Just don’t stick yourself!
The tip is razer sharp, easily digging far enough into a pin to hold its place. A finger’s weight on the plunger keeps the probe in place; it has never once slipped to short two pins, as my multimeter’s probe is wont to do.
2 thoughts on “Make a logic probe from a syringe”
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I used to work near a guitar shop and used to ask for the cut off bass guitar strings. The ones that had a stainless steel core wound with a larger diameter brass wire worked nicely. I would cut off a useful length, tin both ends (leave the middle unsoldered to retain springiness), use a file/sandpaper/Dremel/grinder/bit of concrete to make one end pointy. Solder the non pointy end to a broken meter probe, or else make your own using epoxy and old Bic pens. Slip a piece of spaghetti tubing over the guitar string and leave the pointy end exposed. The brass is easy to solder to and the stainless steel core gets nice and sharp. Not only have I used these guitar strings as probes, but with a little wiggling (and no heat) they’ll punch through and reopen solder holes. The only problem I’ve had with them is that they do get dull after a while and need to be resharpened and will get shorter with use, so it’s a good idea to make the probes easily replaceable. I’m pretty sure my probes might be a bit more inductive than the syringe would be.