Thursday, May 15, 2008

Syringe Logic Probe

I hope my faithful readers will forgive a quick detour into electronic arts-n-crafts. Rest assured, I won't abandon assembly language to make toilet-paper covers and tea cozies. Instead I intend to demonstrate how a diabetic MacGyver would tap a difficult pin on a circuit board.

After building Sump's Logic Analyzer out of a spare Spartan 3 board, I needed a logic probe with a sharp tip. What's sharp enough to grab a pin on a QFP device or those microscopic columns of solder that are exposed around the perimeter of a QFN device? An insulin syringe, of course!
syringe probe
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.
closeup of syringe tip
I haven't yet tested the probe's electrical properties at high frequencies, but it works well enough for sniffing AES keys from an SPI bus.

--Travis Goodspeed
<travis at>


partridge said...

If you can find a nerve stimulator needle (used for regional nerve blocks) you can pretty much skip the soldering as they come with a lead already attached. As a bonus, they are insulated so only the very tip of the needle is conductive.

Liveer said...

Nice this tip about Syringe

Scott Livingston said...

Howdy. This is quite old, but did you ever investigate high frequency performance? Or various other subtleties in the analog signal domain?

Your hypodermic needle idea still remains quite neighborly for digital, moderate speed probing, and I've used it several times in my work. Cheers.

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