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#36: 3D-printed PCB workstation using acupuncture needles

This was a surprisingly fun and useful project!

Connecting test probes to PCBs can be difficult when the contact points are very small, or when you need to keep the probes in place while using your hands to run tests or use a computer. Normal test probes for multimeters, oscilloscopes, and other equipment have to be held in place.

This amazing 3D-printed PCB workstation uses acupuncture needles as test probes. The test probes are attached to adjustable arms that can hold them in position on the device under test.

Print the parts and make one for your own lab:

Resources

Parts required

You can print the plastic parts yourself using the files provided on Thingiverse, or you can buy a kit from the designer. I printed the parts over the space of a few days while I was working on other things. The base takes a few hours to print and there are many other parts, so don’t try to rush through it. Collect everything you need and lay it out to make sure you have it all.

  • Probe arms: 3D-printed parts, M4 bolt with hex head, washer, and M4 wing nut
  • Pack of acupuncture needles (I used these ones in 0.35x40mm size)
  • 3D-printed base plate
  • PCB mounts: 3D-printed bracket, M5 bolt with hex head, washer, and M5 wing nut
  • light-weight, flexible hook-up wire
  • Pin headers
  • Heat-shrink tubing (I used 3mm on the pin headers, and 1.5mm on the needles)
  • Self-adhesive rubber feet
  • Ferrules and crimper: useful if acupuncture needs have stainless steel ends

Assemble base and pcb holders

The Thingiverse project includes both large and small PCB holders. I’ve only printed the small ones so far. Thread an M5 bolt up through the base and a bracket, and put an M5 washer and wing-nut on top. Make sure the bracket can slide along the slot.

Stick a rubber foot under each corner of the base, to help it sit securely on your bench and give the bolt heads enough clearance to slide without sticking.

Assemble probe brackets

Insert the vertical bracket into the mounting base. I used a drop of superglue to lock it in place.

Danger! If you put superglue into the mounting base and then squeeze in the vertical bracket, the superglue can squirt out under high pressure. Be very careful that you don’t squirt it into your eyes!

The handles of the acupuncture probes that I bought are about 1.3mm in diameter, and didn’t fit into the mounting clips. I drilled out the clips with a 1.5mm drill, and used super-glue to attach them in place with most of the handle sticking out the top.

The mounting clips are a press-fit into the horizontal arm. Use super-glue to fix them permanently.

Pass an M4 bolt through the vertical mount and horizontal arm, then put an M4 washer and wing-nut on it.

If the end of the acupuncture needle is plain steel, you can solder the wire directly onto it. My acupuncture needles are all stainless steel so I used a ferrule with the plastic cover removed, and crimped the wire onto the end of the needle.

I put 1.5mm heat-shrink tubing over the needle, with just the end exposed. This is optional but it may help prevent the probes from short-circuiting against each other.

Thread the wire along the horizontal arm. What you put on the other end of the wire is up to you: I soldered on a pin header and then put heat-shrink tubing over the joint. Alternatively, you could put on an alligator clip, a banana plug, a spring clip, or whatever suits you.

Usage

With the device under test mounted on the base, press-fit test probes into the base. Use the handles on the test probes to rotate them, and tighten the wing nut when the needle is in position.

The needles are quite springy, so it’s easy to adjust their position with a pair of tweezers after they are approximately right. The heat-shrink on the needle helps with this, because it’s easy to grip with the tweezers.

8 thoughts on “#36: 3D-printed PCB workstation using acupuncture needles

  1. Looks really nice. The leads get pretty long for high-speed signals and hence the noise you showed on the ‘scope trace, but plenty good enough for most tasks.

    1. Yes, for anything that’s noise sensitive it’d be best to use shielded cable. Having 50cm of plain hook-up wire wandering across the bench isn’t great for noise immunity! I think most of the time I’ll just be using this to hook up serial connections, or re-flash a target board, or leave a multimeter connected while I do something to the board.

    2. You could use a shielded cable and use two holder for the cable. Basically run the cable close to the pcb and split it. Attach the shield/ground to one holder and than attach the core wire to the second holder. I also would replace the needle with a 3d printed rod and then attach just the tip of the needle to the end of the rod so you dont have that long antenna.

  2. Thanks for introducing me to the jig, very very handy. I wrote a small post on it which will go live tommorow on Hackaday. https://hackaday.com/blog/

    1. Thanks Danie, that’s amazing! I really appreciate it.

  3. Hi great tutroial, are needles sizes 0.25x25mm ?

    1. I used 0.35 x 40mm. I think 0.25 might be too thin and springy. Thanks for asking this, because I should have specified it in the instructions. I’ll update the page now to add that info.

  4. Hi!
    Will ferrite sleeves on both ends of the wire help against noise? Or is it better to wrap the wire in foil and heat-shrink tube? Ferrite sleeves like this have Ф1.5mm https://i.imgur.com/OMSJrH5.png

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