discussion in 'The Projects Forum' started by magnet18, Jan 15, 2011.

  1. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Hi all, I recently had the idea to somehow put a status light on my soldering iron to tell me if its on or off so i don't have to get up and walk across the room to check.
    I don't really have any experience in this area and I was wondering how the best way to go about doing this would be, I was intending to wrap some kind of coil around the power wire to power a little led, I'd be fine with one volt.
    If anyone has any ideas or knows anywhere I can look to find information on this it'd be much appreciated.
    Thanks :)
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Use a neon lamp on the iron's wire. There are inline switches available that have the lamp built in as well.

    LEDs directly off mains current are a sub-optimal solution, neon bulbs come in nearly every color now, and need no additional circuitry.
     
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  3. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Thats probably a better idea, I think I'll do that.
    But, since i still wanna learn about this, what would be the best way to go about doing it, hypothetically speaking?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    What kind of iron do you have?
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Wrapping wire around the cord wouldn't work, as the current in one wire cancels out the current in the other wire (sums to zero). To get any inductive coupling, separate the two wires, and wrap a few turns around one of the wires. Then a small voltage will be produced in that wire relative to the amount of current drawn. This is how "clamp" ammeters function.

    To get enough power to light an LED, you would need to coil both a single wire from the soldering iron cord and the "sense" wire around a core, creating a transformer of sorts. The number of turns would need to be rather high to get enough voltage and current due to non-ideal inductive coupling (core helps this). This current will also be AC (solution doesn't work if power is DC). Because it is AC, the sensed/induced power would need to be rectified and current limited to run the LED.

    There are more complex solutions, but not many simpler solutions.
     
  6. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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  7. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    What if a capacitor was included?
    Could greater output be gained if it was set to... resonate(?) at 60Hz?
    Also, if you have any suggestions for sites about this topic id love to know about them.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Anything in the line cord is just an accident waiting to happen. Possibilities run to a switched outlet in a box with a pilot indicator, or a stand that will sense heat and turn on a lamp.

    If you do any serious work, a soldering station is a better way to go - especially with temperature control at the tip. I'm using a 35 year old Weller WTCP station that has only needed one change of heater.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The problem is frequency. 50/60Hz is a low frequency, so for AC coupling to a low impedance (LED), very, very large values of inductance (transformers) or capacitors are needed.

    There really isn't a way to couple the AC to an LED with a capacitor, which is why "wall warts" weight so much, they are a big chunk of laminated metal wound with copper (transformers). Newer "wall warts" (any that weigh under 1/2 lb roughly), are the switch mode power supply type. Efficiency is a bit higher, weight is reduced, and current sourcing ability is higher.

    SMPS is an entire specialized area of electronics that has advanced quickly. They use small inductors and switches (MOSFETs) to regulate the supply.

    If the power lines ran at 120kHz, then your idea would be a bit simpler, the RFID/anti-shoplifting tags run in that frequency range, and enough power can be induced into the tag's coil to run a tiny transmitter. When you buy an item, they wave the tag over a very powerful 120kHz source which induces so much current in the inductor that it burns out, so it cannot respond to the door sensors.

    I digress... Using a separate power supply, such as 4 AA batteries, you could make a sensitive 60Hz inductive current sensor, which would, in turn light up an LED (Using power from the batteries). There are a few circuits on the net for this, mostly involving a precision rectifier (op-amp) which switches a transistor on or off, dependent on current flow.
     
  10. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    hey, i like that heat idea...
    what would be a good way to do that?

    Also, i would love a soldering station...
    but they cost money...
    any idea where i could get one cheap?
     
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