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Oscilloscope Probe Adapter for 0.025" Square Header Pins

This page discusses a simple extension adapter to connect an oscilloscope probe or voltmeter test lead to a standard 0.025" square male header pin. I acquired several commercial versions along with some Tektronix scope probes, but I thought it would be a useful quick project to document how to make one.

The commercial device is a "SAFTLEED" as shown below. The black projection is a receptacle for a standard 0.025" square header pin. The white object is an insulated wire connector that serves as a insulating shell to protect the wire loop. The purpose of this gadget is to provide a safe connection for an oscilloscope ground clip to a standard header pin. Most oscilloscope ground leads have an alligator clip that's too large to easily connect to a header pin without risking shorting adjacent pins.

To use the adapter, you slide the receptacle over the header pin and clip the probe's alligator ground clip onto the wire loop inside the shell. It works well, and can also be used for signal connections, as it's often more convenient than trying to clip the scope probe tip onto a header pin. I have one in red, one green and one dark blue, which makes distinguishing connections easier.
Original "SAFTLEED" as supplied with Tektronix probe set.
 
Parts required:
  • A short length of insulated wire, #22 or #24 AWG (use different colors to distinguish different connections)
  • Short length of heat shrink tubing, preferably color matched to the wire
  • A 0.025" crimp receptacle, Molex P/N 16-02-1125, Mouser P/N  538-16-02-1125.
  • A "closed end wire termination" available at your local hardware store.
 
Install the connector on one end of the wire. Ideally, you will have the correct crimp tool to crimp the connector to the wire. My crimp tool is one size too large, so I soldered the wire to the connector after a loose crimp.
 
Slip the heat shrink tubing over the connector, shrinking it in place.

Drill a hole in the closed wire termination, just large enough for the wire to slide through. I used #24 AWG wire and found a 1/16" drill was a good fit.

Slip the wire termination over the wire as shown.
 
Strip the wire back about 3/4," tin it and form into a loop as shown.

Solder the loop together.
 
Slide the wire termination over the loop. The photo is a bit tricky, but the loop is centered in the opening, so that an alligator clip will grab it. When the alligator clip is  removed, the wire termination shell should shield the loop from inadvertent contact.

You have two options to retain the wire in the termination shell:

  • Crimp the shell
  • Use a small amount of 5-minute epoxy, sufficient to fill the small end of the shell, but not enough to encroach on the wire loop.

I used 5-minute epoxy, but the commercial version is crimped.
 
The completed adapter.
 
Ground lead from a Tektronix probe clipped onto the ring.

Note that the ground lead and ring are protected from accidental contact with other circuit elements.
 
Adapter in use with the Softrock 6.2 lite receiver.

The center pin of the audio output 3-position header is ground. The overall ground length is long for accurate waveform detail when looking at the 40 MHz oscillator, so keep that in mind when interpreting waveforms.