Friday, January 6, 2012

Triggering a DMM with No Hands

Making a DMM measurement on a really really small pin on a chip is not an easy task. You drink a little less coffee that morning and carefully position your probe tip on the pin. Then your frozen scared to move your head to look at the DMM's display in fear the probe tip will slip off before you catch a glimpse of the reading. Has this ever happen to you? In this post we will look at easy way that a colleague of mine came up with to capture a DMM reading on the display without moving your head or your hands.

All you need is a DMM with external triggering capability, a mechanical switch, and some cabling. Here is the setup:

  • Set the DMM for manual external triggering. This means the DMM will only take a measurement on an external trigger event.
  • Position the switch on the ground under your bench by your feet.
  • Wire up the switch to the external trigger input of the DMM
From there position your probe tip on the tiny measurement pin and without taking your eyes off the measurement or moving your hands, toggle the switch with your foot. Remove your probes from the measurement point and look up to view your captured measurement on the DMM display.

When you close the switch with your foot the external triggering input of the DMM is pulled low, which in turn triggers a measurement on the DMM. To avoid the hassle of ordering a switch you could always cannibalize it from an old piece of electronics. For instance, my colleague used an old mouse. They wired a BNC adapter to a switch connected to one of the mouse buttons. The below figures show the mouse setup.

If you have any helpful comments or personal incites to add to this post just use the "Post a Comment" section below.


  1. That was helpfull for some beginners. DMM formation not that simple as amused, but I tried for once. I have been learning for Asic Chip Design. My learning included fast, low power with high speed designs for automotive and electronic desin

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