Soldering In The Dark — Add Some Light To Your Iron!


While [William] may not know what he’s doing (his words, not ours!), at least he can SEE what he’s doing now with this awesome soldering iron light modification. And judging by the build quality, we’d reckon he really does know what he’s doing!

He’s taken a piece of copper-clad PCB, and formed it to create a nice circular copper donut. This allows him to make a ring of LEDs in parallel that will slide nicely over the soldering iron and integrate into the plastic case.

To power it, he’s made a small diode bridge to rectify the AC, and a 24 ohm high-wattage resistor run in series with the heating element. The voltage drop across the resistor is 7.5V max, which equates to about 5.3V RMS minus the diode voltage drops. This means the LEDs see about 4.5V at a total of 135mA, which works out to about 17mA each — just under the approved rating. All of this fits nicely into the original casing of the soldering iron.

Finally to finish it off, he’s MacGyver’d an old pill bottle into a protective casing around the LED ring — it looks surprisingly stock on the soldering iron!

Do you have a tool hack that adds handy features? Let us know through the Tips Line!

33 thoughts on “Soldering In The Dark — Add Some Light To Your Iron!

  1. Aaaarrggh! There’s just *so* much wrong with that simple circuit I hardly know where to begin. I thought LEDs in parallel were bad enough. Then there’s that “unknown wattage” resistor – if it decides that it’s had enough then it’s mains voltage across that exposed PCB. Is the metal tip of the iron earthed? I hope so – yet that that could cause more problems with the push-fit PCB that’s almost in contact with it.

    Well, you can’t say it’s not a hack!

    1. FTFA: “While I was at it, I tapered the edges of the hole so the copper surfaces wouldn’t touch the iron shaft and short.”

      Or you could even go so far as to read the linked writeup where you’d learn that he’s already disconnected “that stuff” for v2.

      While I’m here I’ll point out to the HaD author the text “I drilled it in the middle to fit the shaft of the soldering iron, plus a bit so it’s a loose fit. I then used a file to make the square into a disk.” No hole saw mentioned. While not a large deal, you’re making up build details. Is that part of the new legalese?

      This place is turning into slashdot…

    2. Last I heard, the size of the resistor indicates its wattage rating. Aside from that, looking at the schematic, the LEDs would help to rectify the AC so two of those diodes are not need. Also, he didn’t place any protection for ripples that would normally occur when rectification. If he did, he would have reduce the amount of power being sapped from the iron.

      1. I dunno if a soldering iron minds a choppy supply, it’ll all even out thermally, there’s a lot of heat-inertia, or whatever it’s called, in a soldering iron.

        If this thing runs off the mains, 110VAC, then I’m rather worried he’s using just a resistor to drop the voltage.

  2. I recently searched for a solution to this kind of problem too. Adding more light to whatever I was soldering made it much easier. I was tired of propping up my phone next to my projects with the back LED on.

    I just bought a $5 head mounted LED torch though.

    1. Neither. I’ve soldered in some stupid situations and with stupid tools (lighter and a screwdriver), but never ever in the dark. I can’t imagine a situation where you have power for an iron but not for basic lighting. I didn’t, but really an electric light wouldn’t have helped me-I didn’t have power-that’s the whole point of that particular situation.

    2. In the model railroading field, soldering under a layout is an occasional necessity, but the owners are usually prepared with something like a shop light or head torch. I can actually see where a tight spot could use a lighted soldering iron because a shop light or head-mounted light might just be too far back. However, I would rather power LEDs with a battery pack mounted to the iron. Big irons have lights, but I’ve never seen a pencil iron (and those a bit bigger) with lights.

    3. Well I can’t speak for other people, but sometimes if I have a bit of tricky work to do, I will dim the room and then turn on a point source and point that at just what I am working on.

      I find it removes distractions, and lets me focus on just the bit I need to do. However it would also be invaluable when you need to solder things in situ and not on a well lit bench.

    4. I don’t think the point is to solder in, like, a cave or something; it’s for when your lighting isn’t ideal, like a dorm room with a crappy light fixture and no extra space for lamps, or something like that..

  3. It also needs a shield to block light from the LED’s from coming directly back to his eyes, and reflect it all forward. It is a little over kill, there could have been much fewer LED’s. He could have used very small surface mount type that would be really small and bright. I would say that four would have been more than enough to light any board very well. They would draw less power too.

    1. The power used by the soldering iron dwarfs any power used by the leds.

      “He could have used very small surface mount type that would be really small and bright.”

      They call this site “hackaday” because people use the stuff they have lying around.

      1. Funnily enough, I could not perform this hack with just the stuff I have lying around. I have a temperature-controlled soldering iron, so the LEDs would be off half the time. Also, the heater in it is just 8 ohms, and I don’t have any resistors that small. On the other hand, I do have a lot of leds and some good wire for making a co-axial auxiliary wiring between the iron and the station.

        1. For temperature controlled irons, they tend to use something around 24V
          for the heating element. So it would make more sense to have all the LED
          in series (~ 8 x 3.3V = 26.4V) and connect that to the heater with a
          series resistor. Not that anyone would want to work under a disco strobe
          light as the iron pulses the heater to regulate its temperature.

          I would not do that to my temperature controlled soldering irons. My
          advice is work in a well lit room. Your projects and you would have less
          chance of an accident.

  4. I don’t solder in the dark either, but my aging eyes and continually decreasing part sizes make additional light a necessity. Though, I just use a desk lamp or two nearby to supply the additional light.

  5. Something i really want to see though, DMM probes with light. I often find myself trying to hit that hard to see spot with the probe, and if i shine a strong light at the device it just reflects everywhere. If the light was near the tip it would light only the area around that damned 0402 resistor i need to measure and not the entire wire harness in the way.

    1. I regularly use a measuring and test device called a power probe, its for automotive techs so has a lit probe end for when your upside down in the foot well of a car looking into the abyss of wiring behind the dash! Very handy!

  6. Sorry to bring another negative voice here, but am I right in thinking that each half-phase the + side of the PCB is connected to the full mains voltage (through a diode)? That seems… bad and dangerous.

  7. The problem with the LEDs in parallel is that the one with the lowest voltage treshold will draw most of the current and burn up. Then the next, then the next.

    It’s not a slow process. It’s a cascade failure that is over in seconds once it starts due to the large number of LEDs that are supposed to share the current, which means you’re running the one LED that starts to conduct first at many times the rated current. If they’re sufficiently similiar, it may hold for hours, or if not it may blow up in a few seconds and then they all go pop pop pop.

    1. That depends entirely on the type of LED.

      There is usually no problem running cheap white LEDs in parallel, the high internal resistance takes care of that. I have seen countless LED torches that run a handful of white LEDs in parallel and i have never seen any of them break the LEDs.

      Yes it is bad practice, but it won’t break within hours as you imply.

  8. 50% of the time i feel i need this.
    contrast for me is as important as overall light

    i would personally go for an electricaly isolated solution.
    i mean it involves water for the sponge…
    and water for a sponge usually means a spilled cup…

    although the parallel LEDs are usually “not preferable”,
    I THINK:
    the heat of the iron would lower the voltage of each LED farther then the LED’s individual variation. thus they would all be at the same voltage.
    ie 20c vs 30c is huge difference in voltage. but 300c vs 310c is small differeence and therefore small difference of voltage.
    PLUS what Sven said: …”internal resistance takes care”…

    20c with more then 8 LEDs it matters a lot more

    PS: Sn63/Pb37 rosincore for life!

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