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    Test probes with super fine tip

    These test probes wereld made several years ago and have proven to be very useful in many applications. The small tip allows you to probe even the tiniest SMT components.  Because the tip is really, really sharp (don’t ask me how I know… ouch) it allows you to breach residue of solder flux or even penetrate the outer isolation of a cable.

    Best thing, they are very cheap and easy to make yourself:

    • Two fineliners (Hema: this or this ) a €0.80 = €1.60
    • Two 4 mm banana test leads (I would recommend about 1 m) a €7.95 = €15.90
    • Two needles from your wife’s sewing box : free
    • Two Heat shrink tubing 8 mm Ø, 20 mm as a strain relief €1.00
    • Some bits and pieces that you have likely lying around (solder, super glue, two component epoxy, etc)
    • Optional 10 mm heat shrink tubing in the desired color.
    • So grand total is about €20

    If you check the picture below, you’ll see that the few step necessary to make these probes are mostly self explanatory.

    <image>

    Remove the plastic stop at the back (the part that you are normally chewing on) of the fineliner and use some needle nosed pliers or a pincet to extract the cotton ink reservoir. Be careful with the ink, it can really create a mess! From the other side remove the small compressed felt tip. At one end of the cable, snip of the banana plug and measure the diameter of the cable. Drill a hole through the plastic stop, slightly larger than the cable diameter. Slide the narrow heat shrink tubing over the cable, so you can’t forget it later (don’t ask me…) and put the cable through the stop. Strip the cable over a length of ~5 mm. Insert the rear end of the needle in the cable, so it is nicely centered and apply solder to create a solid joint.
    Now insert the assembly through the fineliner’s body all the way to the other end. Insert the needle in the tip until it protrudes about 5 mm . Use a smal amount of two component epoxy to fix the assembly. Now, you’re almost done!
    Put the hole tip and cable assembly back into the fineliner’s body, as well as the back stop. To create your strain relief, apply a small amount of super glue on the stop as well as on the cable near the stop. Shove the heat shrink tubing back, so it covers the cap and use a heat gun or lighter to shrink the tubing.

    Optionally you can now add the large colored heat shrink tubing over your SMT probes. I liked this for it covers the logo of the original manufacturer of the fineliner and the texture of the tubing gives a better grip on the probe than the original flat surface. If you want you can keep the metal clip on the cap, so you can hang your probes from a rail. Since the cap fits quit tight to the body, I decided to remove the clip and cover the part with some tubing as well.

     

    That’s all there is to it. If you assemble all you’re parts and tools up front (something that is always nice to do anyway) you can easily be finishes in an hour and end up with some really nice and useful test probes.

    Have fun making your own!

     

    Cor

    PS 1 – I noticed there are some (cheap) super glue brands that cure so fast they are useless for this application. In order not to ruin you’re almost finished probe, do a quick test.

    PS 2 When making the first set of probes years ago, I found that there are two types of needles: those made of steel and those made of aluminium. The latter being impossible to solder because of the thin layer of aluminium oxide at the outer layer of the needle. If you’re not sure with which variety you’re dealing with, use a magnet to check it out.

     

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